نام فایل : بيماري‌هاي cucumber 20 اسلاید (3)

فرمت : .ppt

تعداد صفحه/اسلاید : 20

حجم : 914 کیلوبایت

عنوانبيماري‌هاي cucumber
استاد:
آقاي دكتر نصرالله نژاد
دانشجويان:
كيانا كبير ـ اكرم كياني
Powdery Mildew
caused by the fungus Erysiphe cichoracearum, affects cucumber, muskmelon, pumpkin, and squash. It is caused by a fungus that appears as a white powdery growth on leaves. Crown leaves are affected first and may wither and die. The fungus can be introduced on greenhouse-grown plants or by wind from areas with relatively warm winter climate where the fungus can over-winter. Disease development is favored by high temperatures.
Downy Mildew
on cucumber and muskmelon is caused by the fungus Pseudoperonospora cubensis. Irregularly shaped yellowish to brown spots appear on upper sides of leaves, usually at the center of plants. Under moist conditions, a purplish mildew develops on the underside of leaf spots. Leaves die as spots increase in size. Spread is rapid from the crown toward new growth. The causal fungus overwinters in areas with a relatively warm climate and can be introduced to other areas by wind. Moist conditions favor disease development.
Target Spot
caused by Corynespora cassiicola, is similar to downy mildew in appearance. Leaf spots begin as small yellow flecks which become angular or as circular spots with light brown centers and dark brown spots. Spots vary from 1/8 to 3/8 inch in diameter. Lesion coalescence may result in large areas of dead tissue, which may shred and fall out.
Cercospora Leaf Spot
caused by Cercospora citrullina, affects cantaloupe and watermelon. Leaf spots are small, dark brown to black with a white center, and may have a yellow halo.
Alternaria Leaf Spot
caused by the fungus Alternaria cucumerina, occurs primarily on muskmelons but also on cucumbers and other cucurbits. Leaf spots are small, circular, and water-soaked at first, and then expand up to 1/2 inch in diameter with dark concentric rings within the spots. Spots coalesce to affect large areas of leaves and cause defoliation that begins on crown leaves. This disease-causing fungus overwinters on and in seed, as well as in residue from diseased plants. Fungus spores (reproductive structures) are spread by wind, by running and splashing water, on workers, and on tools and implements. Weak and senescing plants are more susceptible to Alternaria leaf spot than are vigorous plants.
Anthracnose
caused by the fungus Colletotrichum lagenarium, affects cucumbers, muskmelons, and watermelons. Muskmelon and cucumber leaf spots begin as yellowish or water-soaked areas that enlarge rapidly, turn brown, and shatter to form a ragged hole within the spot. Leaf spots on watermelons turn black. Elongated dark spots with light centers often develop on petioles and stems and can cause death of tissue beyond these spots. Young fruit may be killed, but large fruit usually develop depressed dark-bordered cankers with creamy pink colored ooze in the center. The fungus overwinters in seed and in residue from diseased plants, and is spread in splashing water. Humid weather and frequent rains promote disease development and spread.
Angular Leaf Spot
caused by the bacterium Pseudomonas lachrymans, affects cucumber, squash, and pumpkin and is characterized by conspicuous leaf symptoms. Stem and fruit symptoms occur, but are less conspicuous. Leaf spots are angular and irregular in shape and size. spots, water-soaked at first, later turn gray or tan and finally drop out, leaving ragged holes. Fruit infections appear as small sunken water-soaked spots; fruit rot soon follows. Bacteria which cause this disease overwinter on seed and persist in crop residue from diseased plants. Splashing rain and workers spread the bacterium within fields.
Scab
....