EPWS 310 - PLANT PATHOLOGY
LECTURE 12: ASCOMYCETES AND DEUTEROMYCETES
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 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.
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.
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.