7-2 Solanceous Fruits Diseases

1. 7-2 Solanceous Fruits Diseases

2. 7.2.1 Tomoto Leaf Mould • Leaf mould is a disease of tomatoes only. • The disease is a common and destructive disease on tomatoes worldwide grown under humid conditions. • Leaf mold is primarily a problem on greenhouse tomatoes, but occasionally develops on field and garden-grown tomatoes if conditions are favorable. • he disease is most destructive in the greenhouse during the fall, early winter, and spring when the relative humidity is most likely to be high, and air temperatures are such that heating is not continuous.

3. Tomoto Leaf Mould • When humidity is high, the fungus develops rapidly on the foliage, usually starting on the lower leaves and progressing upward. • If the disease is not controlled, large portions of the foliage can be killed, resulting in significant yield reductions. • Early infections are most threatening.

4. Symptoms • Major symptoms occur on the foliage but they may also occur on petioles（叶柄）, stems, and fruit peduncles（果梗） (but not on the fruit itself). • All stages of growth are attacked.

5. Symptoms • The first leaf symptom is the appearance of small, white, pale green, or yellowish spots with indefinite margins on the upper leaf surface. • On the corresponding areas of the lower leaf surface the fungus begins to sporulate. • The fungus appears as an olive green to grayish purple velvety growth composed mostly of spores (conidia) of the leaf mold fungus.

6. Symptoms • Infected leaf tissue becomes yellowish brown, and the leaf curls, withers, and drops prematurely. • The withering and defoliation progress up the plant until the entire plant may appear dry and dead. • Disease development is slow and severe symptoms are usually present only late in the season; however, major yield losses are possible if infection occurs early. • Seed-borne infection has not been reported.

8. Pathogen Fulvia fulva，synonym Cladosporium fulvum Spores germinate in water films or when humidity levels are above 85 percent, at temperatures between 4 and 34℃. The optimum temperature for germination is between 24 and 26 ℃.

10. Disease Cycle • The fungus survives between seasons as conidia (spores), as sclerotia on plant debris, in seed, and as a soil saprophyte. • Conidia are resistant to drying, and may survive in the greenhouse at least 1 year in the absence of a susceptible host, and new conidia can be produced from surviving sclerotia. • The conidia act as primary inoculum to infect plants when conditions become favorable.

11. Disease Cycle • Leaves are infected through stomata when humidity levels are 85 percent or higher. • Infection occurs most rapidly when humidity levels at the leaf surface fluctuate between 85 percent (day) and 100 percent (night). • Symptoms usually begin to appear approximately 10 days after inoculation, with spore formation beginning a few days later. • Spore production is most abundant at relative humidity between 78 and 92 percent, but can occur at humidity as low as 58 percent.

12. Conditions for Disease Development • Many cycles of disease development are possible during the growing season. • Disease development is influenced by temperature, relative humidity, and long periods of leaf wetness. • The presence of moisture on the foliage from dew, rainfall and fog provides good conditions for disease development. • Increasing periods of leaf wetness are associated with increasing disease severity; consequently, the disease may become more serious during the rainy season when warm temperatures prevail. I • ts spores will not germinate if the relative humidity is less than 85%.

13. CONTROL • 1. Whenever possible, keep the relative humidity in the greenhouse below 85 percent. This will inhibit the development and spread of the leaf mold fungus. • Provide good ventilation and as much light as possible. • b. Attempt to avoid wetting the leaves when watering. Water early in the day to allow leaves to dry by mid-afternoon.

14. CONTROL • c.Maintain a temperature of at least 16 to 18℃ throughout the season. • d.Provide adequate plant and row spacing to avoid excessive shading.

15. CONTROL 2. Leaf mold resistant varieties are available, but because the fungus mutates readily (there are at least 12 races of the pathogen) resistant varieties are of limited use. Because new virulent races can develop in only a few years, a tomato variety which is resistant one year may be very susceptible the next. If available, grow varieties with more than one leaf mold resistance gene.

16. CONTROL 3. A fungicide spray program may help control the disease, but should be considered secondary to environmental control measures. A weekly spray program may be necessary. For current recommendations refer to the above mentioned circular. Be sure to thoroughly cover all aboveground parts of every plant, especially the lower surface of the foliage, with each spray.

17. CONTROL 4. Reduce primary inoculum levels through sanitation, steam treatment of greenhouses, and seed treatment. a. After harvest, carefully remove and destroy (burn) all plant debris. b. Where possible, steam entire greenhouse sections between crops, preferably on a bright, hot day when little steam will be needed. Close all ventilators, and maintain the temperature at 57℃ for at least six hours. c. Where necessary, use hot water treated seed. Treat seed for 25 minutes at exactly 50℃.

18. 小结 发生概况：分布？ 危害？产量损失 病害识别：发病时期？症状特点？ 病原：分类地位；生物学特性 病害发生发展规律：越冬、传播、入侵方式 发病及其影响因素：气象因素（温暖、高湿）；栽培管理；寄主抗病性 综合防治：选用抗病品种；种子消毒；加强栽培管理；合理生态管理；消灭菌源；化学防治

19. 7.2.2 Early blight of tomato

20. Significance • Early blight of tomato, caused by the fungus Alternaria solani, is perhaps the most common foliar disease of tomatoes in the Northeast and is also common on potatoes. This disease causes direct losses by the infection of fruits and indirect losses by reducing plant vigor. Fruit from defoliated plants are also subject to sunscald.

21. Symptoms • Early blight produces a wide range of symptoms at all stages of plant growth. It can cause damping-off, collar rot, stem cankers, leaf blight, and fruit rot. The classic symptoms occur on the leaves where circular lesions up to 1/2" in diameter are produced. Within these lesions dark, concentric circles can be seen. The leaf blight phase usually begins on the lower, older leaves and progresses up the plant. Infected leaves eventually wither, die, and fall from the plant.

24. Pathogen • Alternaria solani (Ellis et Martin) Jones et Grout.

25. Disease Cycle • Environmental Conditions • Alternaria spores germinate within 2 hours over a wide range of temperatures but at 80 to 85oF may only take 1/2 hour. Another 3 to 12 hours are required for the fungus to penetrate the plant depending on temperature. After penetration, lesions may form within 2-3 days or the infection can remain dormant awaiting proper conditions (60oF and extended periods of wetness).

26. Disease Cycle • Alternaria sporulates best at about 80oF when abundant moisture (as provided by rain, mist, fog, dew, irrigation) is present. Infections are most prevalent on poorly nourished or otherwise stressed plants.

27. Disease Cycle • Survival and Dispersal • The fungus spends the winter in infected plant debris in or on the soil where it can survive at least one and perhaps several years. It can also be seed borne. New spores are produced the following season. The spores are transported by water, wind, insects, other animals including man, and machinery. Once the initial infections have occurred, they become the most important source of new spore production and are responsible for rapid disease spread

28. CONTROL • Use only clean seed saved from disease-free plants. • Remove and destroy crop residue at the end of the season. Where this is not practical, plow residue into the soil to promote breakdown by soil microorganisms and to physically remove the spore source from the soil surface.

29. CONTROL • Practice crop rotation to non-susceptible crops (3 years). Be sure to control volunteers and susceptible weeds. • Promote good air circulation by proper spacing of plants. • Orient rows in the direction of prevailing winds, avoid shaded areas, and avoid wind barriers. • Irrigate early in the day to promote rapid drying of foliage.

30. CONTROL • Healthy plants with adequate nutrition are less susceptible to the disease. • Minimize plant injury and the spread of spores by controlling insect feeding. • Hand picking diseased foliage may slow the rate of disease spread but should not be relied on for control. Do not work in a wet garden. • Use resistant or tolerant varieties. • The preventative fungicide used on a seven to ten day schedule gives effective control.

31. 小结 发生概况：分布？ 危害？产量损失 病害识别：为害？发病时期？症状特点？ 病原：分类地位；生物学特性 病害发生发展规律：越冬、传播、入侵方式 发病及其影响因素：气象因素（高温、高湿）；寄主的生育期和长势；寄主抗病性 综合防治：选用抗病品种；选用无病种子；加强栽培管理；化学防治

32. 7.2.3 Botrytis blight • Botrytis blight, or gray mold, as it is commonly known, has an exceptionally wide host range with well over 200 reported hosts. • The fungus can occur as both a parasite and a saprophyte on the same wide range of hosts. • This fungus disease is intriguing in that it can cause a variety of plant diseases including damping-off and blights of flowers, fruits, stems, and foliage of many vegetables and ornamentals.

33. Botrytis blight It is a major cause of postharvest rot of perishable plant produce, including tomatoes at harvest and in storage. The disease can occur both in the greenhouse and in the field. Besides tomato, gray mold is of concern to other vegetables including snap and lima beans(菜豆), cabbage, lettuce and endive, muskmelon（香瓜）, pea, pepper, and potato.

34. Symptoms • “Ghost spots” appear on fruits after periods of prolonged high humidity. • These superficial spots have a pale halo with a brown to black pinpoint spot in the center. • On unripe fruit, the halo is pale green or silvery, and generally the tissue inside the halo is paler green. • On ripe fruit, the halo is pale yellow. If warm and sunny weather occurs, then ghost spot symptoms usually do not develop further, although the marketability of the fruit may be affected. Fruit rot does not develop under these specific conditions.

35. Symptoms Botrytis may develop on dying flowers and subsequently infect the fruit calyx. The lesions on fruit appear as light brown to gray spots, up to 3 cm in diameter, and irregular in shape. Later, a dark gray, velvety growth develops on the fruit surface, followed by a watery, soft rot.

36. Symptoms • Foliar symptoms are more common under humid greenhouse conditions. • Affected leaves show light tan or gray spots, and the infected areas become covered by a brown fungal growth. • The leaves wither and collapse. The fungus proceeds into the stem producing tan, elliptical cankers with concentric rings. Invasion of lesions by secondary fungi occurs. Stem cankers cause wilting of vines.

39. Pathogen Gray mold is caused by the fungus Botrytis cinerea. One-celled spores are borne on branched conidiophores, and the arrangement of the spores gives the fungus its name, from the Greek botrys, meaning a bunch of grapes. Use of a hand lens may reveal the characteristic grape-cluster arrangement of spores. As the conidiophores dry out, they gently move and liberate the spores: usually air movements are sufficient to get the spores airborne.

41. Pathogen The fungus often establishes itself on injured tissues and can persist as a saprophyte for long periods. Upon occasion, black sclerotia of variable size form on or just below, the host surface. The sclerotia have a black rind and a light interior composed of a dense mass of hyphae, or threads, of the fungus. Sclerotia measure up to 3 mm (occasionally 5 mm) in length and are usually smaller and thinner than those of the white mold fungus Sclerotinia sclerotiorum.

42. Pathogen The sclerotia germinate to produce conidiophores or, rarely, give rise to small cup-shaped structures (apothecia), which are the sexual stage of the fungus. Sclerotia are resistant to environmental extremes and act as overwintering resting bodies.

43. Disease Cycle • The fungus overwinters as sclerotia or as mycelium in plant debris and may be seedborne as spores or mycelium in a few crops. • Other crops may also serve as sources of the pathogen and are likely to cross-infect. • The fungus is easily dispersed large distances by wind. Small pieces of infected plant tissue or fungal spores from infected plant debris are also disseminated shorter distances by splashing and windblown rain. High relative humidities are necessary for prolific spore production.

44. Disease Cycle In the field, spores landing on tomato plants germinate and produce an infection when free water from rain, dew, fog, or irrigation occurs on the plant surface. Optimum temperatures for infection are between 18 and 24℃, and infection can occur within 5 hours. High temperatures, above 28℃, suppress growth and spore production.

45. Disease Cycle Dying flowers are a favorable site for infection, but infections can also result from direct contact with moist infested soil or plant debris. In the greenhouse, stem lesions develop either by direct colonization of wounds or through infected leaves. The presence of external nutrients, such as pollen grains in the infection droplet, can markedly increase infection.

46. Disease Cycle The type of wound is said to influence stem lesion development; breaking off leaves is reported to give a lower incidence of stem lesions than cutting off leaves with a knife, leaving a stub.

49. Conditions for Disease Development • The fungus has a very wide host range that includes many vegetable crops. • Gray mold development, particularly fungus • sporulation and infection, is favored by cool, wet and humid weather. • The fungus requires a water film of several hours for spore germination, and a longer period of surface wetness for symptom development.

50. Conditions for Disease Development • Optimum relative humidity for spore production is about 90%, and most spores are produced during the night when the temperature is lower and the relative humidity is higher than during the day. • Temperatures of 17–23℃ are ideal for disease development. The length of the surface wetness period needs to be longer at the lower temperatures for disease development.