EPWS 310 - PLANT PATHOLOGY

LECTURE 13: ASCOMYCETES

Canker and Anthracnose Diseases

Anthracnose Diseases Caused by Colletotrichum

Readings:  Pages 473-500

Southern corn leaf blight - Cochliobolus heterostrophus (teleomorph) and Bipolaris (anamorph)

Causes small tan leaf lesions which may be numerous enough to cover the leaf. The head and ears may also be affected resulting complete loss. The susceptible Texas cytoplasm from race "T" caused the loss of 15% of corn in early 1970's.

Resistance has kept the disease under control but it is widespread.

LIFE CYCLE - Fig. 11-63

Overwinter as conidia and mycelium in plant debris.

Control by resistance and sanitation, rotation and proper break down of plant debris. The fungi do not survive well in intimate contact with soil. So plow the debris in!

SOIL INVADERS v.'s SOIL INHABITANTS

Systemic fungicides as Imazalil, Nuarimol and Fenapenil work well for both the foliar and root phases of these diseases.

CANKER AND ANTHRACNOSE DISEASES

Nectria canker diseases

Ascomycete Anamorph is Fusarium and Cylindrocarpon.

Major disease of apples and pears and forest hardwoods.

Cankers girdle the tree and can kill saplings while lopping branches off older trees.

These are necrotrophic and enter through wounds and bud scars. The spores are dispersed by rain and insects.

Typified by callus growth and target shaped cankers.

LIFE CYCLE - Fig. 11-70

Conidia formed on sporodochia and overwintering as mycelium in dead bark and callus tissue and as perithecia in bark.

Ascospores are abundant in late fall.

Control: Sanitation and burning of affected limbs and fungicide application after leaf fall reduced inoculum in orchards.

ANTHRACNOSE DISEASES CAUSED BY COLLETOTRICHUM

There are many anthracnose fungi but the most common and important is Colletotrichum anamorph of Glomerella. These form a complex of diseases of many crops and ornamentals - Rose, strawberry, grape, raspberry, citrus, apple soybean, banana, cotton, hickory etc etc.

Including the Diplocarpon black spot of rose.

Generally a problem under humid conditions cool to warm, often bad in greenhouses.

The diseases often affect young tissue, leaves, shoots, flowers etc.

They are often seedborne.

They are unusual fungi in that the early stages of infection are biotrophs and then necrotrophs. Often with latent infection.

Colletotrichum affects cucurbits, tomato, cereals, grasses, banana, onion and citrus.

LIFE CYCLE Fig. 11-84

Favored by warm humid conditions.

Control depends on disease free seed and sanitation, some resistance is available. Fungicides applied as control and postharvest.

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