EPWS 310 - PLANT PATHOLOGY

LECTURE 15: ASCOMYCETES

Root and stem Rots

Fruit and Flower Diseases

Root and Stem Rots

Fusarium, Bipolaris, Phymatotrichum.

Pages 534-546, 550-555

Fruit and flower diseases caused by Claviceps, Venturia and Monilinia.

Flower and fruit diseases.

Pages 501-521

ROOT AND STEM ROTS

Caused by Fusarium, Bipolaris, Gaeumannomyces, Phymatotrichum.

All are common and have very simple life cycles and only somewhat more complex disease cycles. All have some method of survival in soil either as chlamydospores; sclerotia or as encapsulated by host tissue.

These fungi are found worldwide and affect a broad range of hosts.

Fusarium attacks everything (F. solani). Bipolaris is less broad and Gaeumannomyces attacks only cereals. Phymatotrichum is found only in the southwestern US and attacks all dicotyledonous plants.

Gaeumannomyces is the only teleomorph of all these.

Control ?

Fruit and Flower Diseases

These are Ascomycetes

Ergot of Cereals - Claviceps purpurea

Worldwide of historic significance in Europe over the past several hundred years. The most recent outbreaks in Europe were in the central European countries. There are still outbreaks of the disease in developing countries and in animal feedstuffs.

Ergot alkaloids are toxic and the disease has an insidious way of getting eaten.

LIFE CYCLE - Figure 11 - 88.

Ascospores infect open flowers and infect ovary directly or through the stigma. The fungus then produces lots of "honey dew" full of Sphacelia conidia which are carried flower to flower by insects.

Honey dew production ceases and the infected ovary is replaced by a fungal sclerotium that develops at the same rate as the seed.

Control?

Apple Scab - Venturia inaequalis

Occurs wherever apples are grown. Favored by cool moist conditions particularly in the spring. It is the most important disease of apples.

Early symptoms begin young leaves or sepals as light colored irregular spots. The disease then become velvet black and finally shiny black and almost circular in outline. The scab can affect leaves causing curling and defoliation and can affect fruit which is very serious because of zero tolerance. Severe disease results in low yield and no fruit.

LIFE CYCLE - Figure 11-90:

Fungus overwinters as perithecia in dead leaves on the ground. They actually develop in the winter and wet weather in spring rehydrates them to exude ascospores.

Control?

Brown Rot of Stone Fruits - Monilinia fructicola

Occurs world wide on peaches, cherries, plums, apricots and almonds.

Yield loss is due to fruit rot and destruction of flowers.

The fungus is an apothecial ascomycete. The disease starts as small brown spots on the flowers and peduncle.

The disease can cause complete loss of the flowering organs of the plant and if any fruit survives to maturity they become covered with brown spots which coalesce and form tufts of the Monilia conidia (Anamorph) which act as the summer inoculum. Finally the fruit become mummified after the rot with pseudosclerotia formed in the fruit Apothecia form in the spring from the Mummies and start the cycle over again.

DISEASE CYCLE - Figure 11-92

Control?

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