Plant Pathology L7

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1.     Vascular wilt

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1.     Fusarium wilt of tomato

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Pathogens:

Ceratocystis, Ophiostoma, Fusarium, and Verticillium.

Ceratocystis- vascular wilt of oak trees (C. fagacearum), cacao, and of eucalyptus.

Ophiostoma -Dutch elm disease (O. novo-ulmi).

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Fusarium: vegetables and flowers, herbaceous perennial ornamentals, plantation

crops, and the mimosa tree (silk tree)

Verticillium vegetables, flowers, field crops, perennial ornamentals, and fruit and forest trees.

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Control

 Use of varieties resistant

 Seedbed sterilization and crop rotation

Soil sterilization for green house

Use of healthy seed and transplants

Biological control

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Disease cycle

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Botrytis cinerea

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Botrytis rot

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Southern corn blight

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Bipolaris maydis

(also known as Cochliobolus heterostrophus)

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Host:

strawberry, blackberry, grape, raspberry

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Pathogen can colonize most host tissues including flowers, fruit, leaves, runners (stolons), and shoots

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Pathogen can be classified into three races: Race O, Race C, and Race T. Race O, which can infect normal cytoplasm varieties of maize and produces symptom in

the form of leaf lesions. Lesions are tan, somewhat rectangular in shape, and have reddish-brown margins

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Race T produce T-toxin. Corn with Texas male sterility cytoplasm is susceptible. Race T attacks leaves, husks, stalks, leaf sheaths, shanks, ears, and cobs.

Race T lesions are rectangular to elliptical (¼ to ½ inch wide by ¼ to ¾ inch long) with a reddish-brown border that may be surrounded by a chlorotic zone. Stalk and leaf infections initially appear as purple spots that develop tan-gray centers.

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Ear infections result in a gray-black lesion on the husk that extends into the kernels, appearing as a black felt-like mold.

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Affected kernels are covered with a black, felty mold, and cobs may rot or, if the shank is infected early, the ear may be killed prematurely and drop. Seedlings from infected kernels may wilt and die within a few weeks of planting.

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Infected tissues turn light to medium brown in color, and under high relative humidity become covered in a velvety, grayish-colored mass of fungal mycelium. Fruits become soft and water soaked. This mycelium produces branched structures called conidiophores, which in turn produce numerous microscopic asexual spores referred to as conidia.

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If humidity is low, infections may not sporulate and tissues remain brown, shriveled, and leathery.

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Direct infection may also occur on ripe fruit if conidia land on wounded tissue, resulting from insect predation, or physical contact with neighboring fruit or hard detritus on the planting floor.

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A hardened, black (melanized), oblong structure called a sclerotium (plural: sclerotia) may also form on severely infected tissues when nutrients are exhausted and temperatures cool. This resistant structure allows the fungus to overwinter more effectively than as mycelium in plant tissues.