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Change in Description
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- ~~-This page was written by Dr Rob Williams~~
- -
- This references section is not exhaustive but provides key sources of research information that informs and supports the statements and suggestions given.
- Ball, S. L. 1983. Pathogenic variability of downy mildew (Sclerospora graminicola) on pearl millet I. Host cultivar reactions to infection by different pathogen isolates. Annals of Applied Biology 102:257-264.
- Ball. S.L., Pike, D. & Burridge, C. 1986. Characterisations of populations of Sclerospora graminicola. Annals of Applied Biology 108: 519-526.
- Michelmore, R.W., Pawar, M.N. & Williams, R.J. 1982. Heterothallism in Sclerospora graminicola. Phytopathology 72:1368-1372.
- Rachie, K.O. & Majmudar, J.V. 1980. Pearl millet. The Pennsylvania State University Press. 307 pp.
- Sharma, R., Upadhyaya, H.D., Sharma, S., Gate, V.L. & Raj, C. 2015. New Sources of Resistance to Multiple Pathotypes of Sclerospora graminicola in the Pearl Millet Mini Core Germplasm Collection. Crop Science 55:(4) 1619-1628.
- Singh, A.K., Rao, V.P., Rai, K.N., Kulkarni, V.N. & Thakur, R.P. 2004. Effectiveness of Within-progeny Selection for Downy Mildew Resistance in Pearl Millet. International Sorghum and millets newsletter, 45. 
- Singh, S.D. 1995. Downy mildew of pearl millet. Plant Disease 79: 545-550.
- Singh, S.D. & Gopinath, R. 1985. A seedling inoculation technique for detecting downy mildew resistance in pearl millet. Plant Disease 69: 582-584.
- Singh, S.D. & King, S. B. 1988. Recovery resistance to downy mildew in pearl millet. Plant Disease 72: 425-428.
- Singh, S.D. & Williams, R.J. 1980. The role of sporangia in the epidemiology of pearl millet downy mildew. Phytopathology 70: 1187-1190.
- Singh, S.D., King, S.B. & Werder, J. 1983. Downy mildew disease of pearl millet. ICRISAT information Bulletin no. 37, 30 pp.
- Thakur RP, Rao VP, Wu BM, Subbarao KV, Shetty HS, Singh G, Lukose C, Panwar MS, Sereme P, Hess DE, Gupta SC, Datta VV, Panicker S, Pawar NB, Bhangale GT and Panchbhai SD. 2004. Host resistance stability to downy mildew in pearl millet and pathogenic variability in Sclerospora graminicola. Crop Protection 23 (10): 901- 908.
- Thakur, R.P., Shetty, H.S. & Khairwal, I.S. 2006. Pearl Millet Downy Mildew Research in India: Progress and Perspectives. Journal of SAT Agricultural Research 2: (1)
- Weltzien, E. & King, S.B. 1995. Recurrent selection for downy mildew resistance in pearl millet. Plant Breeding 114: 302- 312.
- Werder, J. & Ball, S.L. 1992. Variability of pearl millet downy mildew (Sclerospora graminicola) and its implications for breeding for stable and durable resistance. Tropical Pest Management 38 (1): 43 - 47.
- Williams R. J., Singh, S. D. & Pawar, M.N. 1981. An improved field screening technique for downy mildew resistance in pearl millet. Plant Disease 65, 239 - 241.
- Williams R. J. & Singh, S. D. 1981. Control of pearl millet downy mildew by seed treatment with Metalaxyl. Annals of Applied Biology 97: 263 - 268.
- Williams, R. J. & Andrews, D. J. 1983. Breeding for disease and pest resistance in pearl millet. FAO Plant Protection Bulletin, 31 (4), 136-158.
- Williams, R. J. 1984. Downy Mildews of Tropical Cereals. Advances in Plant Pathology 2: 1-103.
Edited by Rob Williams at June 17, 2019 15 : 05 : 47
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- +++ /tmp/diffy20191112-2177-1fc9ifh 2019-11-12 20:24:27.274037690 +0000
- @@ -1 +0,0 @@
- ~~-Reference~~
- --- /tmp/diffy20191112-2177-1aowb7o 2019-11-12 20:24:27.274037690 +0000
- +++ /tmp/diffy20191112-2177-q3rsq1 2019-11-12 20:24:27.274037690 +0000
- @@ -1,41 +0,0 @@
- ~~-This page was written by Dr Rob Williams~~
- -
- ~~-This references section is not exhaustive but provides key sources of research information that informs and supports the statements and suggestions given.~~
- -
- -Ball, S. L. 1983. Pathogenic variability of downy mildew (Sclerospora graminicola) on pearl millet I. Host cultivar reactions to infection by different pathogen isolates. Annals of Applied Biology 102:257-264.
- -
- -Ball. S.L., Pike, D. & Burridge, C. 1986. Characterisations of populations of Sclerospora graminicola. Annals of Applied Biology 108: 519-526.
- -
- -Michelmore, R.W., Pawar, M.N. & Williams, R.J. 1982. Heterothallism in Sclerospora graminicola. Phytopathology 72:1368-1372.
- -
- ~~-Rachie, K.O. & Majmudar, J.V. 1980. Pearl millet. The Pennsylvania State University Press. 307 pp.~~
- -
- -Sharma, R., Upadhyaya, H.D., Sharma, S., Gate, V.L. & Raj, C. 2015. New Sources of Resistance to Multiple Pathotypes of Sclerospora graminicola in the Pearl Millet Mini Core Germplasm Collection. Crop Science 55:(4) 1619-1628.
- -
- -Singh, A.K., Rao, V.P., Rai, K.N., Kulkarni, V.N. & Thakur, R.P. 2004. Effectiveness of Within-progeny Selection for Downy Mildew Resistance in Pearl Millet. International Sorghum and millets newsletter, 45. 
- -
- ~~-Singh, S.D. 1995. Downy mildew of pearl millet. Plant Disease 79: 545-550.~~
- -
- -Singh, S.D. & Gopinath, R. 1985. A seedling inoculation technique for detecting downy mildew resistance in pearl millet. Plant Disease 69: 582-584.
- -
- ~~-Singh, S.D. & King, S. B. 1988. Recovery resistance to downy mildew in pearl millet. Plant Disease 72: 425-428.~~
- -
- -Singh, S.D. & Williams, R.J. 1980. The role of sporangia in the epidemiology of pearl millet downy mildew. Phytopathology 70: 1187-1190.
- -
- ~~-Singh, S.D., King, S.B. & Werder, J. 1983. Downy mildew disease of pearl millet. ICRISAT information Bulletin no. 37, 30 pp.~~
- -
- -Thakur RP, Rao VP, Wu BM, Subbarao KV, Shetty HS, Singh G, Lukose C, Panwar MS, Sereme P, Hess DE, Gupta SC, Datta VV, Panicker S, Pawar NB, Bhangale GT and Panchbhai SD. 2004. Host resistance stability to downy mildew in pearl millet and pathogenic variability in Sclerospora graminicola. Crop Protection 23 (10): 901- 908.
- -
- -Thakur, R.P., Shetty, H.S. & Khairwal, I.S. 2006. Pearl Millet Downy Mildew Research in India: Progress and Perspectives. Journal of SAT Agricultural Research 2: (1)
- -
- ~~-Weltzien, E. & King, S.B. 1995. Recurrent selection for downy mildew resistance in pearl millet. Plant Breeding 114: 302- 312.~~
- -
- -Werder, J. & Ball, S.L. 1992. Variability of pearl millet downy mildew (Sclerospora graminicola) and its implications for breeding for stable and durable resistance. Tropical Pest Management 38 (1): 43 - 47.
- -
- -Williams R. J., Singh, S. D. & Pawar, M.N. 1981. An improved field screening technique for downy mildew resistance in pearl millet. Plant Disease 65, 239 - 241.
- -
- -Williams R. J. & Singh, S. D. 1981. Control of pearl millet downy mildew by seed treatment with Metalaxyl. Annals of Applied Biology 97: 263 - 268.
- -
- -Williams, R. J. & Andrews, D. J. 1983. Breeding for disease and pest resistance in pearl millet. FAO Plant Protection Bulletin, 31 (4), 136-158.
- -
- ~~-Williams, R. J. 1984. Downy Mildews of Tropical Cereals. Advances in Plant Pathology 2: 1-103.~~
Edited by Rob Williams at June 17, 2019 15 : 05 : 07
- --- /tmp/diffy20191112-2177-erlgpg 2019-11-12 20:24:27.282037750 +0000
- +++ /tmp/diffy20191112-2177-451w4a 2019-11-12 20:24:27.282037750 +0000
- @@ -1 +0,0 @@
- ~~-Management Options~~
- --- /tmp/diffy20191112-2177-ujogmh 2019-11-12 20:24:27.286037780 +0000
- +++ /tmp/diffy20191112-2177-1mwzf2j 2019-11-12 20:24:27.286037780 +0000
- @@ -1,188 +0,0 @@
- ~~-1. Use of Resistant Cultivars~~
- -
- ~~-1.1 What is host-plant resistance and does it exist for pearl millet downy mildew?~~
- -
- -Host-plant resistance is the ability of a plant to resist becoming diseased when challenged by a pathogen which is able to cause disease in other plants in that species.
- -
- ~~-Host-plant resistance can have various mechanisms which are conferred by genes within the plant.~~
- -
- -Host-plant resistance does exist within pearl millet against the downy mildew pathogen and has been harnessed through plant breeding to develop downy mildew resistant cultivars.
- -
- ~~-1.2 How is host-plant resistance to pearl millet downy mildew detected and used?~~
- -
- -Host-plant resistance for pearl millet downy mildew is detected by exposing pearl millet plants to inoculum of the pathogen under environmental conditions conducive for infection.
- -
- -Initial attempts to screen for resistance were made using "sick-plots" in which diseased plant tissue containing oospores had been incorporated into the soil. This method had several drawbacks, including: a) the uncertainity of the quantity and evenness of distribution of the inoculum in the soil; b) the time taken to establish an effective "sick-plot"; and c) lack of flexibility in the size and location of the screening area.
- -
- -Once the role of sporangia in the epidemiology of the disease had been recognised, large-scale screening for resistance was possible in which the size and location of the screening area was highly flexible and the inoculum challenge was uniform throughout the screening area. The large-scale screening method for downy mildew resistance developed by the pearl millet improvement team at ICRISAT in India is shown in photographs Fig 27- 28.
- -
- -"Infector rows" of a highly susceptible variety are sown first throughout the screening area leaving room for later sowing of eight rows of plants to be screened between every pair of infector rows. The disease is promoted in the infector rows using pots of pre-infected plants placed at regular intervals along the infector rows with overhead sprinkler irrigation used to create the necessary humidity for sporulation and disease spread. When the disease is developing uniformly in the infector rows, and 50-60% of the plants have symptoms, the test rows are sown, together with an occasional row of a highly susceptible cultivar to act as a check on the effectiveness and uniformity of the challenge to the test rows. This screening technique enabled the screening for resistance of thousands of germplasm lines and breeding materials of pearl millet so that resistance could be identified and incorporated into advanced breeding lines to develop downy mildew resistant cultivars with high yield and high-quality grain.
- -
- ~~-<table>~~
- ~~- <tbody>~~
- ~~- <tr>~~
- ~~- <td>~~
- - <img alt="" longdesc="Rob Williams" src="//s3.amazonaws.com/plantvillage-production/var/www/sites/production.plantvillage.org/releases/20171216094632/public/ckeditor_assets/pictures/90/content_Screen_Shot_2018-01-11_at_2.28.20_PM.jpg" style="width: 200px; height: 150px; border-top-left-radius: 10px; border-top-right-radius: 10px; border-bottom-right-radius: 10px; border-bottom-left-radius: 10px;" title="PMDM 27: Large-Scale field screening for PMDM resistance, showing how the infector rows are exposed to inoculum of diseased potted plants produced specifically for this purpose, and sprinkler irrigation used to provide the needed humidity" /><img alt="" src="https://s3.amazonaws.com/plantvillage-production-new/ckeditor_assets/pictures/155/content_PV_PMDM_Fig_27.jpg" style="width: 300px; height: 206px;" />
- -
- - Fig 27: Large scale field screening                       
- ~~- </td>~~
- ~~- <td>~~
- - <img alt="" src="https://s3.amazonaws.com/plantvillage-production-new/ckeditor_assets/pictures/156/content_PV_PMDM_Fig_28.jpg" style="width: 300px; height: 201px;" /><img alt="" longdesc="Rob Williams" src="//s3.amazonaws.com/plantvillage-production/var/www/sites/production.plantvillage.org/releases/20171216094632/public/ckeditor_assets/pictures/91/content_Screen_Shot_2018-01-11_at_2.28.44_PM.jpg" style="width: 200px; height: 150px; border-top-left-radius: 10px; border-top-right-radius: 10px; border-bottom-right-radius: 10px; border-bottom-left-radius: 10px;" title="PMDM 28: Large-scale field screening system for PMDM resistance, showing infector rows after every 8 test rows" />
- -
- - Fig 28: Infector rows after every 8 test rows                  
- ~~- </td>~~
- ~~- <td>~~
- - <img alt="" src="https://s3.amazonaws.com/plantvillage-production-new/ckeditor_assets/pictures/159/content_PV_PMDMFig_29.jpg" style="width: 300px; height: 450px;" /><img alt="" longdesc="Rob Williams" src="//s3.amazonaws.com/plantvillage-production/var/www/sites/production.plantvillage.org/releases/20171216094632/public/ckeditor_assets/pictures/92/content_Screen_Shot_2018-01-11_at_2.28.53_PM.jpg" style="width: 200px; height: 150px; border-top-left-radius: 10px; border-top-right-radius: 10px; border-bottom-right-radius: 10px; border-bottom-left-radius: 10px;" title="PMDM 29: Screening for resistance to downy mildew in pearl millet in a large scale field screening nursery; note the highly diseased infector row (right), a highly susceptible test row (center) and a highly resistant test row (left). Also note the white parchment bags on the panicles of the resistant plants enable crossing to be done between and among resistant plants." />
- -
- ~~- Fig 29: Showing infector row, highly susceptible and resistant test row  ~~
- ~~- </td>~~
- ~~- </tr>~~
- ~~- <tr>~~
- ~~- <td>~~
- - <img alt="" src="https://s3.amazonaws.com/plantvillage-production-new/ckeditor_assets/pictures/160/content_PV_PMDM_Fig_30.jpg" style="width: 300px; height: 451px;" /><img alt="" longdesc="Rob Williams" src="//s3.amazonaws.com/plantvillage-production/var/www/sites/production.plantvillage.org/releases/20171216094632/public/ckeditor_assets/pictures/93/content_Screen_Shot_2018-01-11_at_2.29.01_PM.jpg" style="width: 200px; height: 150px; border-top-left-radius: 10px; border-top-right-radius: 10px; border-bottom-right-radius: 10px; border-bottom-left-radius: 10px;" title="PMDM 30: A few downy mildew resistant plants have been found in a pearl millet germplasm line that is otherwise highly susceptible to the disease. The white parchment bags on the panicles of the resistant plants indicate that the plant breeding process is underway to produce a downy mildew resistant version of this pearl millet accession." />
- -
- ~~- Fig 30: White parchment bags on the panicles of the resistant plants~~
- ~~- </td>~~
- ~~- <td>~~
- - <img alt="" src="https://s3.amazonaws.com/plantvillage-production-new/ckeditor_assets/pictures/172/content_PV_PMDM_Fig_31.jpg" style="width: 300px; height: 205px;" /><img alt="" longdesc="Rob Williams" src="//s3.amazonaws.com/plantvillage-production/var/www/sites/production.plantvillage.org/releases/20171216094632/public/ckeditor_assets/pictures/94/content_Screen_Shot_2018-01-11_at_2.29.14_PM.jpg" style="width: 200px; height: 150px; border-top-left-radius: 10px; border-top-right-radius: 10px; border-bottom-right-radius: 10px; border-bottom-left-radius: 10px;" title="PMDM 31: Shows the result of selection within a highly PMDM susceptible line can produce a highly resistant version of that line." />
- -
- ~~- Fig 31: Selection within a highly PMDM susceptible line ~~
- ~~- </td>~~
- ~~- <td> </td>~~
- ~~- </tr>~~
- ~~- </tbody>~~
- ~~-</table>~~
- -
- ~~-1.3 Can downy mildew resistance be identified in the laboratory or greenhouse?~~
- -
- -A glasshouse screening technique has been developed in which potted seedlings are inoculated at the coleoptile stage with a suspension of sporangia and kept in high humidity at about 25 C for infection and disease development. The technique is precise, independent of the season, and both time-efficient and cost-effective. The technique has been used to screen breeding lines for resistance to downy mildew and to study pathogenic variability within the pearl millet pathotype.
- -
- ~~-1.4 What progress has been made in finding and using host-plant resistance to pearl millet downy mildew?~~
- -
- -In the ICRISAT Pearl Millet Improvement Programme more than 3,100 pearl millet germplasm accessions from about 25 countries were screened for resistance to downy mildew in the period from 1977 to 1992, and 428 accessions were detected with high levels of downy mildew resistance combined with a flowering time of 45 to 60 days.
- -
- -Selected sources of downy mildew resistant pearl millet lines were combined at ICRISAT to produce open-pollinated varieties that were released for cultivation in India. One of these, WC-C75 has been cultivated by Indian farmers since 1983 in nine Indian states covering a total of more than 1 million hectares.
- -
- -Selection within downy mildew susceptible accessions and breeding lines that possess desirable traits such as high grain quality, drought tolerance, short stature etc. has enable the development of new downy-mildew resistant versions of those accessions/lines that have then been used to produce valuable downy mildew resistant cultivars and hybrids (see Fig 31)
- -
- -In India, the national All India Coordinated Millet Improvement Programme of the Indian Council of Agricultural Research has identified many sources of resistance to downy mildew in pearl millet and used the resistance to develop high-yielding downy mildew resistant hybrids and cultivars. These have been multiplied and distributed to farmers through the national seed production system and also by indigenous private sector seed companies.
- -
- -In West Africa, ICRISAT in collaboration with the Institute National d'Etude et de Recherche Agricole (INERA) in Burkina Faso has developed several promising downy mildew resistant pearl millet varieties such as the IKMP series.
- -
- ~~-1.5 Have sources of resistance been identified that are effective at locations throughout India and West Africa?~~
- -
- -The International Pearl Millet Downy Mildew Nursery (IPMDMN), coordinated by ICRISAT in cooperation with scientists in national research programmes enabled the screening of pearl millet lines for stability of resistance at many locations in West Africa and India over several years. More than 50 pearl millet lines were identified with stable downy mildew resistance across locations and years. Many of these lines originated from northern Nigeria.
- -
- -In West Africa a regional downy mildew screening programme, the West African Downy Mildew Nursery, testing pearl lines contributed by national research scientists at disease "hot spots", identified pearl millet lines with resistance that was effective across the region.
- -
- ~~-1.6 Is there evidence of resistance "breakdown" by new pathogenic races when resistant cultivars are widely grown?~~
- -
- -In India, some downy mildew resistant F1 hybrids, which are genetically uniform, have become susceptible to the disease after their widespread use, as the pathogen has responded to the selection pressure of the resistance.
- -
- -In contrast, the genetically diverse open-pollinated pearl millet cultivars such as WC-C75 have retained their downy-mildew resistance when grown widely for several years over large areas. It is assumed that the genetic heterogeneity of open-pollinated varieties provides a buffering against virulence shifts by the downy mildew pathogen. These varieties will not remain totally disease free, but neither is it likely that damaging epidemics of downy mildew will develop.
- -
- ~~-1.7 What strategies are recommended for the use of downy mildew resistant pearl millet F1 hybrids, to avoid resistance breakdown?~~
- -
- ~~-The deployment of a single F1 hybrid for several years over a large area is likely to lead to the breakdown of the resistance.~~
- -
- ~~-Recommendations to avoid resistance breakdown of the F1 hybrids include:~~
- -
- ~~-i. grow several genetically different hybrids at the same time within a region;~~
- -
- ~~-ii. deploy different hybrids sequentially over time.~~
- -
- -For these strategies to be effective several desirable hybrids with different resistance genotypes must be available and there would need to be a co-ordinated system of seed production and distribution servicing an informed community of farmers.
- -
- ~~-1.8 What is "recovery resistance" to downy mildew in pearl millet?~~
- -
- -Research at ICRISAT has identified pearl millet lines in which infected young plants appear to outgrow the pathogen and produce normal grain-bearing heads. This phenomenon has been termed recovery resistance. Selection within pearl millet lines demonstrating some plants with apparent recovery resistance has produced lines with up to 95% of the plants which although infected and showing symptoms of the disease at the vegetative stage go on to develop normal grain-bearing panicles. The value of this recovery resistance is not clear though it has been theorised that the use of such recovery resistance in F1 hybrids may enable the prolonged use of the hybrids with a to reduce risk of resistance breakdown.
- -
- ~~-1.9 From where are resistant varieties available?~~
- -
- -High-yielding downy mildew resistant cultivars of pearl millet have been developed by ICRISAT (http://explorer.icrisat.org/page/pearl_millet/680/275) and several national agricultural research organisations, as well as by private-sector seed companies. Growers wanting access to these cultivars need to contact the national agricultural research and extension services in their country for advice on availability and use strategies.
- -
- ~~- ~~
- -
- ~~-2. Fungicide Seed Treatment~~
- -
- ~~-2.1 Can fungicide seed treatment control pearl millet downy mildew?~~
- -
- ~~-Complete control of pearl millet downy mildew can be achieved even in highly susceptible cultivars by seed treatment with appropriate fungicides (Fig 32).~~
- -
- ~~-2.2 Which fungicides are effective as seed treatments for controlling pearl millet downy mildew?~~
- -
- -High levels of control of pearl millet downy mildew have been achieved by seed treatment with fungicides containing the active ingredients metalaxyl (e.g Apron SD 35) and mefenoxam (e.g Apron XL).
- -
- -The active ingredients metalaxyl and mefenoxam move systemically within plants grown from treated seed which makes them ideal for the control of the systemic pearl millet downy mildew.
- -
- -Apron 35 SD has been highly effective when applied at the rate of 2 g active ingredient per kg seed. The treatment process is simple and only small quantities of the fungicide are needed.
- -
- -The fungicides based on metalaxyl and mefenoxam are patented and registered for use by Syngenta Crop Protection from where further information on the products, where they are registered for use, their environmental impact etc. can be obtained.
- -
- -Effective control of pearl millet downy mildew has also been reported on an experimental basis by seed treatment with a formulation (Melody® Duo) of the fungicide active ingredient Iprovalicarb. However, it is registered and recommended for use only as a foliar spray in potato and grape crops. There are reports of downy mildew control with foliar sprays of systemic fungicides, particularly those containing metalaxyl as the active ingredient. However, the use of foliar sprays has no advantage over seed treatment in terms of level of control achievable, and has several disadvantages in that it requires the farmer to have spraying equipment and the means to make up the spray at the correct concentration, it exposes the farmers and the environment to spray drift and contamination, and it is likely to be more expensive.
- -
- ~~-<table>~~
- ~~- <tbody>~~
- ~~- <tr>~~
- ~~- <td>~~
- - <img alt="" src="https://s3.amazonaws.com/plantvillage-production-new/ckeditor_assets/pictures/162/content_PV_PMDM_Fig_32.jpg" style="width: 300px; height: 201px;" /><img alt="" longdesc="Rob Williams" src="//s3.amazonaws.com/plantvillage-production/var/www/sites/production.plantvillage.org/releases/20180123061925/public/ckeditor_assets/pictures/96/content_Picture1-min.png" style="width: 200px; height: 150px; border-top-left-radius: 10px; border-top-right-radius: 10px; border-bottom-right-radius: 10px; border-bottom-left-radius: 10px;" title="PMDM 32: The complete control of downy mildew in the highly susceptible pearl millet hybrid NHB3 by seed treatment with a metalaxyl containing fungicide (left) with two severely diseased rows growing from untreated seed alongside (right). " />
- -
- ~~- Fig 32: Difference between treated and untreated seeds~~
- ~~- </td>~~
- ~~- </tr>~~
- ~~- </tbody>~~
- ~~-</table>~~
- -
- ~~-3. On-farm Actions for Integrated Pathogen Management (IPM)~~
- -
- ~~-3.1 What do farmers need to take effective on-farm actions?~~
- -
- -Knowledge is the Key. If farmers have information on the nature of the factors adversely affecting their crop, how these factors damage the crop and what is known on how to reduce the damaging effects, then the farmers will be able to find ways that work for them, using the resources available to them within their operating environment. This leads to locally-effective and achievable Integrated Pathogen Management (IPM).
- -
- ~~-3.2 What actions can farmers take to reduce the problem of pearl millet downy mildew?~~
- -
- ~~-The key on-farm actions that farmers can take are sanitation and selection.~~
- -
- ~~-a) remove downy mildew diseased plants from the crop as soon as they are detected;~~
- -
- ~~-b) ensure grain is not threshed with diseased plant parts;~~
- -
- ~~-c) ensure seed for next year's crop is selected from robust disease-free plants.~~
- -
- ~~-3.3 What are the benefits of removing downy mildew diseased plants?~~
- -
- -a) reduce secondary spread: The Secondary spread of downy mildew within a crop is caused by the spores produced on the leaves of diseased plants, so removal of diseased plants or tillers at the first sign of disease will reduce secondary spread within the crop;
- -
- -b) reduce oospore reservoir in soil: As oospores form in diseased plant parts and get into the soil from diseased crop residues, removal of diseased plants from fields at the earliest opportunity not only reduces the secondary spread within the crop but also reduces the oospore "bank" or reservoir in the soil, which will reduce the incidence of primary infection in subsequent seasons;
- -
- -c) prevent oospore contamination of seed: when grain is threshed in the presence of diseased leaves and panicles, oospores are released to contaminate the grain, so removal of diseased plants reduces oospore contamination of seed;
- -
- -d) delay the build-up of new pathogenic races: the selection pressure imposed by the use of highly downy-mildew resistant cultivars can result in the emergence and spread of new pathogenic races of the pathogen capable of overcoming the resistance, so removal of diseased plants at the earliest opportunity will delay the build-up of the new pathogenic race(s) within the local pathogen population;
- -
- -e) delay the build-up of resistance to fungicides: downy-mildew plant pathogens are capable of responding to the selection pressure of the use of highly effective fungicides by developing pathotypes that are able to resist the fungicide, so removal of diseased plants in a crop grown from fungicide-treated seed will delay the build-up of new fungicide-resistant pathogenic race(s) within the local pathogen population;
- -
- -f) reduce downy mildew susceptibility levels in local cultivars: pearl millet is highly cross-pollinated, so pollen from diseased plants can be dispersed widely within the crop to fertilise non-diseased plants; removal of diseased plants prior to flowering (emergence of the grain-bearing heads) prevents the pollen from those plants perpetuating and spreading susceptibility within the gene-pool of the local cultivars;
- -
- ~~-3.4 How can farmers increase levels host-plant resistance to pearl millet downy mildew in their local cultivars?~~
- -
- ~~-Farmers can increase the levels of downy mildew resistance in their local cultivars by:~~
- -
- -i. removing downy mildew diseased plants before the plants flower, so that they do not receive pollen to produce seed and do not produce pollen to fertilize other plants:
- -
- ~~-ii. collecting seed to be used for sowing next year's crop from disease-free plants~~
- -
- -These actions should reduce the level of susceptibility in the local cultivars gene pool, and lead to the development of a population of locally downy-mildew resistant cultivars.
- -
- ~~-3.5 Why is community action beneficial for the control of pearl millet downy mildew?~~
- -
- -Integrated pathogen management will be more effective if done on a community basis rather than by individual farmers acting alone, as sporangia causing secondary spread and pollen from diseased plants can be carried to neighbors' fields.
- -
- -The basis for effective on-farm actions is for all the farmers in the community to fully understand the biology and epidemiology of pearl millet downy mildew and work together to reduce the levels of the disease.
- -
- ~~-3.6 Summary of Options for Integrated Management of Pearl Millet Downy mildew~~
- -
- ~~-• Grow cultivars that are resistant to the pathogen~~
- -
- ~~-• Use appropriate systemic fungicide seed-treatments~~
- -
- -• Practise on-farm sanitation to: a) reduce secondary spread; b) reduce oospore reservoir in soil; c) prevent oospore contamination of seed; d) delay build-up of pathotypes that can break down resistance and resist fungicides; e) build up resistance levels in local cultivars. 
Edited by Rob Williams at June 17, 2019 15 : 05 : 07
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- +++ /tmp/diffy20191112-2177-kclowu 2019-11-12 20:24:27.294037840 +0000
- @@ -1 +0,0 @@
- ~~-Reference~~
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- @@ -1,41 +0,0 @@
- ~~-This page was written by Dr Rob Williams~~
- -
- ~~-This references section is not exhaustive but provides key sources of research information that informs and supports the statements and suggestions given.~~
- -
- -Ball, S. L. 1983. Pathogenic variability of downy mildew (Sclerospora graminicola) on pearl millet I. Host cultivar reactions to infection by different pathogen isolates. Annals of Applied Biology 102:257-264.
- -
- -Ball. S.L., Pike, D. & Burridge, C. 1986. Characterisations of populations of Sclerospora graminicola. Annals of Applied Biology 108: 519-526.
- -
- -Michelmore, R.W., Pawar, M.N. & Williams, R.J. 1982. Heterothallism in Sclerospora graminicola. Phytopathology 72:1368-1372.
- -
- ~~-Rachie, K.O. & Majmudar, J.V. 1980. Pearl millet. The Pennsylvania State University Press. 307 pp.~~
- -
- -Sharma, R., Upadhyaya, H.D., Sharma, S., Gate, V.L. & Raj, C. 2015. New Sources of Resistance to Multiple Pathotypes of Sclerospora graminicola in the Pearl Millet Mini Core Germplasm Collection. Crop Science 55:(4) 1619-1628.
- -
- -Singh, A.K., Rao, V.P., Rai, K.N., Kulkarni, V.N. & Thakur, R.P. 2004. Effectiveness of Within-progeny Selection for Downy Mildew Resistance in Pearl Millet. International Sorghum and millets newsletter, 45. 
- -
- ~~-Singh, S.D. 1995. Downy mildew of pearl millet. Plant Disease 79: 545-550.~~
- -
- -Singh, S.D. & Gopinath, R. 1985. A seedling inoculation technique for detecting downy mildew resistance in pearl millet. Plant Disease 69: 582-584.
- -
- ~~-Singh, S.D. & King, S. B. 1988. Recovery resistance to downy mildew in pearl millet. Plant Disease 72: 425-428.~~
- -
- -Singh, S.D. & Williams, R.J. 1980. The role of sporangia in the epidemiology of pearl millet downy mildew. Phytopathology 70: 1187-1190.
- -
- ~~-Singh, S.D., King, S.B. & Werder, J. 1983. Downy mildew disease of pearl millet. ICRISAT information Bulletin no. 37, 30 pp.~~
- -
- -Thakur RP, Rao VP, Wu BM, Subbarao KV, Shetty HS, Singh G, Lukose C, Panwar MS, Sereme P, Hess DE, Gupta SC, Datta VV, Panicker S, Pawar NB, Bhangale GT and Panchbhai SD. 2004. Host resistance stability to downy mildew in pearl millet and pathogenic variability in Sclerospora graminicola. Crop Protection 23 (10): 901- 908.
- -
- -Thakur, R.P., Shetty, H.S. & Khairwal, I.S. 2006. Pearl Millet Downy Mildew Research in India: Progress and Perspectives. Journal of SAT Agricultural Research 2: (1)
- -
- ~~-Weltzien, E. & King, S.B. 1995. Recurrent selection for downy mildew resistance in pearl millet. Plant Breeding 114: 302- 312.~~
- -
- -Werder, J. & Ball, S.L. 1992. Variability of pearl millet downy mildew (Sclerospora graminicola) and its implications for breeding for stable and durable resistance. Tropical Pest Management 38 (1): 43 - 47.
- -
- -Williams R. J., Singh, S. D. & Pawar, M.N. 1981. An improved field screening technique for downy mildew resistance in pearl millet. Plant Disease 65, 239 - 241.
- -
- -Williams R. J. & Singh, S. D. 1981. Control of pearl millet downy mildew by seed treatment with Metalaxyl. Annals of Applied Biology 97: 263 - 268.
- -
- -Williams, R. J. & Andrews, D. J. 1983. Breeding for disease and pest resistance in pearl millet. FAO Plant Protection Bulletin, 31 (4), 136-158.
- -
- ~~-Williams, R. J. 1984. Downy Mildews of Tropical Cereals. Advances in Plant Pathology 2: 1-103.~~
Edited by Rob Williams at June 17, 2019 15 : 04 : 16
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- @@ -1 +0,0 @@
- ~~-Management Options~~
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- @@ -1,188 +0,0 @@
- ~~-1. Use of Resistant Cultivars~~
- -
- ~~-1.1 What is host-plant resistance and does it exist for pearl millet downy mildew?~~
- -
- -Host-plant resistance is the ability of a plant to resist becoming diseased when challenged by a pathogen which is able to cause disease in other plants in that species.
- -
- ~~-Host-plant resistance can have various mechanisms which are conferred by genes within the plant.~~
- -
- -Host-plant resistance does exist within pearl millet against the downy mildew pathogen and has been harnessed through plant breeding to develop downy mildew resistant cultivars.
- -
- ~~-1.2 How is host-plant resistance to pearl millet downy mildew detected and used?~~
- -
- -Host-plant resistance for pearl millet downy mildew is detected by exposing pearl millet plants to inoculum of the pathogen under environmental conditions conducive for infection.
- -
- -Initial attempts to screen for resistance were made using "sick-plots" in which diseased plant tissue containing oospores had been incorporated into the soil. This method had several drawbacks, including: a) the uncertainity of the quantity and evenness of distribution of the inoculum in the soil; b) the time taken to establish an effective "sick-plot"; and c) lack of flexibility in the size and location of the screening area.
- -
- -Once the role of sporangia in the epidemiology of the disease had been recognised, large-scale screening for resistance was possible in which the size and location of the screening area was highly flexible and the inoculum challenge was uniform throughout the screening area. The large-scale screening method for downy mildew resistance developed by the pearl millet improvement team at ICRISAT in India is shown in photographs Fig 27- 28.
- -
- -"Infector rows" of a highly susceptible variety are sown first throughout the screening area leaving room for later sowing of eight rows of plants to be screened between every pair of infector rows. The disease is promoted in the infector rows using pots of pre-infected plants placed at regular intervals along the infector rows with overhead sprinkler irrigation used to create the necessary humidity for sporulation and disease spread. When the disease is developing uniformly in the infector rows, and 50-60% of the plants have symptoms, the test rows are sown, together with an occasional row of a highly susceptible cultivar to act as a check on the effectiveness and uniformity of the challenge to the test rows. This screening technique enabled the screening for resistance of thousands of germplasm lines and breeding materials of pearl millet so that resistance could be identified and incorporated into advanced breeding lines to develop downy mildew resistant cultivars with high yield and high-quality grain.
- -
- ~~-<table>~~
- ~~- <tbody>~~
- ~~- <tr>~~
- ~~- <td>~~
- - <img alt="" longdesc="Rob Williams" src="//s3.amazonaws.com/plantvillage-production/var/www/sites/production.plantvillage.org/releases/20171216094632/public/ckeditor_assets/pictures/90/content_Screen_Shot_2018-01-11_at_2.28.20_PM.jpg" style="width: 200px; height: 150px; border-top-left-radius: 10px; border-top-right-radius: 10px; border-bottom-right-radius: 10px; border-bottom-left-radius: 10px;" title="PMDM 27: Large-Scale field screening for PMDM resistance, showing how the infector rows are exposed to inoculum of diseased potted plants produced specifically for this purpose, and sprinkler irrigation used to provide the needed humidity" /><img alt="" src="https://s3.amazonaws.com/plantvillage-production-new/ckeditor_assets/pictures/155/content_PV_PMDM_Fig_27.jpg" style="width: 300px; height: 206px;" />
- -
- - Fig 27: Large scale field screening                       
- ~~- </td>~~
- ~~- <td>~~
- - <img alt="" src="https://s3.amazonaws.com/plantvillage-production-new/ckeditor_assets/pictures/156/content_PV_PMDM_Fig_28.jpg" style="width: 300px; height: 201px;" /><img alt="" longdesc="Rob Williams" src="//s3.amazonaws.com/plantvillage-production/var/www/sites/production.plantvillage.org/releases/20171216094632/public/ckeditor_assets/pictures/91/content_Screen_Shot_2018-01-11_at_2.28.44_PM.jpg" style="width: 200px; height: 150px; border-top-left-radius: 10px; border-top-right-radius: 10px; border-bottom-right-radius: 10px; border-bottom-left-radius: 10px;" title="PMDM 28: Large-scale field screening system for PMDM resistance, showing infector rows after every 8 test rows" />
- -
- - Fig 28: Infector rows after every 8 test rows                  
- ~~- </td>~~
- ~~- <td>~~
- - <img alt="" src="https://s3.amazonaws.com/plantvillage-production-new/ckeditor_assets/pictures/159/content_PV_PMDMFig_29.jpg" style="width: 300px; height: 450px;" /><img alt="" longdesc="Rob Williams" src="//s3.amazonaws.com/plantvillage-production/var/www/sites/production.plantvillage.org/releases/20171216094632/public/ckeditor_assets/pictures/92/content_Screen_Shot_2018-01-11_at_2.28.53_PM.jpg" style="width: 200px; height: 150px; border-top-left-radius: 10px; border-top-right-radius: 10px; border-bottom-right-radius: 10px; border-bottom-left-radius: 10px;" title="PMDM 29: Screening for resistance to downy mildew in pearl millet in a large scale field screening nursery; note the highly diseased infector row (right), a highly susceptible test row (center) and a highly resistant test row (left). Also note the white parchment bags on the panicles of the resistant plants enable crossing to be done between and among resistant plants." />
- -
- ~~- Fig 29: Showing infector row, highly susceptible and resistant test row  ~~
- ~~- </td>~~
- ~~- </tr>~~
- ~~- <tr>~~
- ~~- <td>~~
- - <img alt="" src="https://s3.amazonaws.com/plantvillage-production-new/ckeditor_assets/pictures/160/content_PV_PMDM_Fig_30.jpg" style="width: 300px; height: 451px;" /><img alt="" longdesc="Rob Williams" src="//s3.amazonaws.com/plantvillage-production/var/www/sites/production.plantvillage.org/releases/20171216094632/public/ckeditor_assets/pictures/93/content_Screen_Shot_2018-01-11_at_2.29.01_PM.jpg" style="width: 200px; height: 150px; border-top-left-radius: 10px; border-top-right-radius: 10px; border-bottom-right-radius: 10px; border-bottom-left-radius: 10px;" title="PMDM 30: A few downy mildew resistant plants have been found in a pearl millet germplasm line that is otherwise highly susceptible to the disease. The white parchment bags on the panicles of the resistant plants indicate that the plant breeding process is underway to produce a downy mildew resistant version of this pearl millet accession." />
- -
- ~~- Fig 30: White parchment bags on the panicles of the resistant plants~~
- ~~- </td>~~
- ~~- <td>~~
- - <img alt="" src="https://s3.amazonaws.com/plantvillage-production-new/ckeditor_assets/pictures/172/content_PV_PMDM_Fig_31.jpg" style="width: 300px; height: 205px;" /><img alt="" longdesc="Rob Williams" src="//s3.amazonaws.com/plantvillage-production/var/www/sites/production.plantvillage.org/releases/20171216094632/public/ckeditor_assets/pictures/94/content_Screen_Shot_2018-01-11_at_2.29.14_PM.jpg" style="width: 200px; height: 150px; border-top-left-radius: 10px; border-top-right-radius: 10px; border-bottom-right-radius: 10px; border-bottom-left-radius: 10px;" title="PMDM 31: Shows the result of selection within a highly PMDM susceptible line can produce a highly resistant version of that line." />
- -
- ~~- Fig 31: Selection within a highly PMDM susceptible line ~~
- ~~- </td>~~
- ~~- <td> </td>~~
- ~~- </tr>~~
- ~~- </tbody>~~
- ~~-</table>~~
- -
- ~~-1.3 Can downy mildew resistance be identified in the laboratory or greenhouse?~~
- -
- -A glasshouse screening technique has been developed in which potted seedlings are inoculated at the coleoptile stage with a suspension of sporangia and kept in high humidity at about 25 C for infection and disease development. The technique is precise, independent of the season, and both time-efficient and cost-effective. The technique has been used to screen breeding lines for resistance to downy mildew and to study pathogenic variability within the pearl millet pathotype.
- -
- ~~-1.4 What progress has been made in finding and using host-plant resistance to pearl millet downy mildew?~~
- -
- -In the ICRISAT Pearl Millet Improvement Programme more than 3,100 pearl millet germplasm accessions from about 25 countries were screened for resistance to downy mildew in the period from 1977 to 1992, and 428 accessions were detected with high levels of downy mildew resistance combined with a flowering time of 45 to 60 days.
- -
- -Selected sources of downy mildew resistant pearl millet lines were combined at ICRISAT to produce open-pollinated varieties that were released for cultivation in India. One of these, WC-C75 has been cultivated by Indian farmers since 1983 in nine Indian states covering a total of more than 1 million hectares.
- -
- -Selection within downy mildew susceptible accessions and breeding lines that possess desirable traits such as high grain quality, drought tolerance, short stature etc. has enable the development of new downy-mildew resistant versions of those accessions/lines that have then been used to produce valuable downy mildew resistant cultivars and hybrids (see Fig 31)
- -
- -In India, the national All India Coordinated Millet Improvement Programme of the Indian Council of Agricultural Research has identified many sources of resistance to downy mildew in pearl millet and used the resistance to develop high-yielding downy mildew resistant hybrids and cultivars. These have been multiplied and distributed to farmers through the national seed production system and also by indigenous private sector seed companies.
- -
- -In West Africa, ICRISAT in collaboration with the Institute National d'Etude et de Recherche Agricole (INERA) in Burkina Faso has developed several promising downy mildew resistant pearl millet varieties such as the IKMP series.
- -
- ~~-1.5 Have sources of resistance been identified that are effective at locations throughout India and West Africa?~~
- -
- -The International Pearl Millet Downy Mildew Nursery (IPMDMN), coordinated by ICRISAT in cooperation with scientists in national research programmes enabled the screening of pearl millet lines for stability of resistance at many locations in West Africa and India over several years. More than 50 pearl millet lines were identified with stable downy mildew resistance across locations and years. Many of these lines originated from northern Nigeria.
- -
- -In West Africa a regional downy mildew screening programme, the West African Downy Mildew Nursery, testing pearl lines contributed by national research scientists at disease "hot spots", identified pearl millet lines with resistance that was effective across the region.
- -
- ~~-1.6 Is there evidence of resistance "breakdown" by new pathogenic races when resistant cultivars are widely grown?~~
- -
- -In India, some downy mildew resistant F1 hybrids, which are genetically uniform, have become susceptible to the disease after their widespread use, as the pathogen has responded to the selection pressure of the resistance.
- -
- -In contrast, the genetically diverse open-pollinated pearl millet cultivars such as WC-C75 have retained their downy-mildew resistance when grown widely for several years over large areas. It is assumed that the genetic heterogeneity of open-pollinated varieties provides a buffering against virulence shifts by the downy mildew pathogen. These varieties will not remain totally disease free, but neither is it likely that damaging epidemics of downy mildew will develop.
- -
- ~~-1.7 What strategies are recommended for the use of downy mildew resistant pearl millet F1 hybrids, to avoid resistance breakdown?~~
- -
- ~~-The deployment of a single F1 hybrid for several years over a large area is likely to lead to the breakdown of the resistance.~~
- -
- ~~-Recommendations to avoid resistance breakdown of the F1 hybrids include:~~
- -
- ~~-i. grow several genetically different hybrids at the same time within a region;~~
- -
- ~~-ii. deploy different hybrids sequentially over time.~~
- -
- -For these strategies to be effective several desirable hybrids with different resistance genotypes must be available and there would need to be a co-ordinated system of seed production and distribution servicing an informed community of farmers.
- -
- ~~-1.8 What is "recovery resistance" to downy mildew in pearl millet?~~
- -
- -Research at ICRISAT has identified pearl millet lines in which infected young plants appear to outgrow the pathogen and produce normal grain-bearing heads. This phenomenon has been termed recovery resistance. Selection within pearl millet lines demonstrating some plants with apparent recovery resistance has produced lines with up to 95% of the plants which although infected and showing symptoms of the disease at the vegetative stage go on to develop normal grain-bearing panicles. The value of this recovery resistance is not clear though it has been theorised that the use of such recovery resistance in F1 hybrids may enable the prolonged use of the hybrids with a to reduce risk of resistance breakdown.
- -
- ~~-1.9 From where are resistant varieties available?~~
- -
- -High-yielding downy mildew resistant cultivars of pearl millet have been developed by ICRISAT (http://explorer.icrisat.org/page/pearl_millet/680/275) and several national agricultural research organisations, as well as by private-sector seed companies. Growers wanting access to these cultivars need to contact the national agricultural research and extension services in their country for advice on availability and use strategies.
- -
- ~~- ~~
- -
- ~~-2. Fungicide Seed Treatment~~
- -
- ~~-2.1 Can fungicide seed treatment control pearl millet downy mildew?~~
- -
- ~~-Complete control of pearl millet downy mildew can be achieved even in highly susceptible cultivars by seed treatment with appropriate fungicides (Fig 32).~~
- -
- ~~-2.2 Which fungicides are effective as seed treatments for controlling pearl millet downy mildew?~~
- -
- -High levels of control of pearl millet downy mildew have been achieved by seed treatment with fungicides containing the active ingredients metalaxyl (e.g Apron SD 35) and mefenoxam (e.g Apron XL).
- -
- -The active ingredients metalaxyl and mefenoxam move systemically within plants grown from treated seed which makes them ideal for the control of the systemic pearl millet downy mildew.
- -
- -Apron 35 SD has been highly effective when applied at the rate of 2 g active ingredient per kg seed. The treatment process is simple and only small quantities of the fungicide are needed.
- -
- -The fungicides based on metalaxyl and mefenoxam are patented and registered for use by Syngenta Crop Protection from where further information on the products, where they are registered for use, their environmental impact etc. can be obtained.
- -
- -Effective control of pearl millet downy mildew has also been reported on an experimental basis by seed treatment with a formulation (Melody® Duo) of the fungicide active ingredient Iprovalicarb. However, it is registered and recommended for use only as a foliar spray in potato and grape crops. There are reports of downy mildew control with foliar sprays of systemic fungicides, particularly those containing metalaxyl as the active ingredient. However, the use of foliar sprays has no advantage over seed treatment in terms of level of control achievable, and has several disadvantages in that it requires the farmer to have spraying equipment and the means to make up the spray at the correct concentration, it exposes the farmers and the environment to spray drift and contamination, and it is likely to be more expensive.
- -
- ~~-<table>~~
- ~~- <tbody>~~
- ~~- <tr>~~
- ~~- <td>~~
- - <img alt="" src="https://s3.amazonaws.com/plantvillage-production-new/ckeditor_assets/pictures/162/content_PV_PMDM_Fig_32.jpg" style="width: 300px; height: 201px;" /><img alt="" longdesc="Rob Williams" src="//s3.amazonaws.com/plantvillage-production/var/www/sites/production.plantvillage.org/releases/20180123061925/public/ckeditor_assets/pictures/96/content_Picture1-min.png" style="width: 200px; height: 150px; border-top-left-radius: 10px; border-top-right-radius: 10px; border-bottom-right-radius: 10px; border-bottom-left-radius: 10px;" title="PMDM 32: The complete control of downy mildew in the highly susceptible pearl millet hybrid NHB3 by seed treatment with a metalaxyl containing fungicide (left) with two severely diseased rows growing from untreated seed alongside (right). " />
- -
- ~~- Fig 32: Difference between treated and untreated seeds~~
- ~~- </td>~~
- ~~- </tr>~~
- ~~- </tbody>~~
- ~~-</table>~~
- -
- ~~-3. On-farm Actions for Integrated Pathogen Management (IPM)~~
- -
- ~~-3.1 What do farmers need to take effective on-farm actions?~~
- -
- -Knowledge is the Key. If farmers have information on the nature of the factors adversely affecting their crop, how these factors damage the crop and what is known on how to reduce the damaging effects, then the farmers will be able to find ways that work for them, using the resources available to them within their operating environment. This leads to locally-effective and achievable Integrated Pathogen Management (IPM).
- -
- ~~-3.2 What actions can farmers take to reduce the problem of pearl millet downy mildew?~~
- -
- ~~-The key on-farm actions that farmers can take are sanitation and selection.~~
- -
- ~~-a) remove downy mildew diseased plants from the crop as soon as they are detected;~~
- -
- ~~-b) ensure grain is not threshed with diseased plant parts;~~
- -
- ~~-c) ensure seed for next year's crop is selected from robust disease-free plants.~~
- -
- ~~-3.3 What are the benefits of removing downy mildew diseased plants?~~
- -
- -a) reduce secondary spread: The Secondary spread of downy mildew within a crop is caused by the spores produced on the leaves of diseased plants, so removal of diseased plants or tillers at the first sign of disease will reduce secondary spread within the crop;
- -
- -b) reduce oospore reservoir in soil: As oospores form in diseased plant parts and get into the soil from diseased crop residues, removal of diseased plants from fields at the earliest opportunity not only reduces the secondary spread within the crop but also reduces the oospore "bank" or reservoir in the soil, which will reduce the incidence of primary infection in subsequent seasons;
- -
- -c) prevent oospore contamination of seed: when grain is threshed in the presence of diseased leaves and panicles, oospores are released to contaminate the grain, so removal of diseased plants reduces oospore contamination of seed;
- -
- -d) delay the build-up of new pathogenic races: the selection pressure imposed by the use of highly downy-mildew resistant cultivars can result in the emergence and spread of new pathogenic races of the pathogen capable of overcoming the resistance, so removal of diseased plants at the earliest opportunity will delay the build-up of the new pathogenic race(s) within the local pathogen population;
- -
- -e) delay the build-up of resistance to fungicides: downy-mildew plant pathogens are capable of responding to the selection pressure of the use of highly effective fungicides by developing pathotypes that are able to resist the fungicide, so removal of diseased plants in a crop grown from fungicide-treated seed will delay the build-up of new fungicide-resistant pathogenic race(s) within the local pathogen population;
- -
- -f) reduce downy mildew susceptibility levels in local cultivars: pearl millet is highly cross-pollinated, so pollen from diseased plants can be dispersed widely within the crop to fertilise non-diseased plants; removal of diseased plants prior to flowering (emergence of the grain-bearing heads) prevents the pollen from those plants perpetuating and spreading susceptibility within the gene-pool of the local cultivars;
- -
- ~~-3.4 How can farmers increase levels host-plant resistance to pearl millet downy mildew in their local cultivars?~~
- -
- ~~-Farmers can increase the levels of downy mildew resistance in their local cultivars by:~~
- -
- -i. removing downy mildew diseased plants before the plants flower, so that they do not receive pollen to produce seed and do not produce pollen to fertilize other plants:
- -
- ~~-ii. collecting seed to be used for sowing next year's crop from disease-free plants~~
- -
- -These actions should reduce the level of susceptibility in the local cultivars gene pool, and lead to the development of a population of locally downy-mildew resistant cultivars.
- -
- ~~-3.5 Why is community action beneficial for the control of pearl millet downy mildew?~~
- -
- -Integrated pathogen management will be more effective if done on a community basis rather than by individual farmers acting alone, as sporangia causing secondary spread and pollen from diseased plants can be carried to neighbors' fields.
- -
- -The basis for effective on-farm actions is for all the farmers in the community to fully understand the biology and epidemiology of pearl millet downy mildew and work together to reduce the levels of the disease.
- -
- ~~-3.6 Summary of Options for Integrated Management of Pearl Millet Downy mildew~~
- -
- ~~-• Grow cultivars that are resistant to the pathogen~~
- -
- ~~-• Use appropriate systemic fungicide seed-treatments~~
- -
- -• Practise on-farm sanitation to: a) reduce secondary spread; b) reduce oospore reservoir in soil; c) prevent oospore contamination of seed; d) delay build-up of pathotypes that can break down resistance and resist fungicides; e) build up resistance levels in local cultivars. 
Edited by Rob Williams at June 17, 2019 15 : 04 : 16
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- 1. Use of Resistant Cultivars
- 1.1 What is host-plant resistance and does it exist for pearl millet downy mildew?
- Host-plant resistance is the ability of a plant to resist becoming diseased when challenged by a pathogen which is able to cause disease in other plants in that species.
- Host-plant resistance can have various mechanisms which are conferred by genes within the plant.
- Host-plant resistance does exist within pearl millet against the downy mildew pathogen and has been harnessed through plant breeding to develop downy mildew resistant cultivars.
- 1.2 How is host-plant resistance to pearl millet downy mildew detected and used?
- Host-plant resistance for pearl millet downy mildew is detected by exposing pearl millet plants to inoculum of the pathogen under environmental conditions conducive for infection.
- Initial attempts to screen for resistance were made using "sick-plots" in which diseased plant tissue containing oospores had been incorporated into the soil. This method had several drawbacks, including: a) the uncertainity of the quantity and evenness of distribution of the inoculum in the soil; b) the time taken to establish an effective "sick-plot"; and c) lack of flexibility in the size and location of the screening area.
- Once the role of sporangia in the epidemiology of the disease had been recognised, large-scale screening for resistance was possible in which the size and location of the screening area was highly flexible and the inoculum challenge was uniform throughout the screening area. The large-scale screening method for downy mildew resistance developed by the pearl millet improvement team at ICRISAT in India is shown in photographs Fig 27- 28.
- "Infector rows" of a highly susceptible variety are sown first throughout the screening area leaving room for later sowing of eight rows of plants to be screened between every pair of infector rows. The disease is promoted in the infector rows using pots of pre-infected plants placed at regular intervals along the infector rows with overhead sprinkler irrigation used to create the necessary humidity for sporulation and disease spread. When the disease is developing uniformly in the infector rows, and 50-60% of the plants have symptoms, the test rows are sown, together with an occasional row of a highly susceptible cultivar to act as a check on the effectiveness and uniformity of the challenge to the test rows. This screening technique enabled the screening for resistance of thousands of germplasm lines and breeding materials of pearl millet so that resistance could be identified and incorporated into advanced breeding lines to develop downy mildew resistant cultivars with high yield and high-quality grain.
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- <img alt="" longdesc="Rob Williams" src="//s3.amazonaws.com/plantvillage-production/var/www/sites/production.plantvillage.org/releases/20171216094632/public/ckeditor_assets/pictures/90/content_Screen_Shot_2018-01-11_at_2.28.20_PM.jpg" style="width: 200px; height: 150px; border-top-left-radius: 10px; border-top-right-radius: 10px; border-bottom-right-radius: 10px; border-bottom-left-radius: 10px;" title="PMDM 27: Large-Scale field screening for PMDM resistance, showing how the infector rows are exposed to inoculum of diseased potted plants produced specifically for this purpose, and sprinkler irrigation used to provide the needed humidity" /><img alt="" src="https://s3.amazonaws.com/plantvillage-production-new/ckeditor_assets/pictures/155/content_PV_PMDM_Fig_27.jpg" style="width: 300px; height: 206px;" />
- Fig 27: Large scale field screening                       
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- <img alt="" src="https://s3.amazonaws.com/plantvillage-production-new/ckeditor_assets/pictures/156/content_PV_PMDM_Fig_28.jpg" style="width: 300px; height: 201px;" /><img alt="" longdesc="Rob Williams" src="//s3.amazonaws.com/plantvillage-production/var/www/sites/production.plantvillage.org/releases/20171216094632/public/ckeditor_assets/pictures/91/content_Screen_Shot_2018-01-11_at_2.28.44_PM.jpg" style="width: 200px; height: 150px; border-top-left-radius: 10px; border-top-right-radius: 10px; border-bottom-right-radius: 10px; border-bottom-left-radius: 10px;" title="PMDM 28: Large-scale field screening system for PMDM resistance, showing infector rows after every 8 test rows" />
- Fig 28: Infector rows after every 8 test rows                  
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- <img alt="" src="https://s3.amazonaws.com/plantvillage-production-new/ckeditor_assets/pictures/159/content_PV_PMDMFig_29.jpg" style="width: 300px; height: 450px;" /><img alt="" longdesc="Rob Williams" src="//s3.amazonaws.com/plantvillage-production/var/www/sites/production.plantvillage.org/releases/20171216094632/public/ckeditor_assets/pictures/92/content_Screen_Shot_2018-01-11_at_2.28.53_PM.jpg" style="width: 200px; height: 150px; border-top-left-radius: 10px; border-top-right-radius: 10px; border-bottom-right-radius: 10px; border-bottom-left-radius: 10px;" title="PMDM 29: Screening for resistance to downy mildew in pearl millet in a large scale field screening nursery; note the highly diseased infector row (right), a highly susceptible test row (center) and a highly resistant test row (left). Also note the white parchment bags on the panicles of the resistant plants enable crossing to be done between and among resistant plants." />
- Fig 29: Showing infector row, highly susceptible and resistant test row  
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- <img alt="" src="https://s3.amazonaws.com/plantvillage-production-new/ckeditor_assets/pictures/160/content_PV_PMDM_Fig_30.jpg" style="width: 300px; height: 451px;" /><img alt="" longdesc="Rob Williams" src="//s3.amazonaws.com/plantvillage-production/var/www/sites/production.plantvillage.org/releases/20171216094632/public/ckeditor_assets/pictures/93/content_Screen_Shot_2018-01-11_at_2.29.01_PM.jpg" style="width: 200px; height: 150px; border-top-left-radius: 10px; border-top-right-radius: 10px; border-bottom-right-radius: 10px; border-bottom-left-radius: 10px;" title="PMDM 30: A few downy mildew resistant plants have been found in a pearl millet germplasm line that is otherwise highly susceptible to the disease. The white parchment bags on the panicles of the resistant plants indicate that the plant breeding process is underway to produce a downy mildew resistant version of this pearl millet accession." />
- Fig 30: White parchment bags on the panicles of the resistant plants
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- - <img alt="" src="https://s3.amazonaws.com/plantvillage-production-new/ckeditor_assets/pictures/161/content_PV_PMDM_Fig_32.jpg" style="width: 300px; height: 201px;" /><img alt="" longdesc="Rob Williams" src="//s3.amazonaws.com/plantvillage-production/var/www/sites/production.plantvillage.org/releases/20171216094632/public/ckeditor_assets/pictures/94/content_Screen_Shot_2018-01-11_at_2.29.14_PM.jpg" style="width: 200px; height: 150px; border-top-left-radius: 10px; border-top-right-radius: 10px; border-bottom-right-radius: 10px; border-bottom-left-radius: 10px;" title="PMDM 31: Shows the result of selection within a highly PMDM susceptible line can produce a highly resistant version of that line." />
- + <img alt="" src="https://s3.amazonaws.com/plantvillage-production-new/ckeditor_assets/pictures/172/content_PV_PMDM_Fig_31.jpg" style="width: 300px; height: 205px;" /><img alt="" longdesc="Rob Williams" src="//s3.amazonaws.com/plantvillage-production/var/www/sites/production.plantvillage.org/releases/20171216094632/public/ckeditor_assets/pictures/94/content_Screen_Shot_2018-01-11_at_2.29.14_PM.jpg" style="width: 200px; height: 150px; border-top-left-radius: 10px; border-top-right-radius: 10px; border-bottom-right-radius: 10px; border-bottom-left-radius: 10px;" title="PMDM 31: Shows the result of selection within a highly PMDM susceptible line can produce a highly resistant version of that line." />
- Fig 31: Selection within a highly PMDM susceptible line 
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- 1.3 Can downy mildew resistance be identified in the laboratory or greenhouse?
- A glasshouse screening technique has been developed in which potted seedlings are inoculated at the coleoptile stage with a suspension of sporangia and kept in high humidity at about 25 C for infection and disease development. The technique is precise, independent of the season, and both time-efficient and cost-effective. The technique has been used to screen breeding lines for resistance to downy mildew and to study pathogenic variability within the pearl millet pathotype.
- 1.4 What progress has been made in finding and using host-plant resistance to pearl millet downy mildew?
- In the ICRISAT Pearl Millet Improvement Programme more than 3,100 pearl millet germplasm accessions from about 25 countries were screened for resistance to downy mildew in the period from 1977 to 1992, and 428 accessions were detected with high levels of downy mildew resistance combined with a flowering time of 45 to 60 days.
- Selected sources of downy mildew resistant pearl millet lines were combined at ICRISAT to produce open-pollinated varieties that were released for cultivation in India. One of these, WC-C75 has been cultivated by Indian farmers since 1983 in nine Indian states covering a total of more than 1 million hectares.
- Selection within downy mildew susceptible accessions and breeding lines that possess desirable traits such as high grain quality, drought tolerance, short stature etc. has enable the development of new downy-mildew resistant versions of those accessions/lines that have then been used to produce valuable downy mildew resistant cultivars and hybrids (see Fig 31)
- In India, the national All India Coordinated Millet Improvement Programme of the Indian Council of Agricultural Research has identified many sources of resistance to downy mildew in pearl millet and used the resistance to develop high-yielding downy mildew resistant hybrids and cultivars. These have been multiplied and distributed to farmers through the national seed production system and also by indigenous private sector seed companies.
- In West Africa, ICRISAT in collaboration with the Institute National d'Etude et de Recherche Agricole (INERA) in Burkina Faso has developed several promising downy mildew resistant pearl millet varieties such as the IKMP series.
- 1.5 Have sources of resistance been identified that are effective at locations throughout India and West Africa?
- The International Pearl Millet Downy Mildew Nursery (IPMDMN), coordinated by ICRISAT in cooperation with scientists in national research programmes enabled the screening of pearl millet lines for stability of resistance at many locations in West Africa and India over several years. More than 50 pearl millet lines were identified with stable downy mildew resistance across locations and years. Many of these lines originated from northern Nigeria.
- In West Africa a regional downy mildew screening programme, the West African Downy Mildew Nursery, testing pearl lines contributed by national research scientists at disease "hot spots", identified pearl millet lines with resistance that was effective across the region.
- 1.6 Is there evidence of resistance "breakdown" by new pathogenic races when resistant cultivars are widely grown?
- In India, some downy mildew resistant F1 hybrids, which are genetically uniform, have become susceptible to the disease after their widespread use, as the pathogen has responded to the selection pressure of the resistance.
- In contrast, the genetically diverse open-pollinated pearl millet cultivars such as WC-C75 have retained their downy-mildew resistance when grown widely for several years over large areas. It is assumed that the genetic heterogeneity of open-pollinated varieties provides a buffering against virulence shifts by the downy mildew pathogen. These varieties will not remain totally disease free, but neither is it likely that damaging epidemics of downy mildew will develop.
- 1.7 What strategies are recommended for the use of downy mildew resistant pearl millet F1 hybrids, to avoid resistance breakdown?
- The deployment of a single F1 hybrid for several years over a large area is likely to lead to the breakdown of the resistance.
- Recommendations to avoid resistance breakdown of the F1 hybrids include:
- i. grow several genetically different hybrids at the same time within a region;
- ii. deploy different hybrids sequentially over time.
- For these strategies to be effective several desirable hybrids with different resistance genotypes must be available and there would need to be a co-ordinated system of seed production and distribution servicing an informed community of farmers.
- 1.8 What is "recovery resistance" to downy mildew in pearl millet?
- Research at ICRISAT has identified pearl millet lines in which infected young plants appear to outgrow the pathogen and produce normal grain-bearing heads. This phenomenon has been termed recovery resistance. Selection within pearl millet lines demonstrating some plants with apparent recovery resistance has produced lines with up to 95% of the plants which although infected and showing symptoms of the disease at the vegetative stage go on to develop normal grain-bearing panicles. The value of this recovery resistance is not clear though it has been theorised that the use of such recovery resistance in F1 hybrids may enable the prolonged use of the hybrids with a to reduce risk of resistance breakdown.
- 1.9 From where are resistant varieties available?
- High-yielding downy mildew resistant cultivars of pearl millet have been developed by ICRISAT (http://explorer.icrisat.org/page/pearl_millet/680/275) and several national agricultural research organisations, as well as by private-sector seed companies. Growers wanting access to these cultivars need to contact the national agricultural research and extension services in their country for advice on availability and use strategies.
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- 2. Fungicide Seed Treatment
- 2.1 Can fungicide seed treatment control pearl millet downy mildew?
- Complete control of pearl millet downy mildew can be achieved even in highly susceptible cultivars by seed treatment with appropriate fungicides (Fig 32).
- 2.2 Which fungicides are effective as seed treatments for controlling pearl millet downy mildew?
- High levels of control of pearl millet downy mildew have been achieved by seed treatment with fungicides containing the active ingredients metalaxyl (e.g Apron SD 35) and mefenoxam (e.g Apron XL).
- The active ingredients metalaxyl and mefenoxam move systemically within plants grown from treated seed which makes them ideal for the control of the systemic pearl millet downy mildew.
- Apron 35 SD has been highly effective when applied at the rate of 2 g active ingredient per kg seed. The treatment process is simple and only small quantities of the fungicide are needed.
- The fungicides based on metalaxyl and mefenoxam are patented and registered for use by Syngenta Crop Protection from where further information on the products, where they are registered for use, their environmental impact etc. can be obtained.
- Effective control of pearl millet downy mildew has also been reported on an experimental basis by seed treatment with a formulation (Melody® Duo) of the fungicide active ingredient Iprovalicarb. However, it is registered and recommended for use only as a foliar spray in potato and grape crops. There are reports of downy mildew control with foliar sprays of systemic fungicides, particularly those containing metalaxyl as the active ingredient. However, the use of foliar sprays has no advantage over seed treatment in terms of level of control achievable, and has several disadvantages in that it requires the farmer to have spraying equipment and the means to make up the spray at the correct concentration, it exposes the farmers and the environment to spray drift and contamination, and it is likely to be more expensive.
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- <img alt="" src="https://s3.amazonaws.com/plantvillage-production-new/ckeditor_assets/pictures/162/content_PV_PMDM_Fig_32.jpg" style="width: 300px; height: 201px;" /><img alt="" longdesc="Rob Williams" src="//s3.amazonaws.com/plantvillage-production/var/www/sites/production.plantvillage.org/releases/20180123061925/public/ckeditor_assets/pictures/96/content_Picture1-min.png" style="width: 200px; height: 150px; border-top-left-radius: 10px; border-top-right-radius: 10px; border-bottom-right-radius: 10px; border-bottom-left-radius: 10px;" title="PMDM 32: The complete control of downy mildew in the highly susceptible pearl millet hybrid NHB3 by seed treatment with a metalaxyl containing fungicide (left) with two severely diseased rows growing from untreated seed alongside (right). " />
- Fig 32: Difference between treated and untreated seeds
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- 3. On-farm Actions for Integrated Pathogen Management (IPM)
- 3.1 What do farmers need to take effective on-farm actions?
- Knowledge is the Key. If farmers have information on the nature of the factors adversely affecting their crop, how these factors damage the crop and what is known on how to reduce the damaging effects, then the farmers will be able to find ways that work for them, using the resources available to them within their operating environment. This leads to locally-effective and achievable Integrated Pathogen Management (IPM).
- 3.2 What actions can farmers take to reduce the problem of pearl millet downy mildew?
- The key on-farm actions that farmers can take are sanitation and selection.
- a) remove downy mildew diseased plants from the crop as soon as they are detected;
- b) ensure grain is not threshed with diseased plant parts;
- c) ensure seed for next year's crop is selected from robust disease-free plants.
- 3.3 What are the benefits of removing downy mildew diseased plants?
- a) reduce secondary spread: The Secondary spread of downy mildew within a crop is caused by the spores produced on the leaves of diseased plants, so removal of diseased plants or tillers at the first sign of disease will reduce secondary spread within the crop;
- b) reduce oospore reservoir in soil: As oospores form in diseased plant parts and get into the soil from diseased crop residues, removal of diseased plants from fields at the earliest opportunity not only reduces the secondary spread within the crop but also reduces the oospore "bank" or reservoir in the soil, which will reduce the incidence of primary infection in subsequent seasons;
- c) prevent oospore contamination of seed: when grain is threshed in the presence of diseased leaves and panicles, oospores are released to contaminate the grain, so removal of diseased plants reduces oospore contamination of seed;
- d) delay the build-up of new pathogenic races: the selection pressure imposed by the use of highly downy-mildew resistant cultivars can result in the emergence and spread of new pathogenic races of the pathogen capable of overcoming the resistance, so removal of diseased plants at the earliest opportunity will delay the build-up of the new pathogenic race(s) within the local pathogen population;
- e) delay the build-up of resistance to fungicides: downy-mildew plant pathogens are capable of responding to the selection pressure of the use of highly effective fungicides by developing pathotypes that are able to resist the fungicide, so removal of diseased plants in a crop grown from fungicide-treated seed will delay the build-up of new fungicide-resistant pathogenic race(s) within the local pathogen population;
- f) reduce downy mildew susceptibility levels in local cultivars: pearl millet is highly cross-pollinated, so pollen from diseased plants can be dispersed widely within the crop to fertilise non-diseased plants; removal of diseased plants prior to flowering (emergence of the grain-bearing heads) prevents the pollen from those plants perpetuating and spreading susceptibility within the gene-pool of the local cultivars;
- 3.4 How can farmers increase levels host-plant resistance to pearl millet downy mildew in their local cultivars?
- Farmers can increase the levels of downy mildew resistance in their local cultivars by:
- i. removing downy mildew diseased plants before the plants flower, so that they do not receive pollen to produce seed and do not produce pollen to fertilize other plants:
- ii. collecting seed to be used for sowing next year's crop from disease-free plants
- These actions should reduce the level of susceptibility in the local cultivars gene pool, and lead to the development of a population of locally downy-mildew resistant cultivars.
- 3.5 Why is community action beneficial for the control of pearl millet downy mildew?
- Integrated pathogen management will be more effective if done on a community basis rather than by individual farmers acting alone, as sporangia causing secondary spread and pollen from diseased plants can be carried to neighbors' fields.
- The basis for effective on-farm actions is for all the farmers in the community to fully understand the biology and epidemiology of pearl millet downy mildew and work together to reduce the levels of the disease.
- 3.6 Summary of Options for Integrated Management of Pearl Millet Downy mildew
- • Grow cultivars that are resistant to the pathogen
- • Use appropriate systemic fungicide seed-treatments
- • Practise on-farm sanitation to: a) reduce secondary spread; b) reduce oospore reservoir in soil; c) prevent oospore contamination of seed; d) delay build-up of pathotypes that can break down resistance and resist fungicides; e) build up resistance levels in local cultivars. 
Edited by at November 9, 2018 11 : 34 : 24