Tomato

Description

Tomato, Lycopersicum esculentum (syn. Solanum lycopersicum and Lycopersicon lycopersicum) is an herbaceous annual in the family Solanaceae grown for its edible fruit. The plant can be erect with short stems or vine-like with long, spreading stems. The stems are covered in coarse hairs and the leaves are arranged spirally. The tomato plant produces yellow flowers, which can develop into a cyme of 3–12, and usually a round fruit (berry) which is fleshy, smoothed skinned and can be red, pink, purple, brown, orange or yellow in color. The tomato plant can grow 0.7–2 m (2.3–6.6 ft) in height and as an annual, is harvested after only one growing season. Tomato may also be referred to as love apple and originates from South America.


Uses

Tomato fruit can be eaten raw or cooked and is used in many dishes. The fruit may also be processed into juice, soup, ketchup, puree, paste or powder.


Propagation

Requirements Tomatoes grow very well in warm areas at temperatures between 21 and 24°C (69.8–75.2°F). They require a deep, loamy, well-draining soil with a pH between 5.5 and 6.8. If soil drainage is a problem then tomatoes can be planted in a raised bed. Like all fruiting plants, tomatoes require full sun for most of the day. Tomato varieties Determinate (“bush”) tomatoes have been purposefully bred to grow vertically and remain relatively compact. The plant will stop growing once fruit begins developing on the terminal shoot and all the fruits ripen at around the same time. In contrast, indeterminate (“vining”) tomato varieties spread laterally and will continue to grow and produce fruit until frosts begin the the Fall. Indeterminate varieties can produce fruit all season and fruits will develop and ripen at different times. Heirloom tomatoes are generally open-pollinated varieties which have been conserved over many generations due to certain desirable characteristics such as flavor. Hybrid tomatoes are the product of cross-pollination between two parents with desirable characteristics such as high yield, early maturation, improved flavor or resistance to certain diseases. Sowing seeds In most cases, tomato seeds should be started indoors 6–8 weeks before last Spring frost. Seeds can be direct seeded in areas with a long growing season. Seeds should be sown in flats or cell trays using a sterile seedling mix. Plant seeds to a depth of 0.6 cm (1/4 in) and water lightly. If cells are being used, plant several seeds in each cell and thin to 1 seedling after germination. Position trays in a bright South facing window or under fluorescent lighting. The optimum soil temperature for germination is 21–32°C (70–90°F). A heat mat can be used to warm the flats if required. Seedlings should emerge within 6-14 days and after the seedlings has developed the first set of true leaves then they can be moved to a larger (3-4 in) pot and moved to a cooler temperature (16–21°C/60–70°F). Transplanting Tomato seedlings are ready to be transplanted once they are 15–25 cm (6–10 in) in height and have 3–5 true leaves assuming all danger of frost has passed. Beginning approximately 7-10 days before transplanting, plants should be set outside to harden off (see https://www.plantvillage.com/posts/264). The transplanting site should be prepared by working in a balanced fertilizer according to the guidelines on the product label. Transplants should be spaced 76–123 cm (30–48 in) apart with a between row spacing of 123 cm (48 in). It is common practice to plant tomatoes in trenches on their side (see https://www.plantvillage.com/posts/833-tomato) as tomato stems will sprout roots along their length when buried. Avoid over-fertilizing transplants, particularly with nitrogen, at this stage of growth as it will promote growth of foliage rather than fruits. Water plants lightly at base instead of overhead as wet foliage is more prone to diseases and the buried stem needs time to adapt and sprout roots. It is important that tomato plants receive even watering to prevent the development of blossom end rot, drip or soaker hoses work best and mulching around the plants helps to conserve soil moisture. Stakes, Cages and Trellises Staking, caging or trellising tomatoes supports the plants and helps to keep fruit off of the ground as well as increasing air circulation around the foliage which helps to prevent disease. The type of support system used depends on the type of tomatoes being grown. Determinate tomatoes have short or medium length vines and stop growing once fruit develops on the terminal branches. Determinates can be staked or caged but do not adapt to trellises. The position of the fruit means that little heavy pruning is required. In contrast, indeterminate tomatoes grow indefinitely and require a support system to prevent them trailing along the ground. The amount of pruning required depends on the support system being utilized - vines require only light pruning when caged, moderate pruning when staked and heavy pruning when using a trellis.


References

AVRDC Publication 04-609 (2004). Tomato mosaic virus (ToMV). AVRDC. Available at: http://203.64.245.61/web_crops/tomato/ToMV.pdf. [Accessed 22 April 15]. Free to access. CABI Crop Protection Compendium. (2013). Solanum lycopersicum (tomato) datasheet. Available at: http://www.cabi.org/cpc/datasheet/31837. [Accessed 09 February 14]. Paid subscription required. Jones, J. P., Stall, R. E. & Zitter, T. A. (1991). Compendium of Tomato Diseases. American Phytopathological Society Press. Available for purchase from APS Press. Kopsell, D. (2000). Growing tomatoes. University of New Hampshire Cooperative Extension. Available at: http://extension.unh.edu/resources/files/resource000609_rep631.pdf. [Accessed 09 February 15]. Free to access Lerner, B. R. Tomatoes. Purdue University Cooperative Extension. Available at: http://www.hort.purdue.edu/ext/HO-26.PDF. [Accessed 09 February 15]. Free to access U-Scout (2014). Tomato diseases. Plant Pathology Lab, NFREC. University of Florida Cooperative Extension. Available at: http://nfrec.ifas.ufl.edu/paret/u-scout/Tomato/Tomato.html. [Accessed 09 February 15]. Free to access











Common Pests and Diseases

Diseases

Category : Fungal

Anthracnose Colletotrichum coccodes

Symptoms
Fruit symptoms are the most common although stem, leaves and roots can also be infected; disease causes characteristic sunken circular lesions on the fruit; the indentations on may have visible concentric brown and yellow rings; lesion centers turn tan in color as they mature and become dotted with small black fungal fruiting bodies (microsclerotia); lesions can grow very large
Cause
Fungus
Comments
Disease emergence favors warm weather; appears early in the spring
Management
Avoid sprinkler irrigation when fruit is ripening; rotate crops with other non-solanaceous plants

Black mold Alternaria alternata

Symptoms
Disease causes the appearance of black or brown lesions on the surface of ripe fruit; lesions may be tiny flecks or may be large patches of decaying tissue; during periods of humid weather, the lesions may become covered in black, velvety spore masses.
Cause
Fungus
Comments
Disease is found wherever tomatoes are grown; ripe fruit become increasingly susceptible to the fungus the longer they stay on the vine after ripening.
Management
Cultural control methods such as avoiding wetting the foliage when watering and harvesting fruits as soon as they are ripe can help to reduce the incidence of the disease; in areas where disease is a persistent problem, chemical control may be necessary with an appropriate fungicide; fungicide is usually applied 4-6 weeks prior to the first anticipated fruit harvest.

Early blight Alternaria solani

Symptoms
Early blight symptoms start as oval shaped lesions with a yellow chlorotic region across the lesion; concentric leaf lesions may be seen on infected leaves; leaf tissue between veins is destroyed; severe infections can cause leaves to completely collapse; as the disease progresses leaves become severely blighted leading to reduced yield; tomato stems may become infected with the fungus leading to Alternaria stem canker; initial symptoms of of stem canker are the development of dark brown regions on the stem; stem cankers may enlarge to girdle the whole stem resulting in the death of the whole plant; brown streaks can be found in the vascular tissue above and below the canker region; fruit symptoms include small black v-shaped lesions at the shoulders of the fruit (the disease is also known black shoulder); lesions may also appear on the fruit as dark flecks with concentric ring pattern; fruit lesions can seen in the field or may develop during fruit transit to the market; the lesions may have a velvety appearance caused by sporulation of the fungus
Cause
Fungus
Comments
Disease can spread rapidly after plants have set fruit; movement of air-borne spores and contact with infested soil are causes for the spread of the disease
Management
Apply appropriate fungicide at first sign of disease; destroy any volunteer solanaceous plants (tomato, potato, nightshade etc); practice crop rotation

Fusarium wilt Fusarium oxysporum

Symptoms
Symptoms of Fusarium wilt may first appear as yellowing and wilting of leaves on one side of the leaf midrib or plant; one-sided symptoms are caused by a blockage in the vascular system supplying the symptomatic side of the plant; as the disease progresses, older leaves become necrotic and the plant begins to wilt; fruit on infected plants is smaller and yield is reduced; damage to leaves makes fruit susceptible to sunscald; stem symptoms may be mistaken for bacterial wilt but a bacterial ooze test will be negative; stem tissue becomes discolored brown
Cause
Fungus
Comments
Disease emergence favors warm, moist soil Fusarium wilt is not a major issue in tomato production, however, the disease can still cause minor losses
Management
Plant resistant varieties; sanitize all equipment regularly; control root knot nematodes; rotate crops away from tomato for several years

Gray mold (Botrytis blight) Botrytis cinerea

Symptoms
Disease appears on tomato seedlings at or just below the soil line as a fuzzy gray-brown lesion which often girdles the stem, if stem is girdled all parts of the plant above the lesion begin to wilt; infected flowers and calyxes become covered in gray spores; unripe fruit turns light brown or gray in color and rots; green fruit infected by airborne spores develop circular white rings called “ghost spots”.
Cause
Fungus
Comments
Gray mold is usually associated with wounds on plants; can develop in relatively cool conditions.
Management
Liming soil to increase calcium content can help to reduce plant susceptibility to gray mold; application of appropriate fungicide prior to formation of dense canopy.

Leaf Mold Passalora fulva

Symptoms
The older leaves exhibit pale greenish to yellow spots (without distinguishable margins) on upper surface. Whereas the lower portion of this spots exhibit green to brown velvety fungal growth. As the disease progress the spots may coalesce and appear brown. The infected leaves become wither and die but stay attached to the plant. The fungus also infects flowers and fruits. The affected flowers become black and drop off. The affected fruit intially shows smooth black irregular area on the stem end but later it becomes sunken, leathery and dry.
Cause
Fungus
Comments
The disease is favored by high relative humidity. Also a common disease in green house tomato crop.
Management
Grow available resistant varieties. Avoid leaf wetting and overhead application of water. Follow proper spacing to provide good air circulation around the plants. Remove the infected plant debris and burn them. If the disease is severe scary suitable fungicide.

Septoria leaf spot Septoria lycopersici

Symptoms
Symptoms may occur at any stage of tomato development and begin as small, water-soaked spots or circular grayish-white spots on the underside of older leaves; spots have a grayish center and a dark margin and they may colasece; fungal fruiting bodies are visible as tiny black specks in the center of spot; spots may also appear on stems, fruit calyxes, and flowers.
Cause
Fungus
Comments
Spread by water splash; fungus overwinters in plant debris.
Management
Ensure all tomato crop debris is removed and destroyed in Fall or plowed deep into soil; plant only disease-free material; avoid overhead irrigation; stake plants to increase air circulation through the foliage; apply appropriate fungicide if necessary.

Target Spot Corynespora cassiicola

Symptoms
The fungus infects all parts of plant. Infected leaves shows small, pinpoint, water soaked spots initially. As the disease progress the spots enlarge to become necrotic lesions with conspicuous concentric circles, dark margins and light brown centers. Whereas the fruits exhibit brown, slightly sunken flecks in the beginning but later the lesions become large pitted appearance.
Cause
Fungus
Comments
The pathogen infects cucumber, pawpaw , ornamental plants, some weed species etc. The damaged fruits are susceptible for this disease.
Management
Remove the plant debris and burn them. Avoid over application of nitrogen fertilizer. If the disease is severe spray suitable fungicides.

Verticillium wilt Verticillium albo-atrum
Verticillium dahliae

Symptoms
Symptoms appear first on lower leaves and spread upwards; initial symptoms of the disease may be visible as yellow blotches on the lower leaves of the plant; a rapid yellowing of leaves follows as the disease progresses; leaf veins turn brown and brown dead spots appear on the leaves; leaves may wilt then die and drop from the plant; the disease progresses upwards through the stem causing the plant to be stunted; leaves at the top of the plant remain green; fruits develop yellow shoulders and yield is reduced; loss of leaves results in fruit being susceptible to sun scald.
Cause
Fungi
Comments
Fungi survive in crop debris in soil; disease emergence favors cool weather.
Management
Plant resistant varieties; sanitize all equipment on a regular basis; rotate with non-susceptible crops.

Category : Bacterial

Bacterial canker Clavibacter michiganensis

Symptoms
Bacterial canker can affect tomato plants of any age, seedlings may be killed quickly once they become infected; initial symptoms of bacterial canker is the unilateral wilting of plants and formation of light colored streaks up and down the outside of the leaf midrib, petiole and stem; streaks on stems may break open to form cankers; mature leaves develop small necrotic spots on the upper leaf surfaces or small raised white spots on the leaves; white spots develop on fruit, usually while they are still green; spots on fruit develop a raised dark center and are known as "bird's eye spots"
Cause
Bacterium
Comments
Can cause serious crop losses
Management
Plant only certified seed and transplants; hot water treatment of seed to remove bacteria; rotate crops with non-host plants; turn crops into soil after harvest to promote decomposition

Bacterial speck Pseudomonas syringae

Symptoms
Dark specks appear on the leaves, often associated with a yellow halo; foliar symptoms of bacterial speck are very difficult to distinguish from bacterial spot but can be differentiated by symptoms on the fruit; lesions on fruit are much smaller than those caused by bacterial spot; lesions on fruit are raised and scaly.
Cause
Bacterium
Comments
Disease emergence favors cool, moist weather.
Management
Do not plant in same area in successive years; use only high quality, disease-free seed and transplants; protective sprays of copper can help to reduce incidence of the disease.

Bacterial spot Xanthomonas campestris pv. vesicatoria
Xanthomonas euvesicatoria
Xanthomonas perforans = [Xanthomonas axonopodis (syn. campestris) pv. vesicatoria], Xanthomonas vesicatoria
Xanthomonas gardneri

Symptoms
Bacterial spot lesions starts out as small water-soaked spots; lesions become more numerous and coalesce to form necrotic areas on the leaves giving them a blighted appearance; of leaves drop from the plant severe defoliation can occur leaving the fruit susceptible to sunscald; mature spots have a greasy appearance and may appear transparent when held up to light; centers of lesions dry up and fall out of the leaf; blighted leaves often remain attached to the plant and give it a blighted appearance; fruit infections start as a slightly raised blister; lesions may have a faint halo which eventually disappears; lesions on fruit may have a raised margin and sunken center which gives the fruit a scabby appearance.
Cause
Bacterium
Comments
Bacteria survive on crop debris; disease emergence favored by warm temperatures and wet weather; symptoms are very similar to other tomato diseases but only bacterial spot will cause a cut leaf to ooze bacterial exudate; the disease is spread by infected seed, wind-driven rain, diseased transplants, or infested soil; bacteria enter the plant through any natural openings on the leaves or any openings caused by injury to the leaves.
Management
Use only certified seed and healthy transplants; remove all crop debris from planting area; do not use sprinkler irrigation, instead water from base of plant; rotate crops.

Bacterial wilt Ralstonia solanacearum

Symptoms
Initial symptoms of the disease is the wilting of a few of the youngest leaves; the disease progresses rapidly in hot weather and the entire plant wilts suddenly and dies; in cooler conditions, wilting is less rapid and plant may produce roots on the stems; vascular tissue shows a brown discoloration and decaying roots; stems cut under water will ooze bacterial exudate and will confirm the symptoms are not caused by Fusarium wilt.
Cause
Bacterium
Comments
Bacterial wilt can cause complete destruction of the crop under conditions suitable for the spread of the soil-borne bacterium; disease causes serious losses in tomatoes grown in tropical and subtropical regions.
Management
Cultural practices may help to reduce incidence of the disease, rotate tomato with other, non-susceptible crops; avoid over-watering plants.

Category : Other

Blossom-end rot