EPWS 310 - PLANT PATHOLOGY

LECTURE 12: ASCOMYCETES AND DEUTEROMYCETES

Alternaria Diseases

Mycosphaerella Diseases

Septoria Diseases

Readings: Page 452-472

TODAY - Foliar diseases caused by Alternaria, Mycosphaerella, Septoria, Cochliobolus and Pyrenophora.

These fungi cause many different diseases of the leaves, fruit, stems, flowers and sometime roots.

They are necrotrophs, facultative saprophytes and parasites. They are VERY common and the diseases range from mild (no control needed) to very serious.

ALTERNARIA DISEASES

Alternaria is the anamorph very few species have been shown to have a teleomorph.

Leaf spots and blights the most serious of which are early blight of potato and tomato. Leaf spot of bean and blight of carrot.

The diseases are characterized by dark brown to black spots often with concentric rings of sporulation.

The older more senescent leaves and stems are attacked first often resulting in leaf drop from the bottom up. Target like spots can occur on the stem and may be sunken. These may result in the death of the whole stem and cause blight like syndrome.

The conidia are very characteristic and can be identified directly on the diseases plant tissue !!! However Alternaria is a very common saprophyte therefore you MUST do Koch's postulates.

Many species produce toxins both host specific and non-specific.

LIFE CYCLE Fig 11-53

Control, if warranted by resistance, clean seed, as always sanitation, and fungicides using spray advisories. Favored by high humidity and warm temperatures.

MYCOSPHAERELLA DISEASES

An Ascomycete in the Dothidiales with anamorphs of various types e.g. Cercospora, Septoria, Ascochyta, Ramularia, and Didymella. (All ANAMORPHS).

These diseases are all leaf spots very serious on banana and peas and other vegetables.

The diseases are actually leaf spots generally starting out chlorotic spots with sporulation of the conidia through the season then formation of spermatia and perithecia later in the season. Infection by conidia and ascospores causes the same disease.

Generally leaf spots with some damage to fruit as shown for sigatoka disease of banana.

LIFE CYCLE - Fig 11-57

Overseasons as perithecia or continues to infect host all year in tropical climates.

Particularly with perennial plants and in areas with 12 month growing seasons.

CONTROL - Sanitation, fungicides on regular schedule often year round mineral oils are used but may have phytotoxic effects. May be needed as often as every 2 weeks but in some areas less frequent application will work

Some resistance but not fully effective.

SEPTORIA DISEASES

These are caused be the anamorph Septoria and can be very serious on cereal e.g. wheat and on vegetables under cool to warm temperatures and high humidity.

These are fungi that form pycnidia with teleomorphs known but not found in nature very often.

LIFE CYCLE - Fig 11-59

Overseasons as pycnidia in plant debris in and on soil.

Control Sanitation, disease free seed, resistance and rotation and fungicides.

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