EPWS 310 - PLANT PATHOLOGY
Readings: Page
445-452
TODAY -
Taphrinales and Powdery Mildews
LEAF CURL DISEASES CAUSED BY TAPHRINALES
Only one genus Taphrina.
Cause hyperplasia and hypertrophy of leaves, flowers and fruit.
Important on
peach, nectarine, and plum. also on forest trees eg Oaks.
In humid areas
Eastern US and Europe.
Life cycle
Figure 11-47
Disease causes
fruit and leaf drop, the first symptoms are swelling and distortion downward
and inward. Leaves show signs of stress turning reddish and finally gray powdery
as fungus sporulates. Leaves are chlorotic and drop.
Mycelium is
dikaryotic and overseasons as ascopores on buds and fallen leaves.
Grow
intercelluarly no haustoria and cause great cell enlargement.
Control is
effected by a single or two fungicide spray(s) in late autumn or in early
spring. (Exposed ascospores).
These are in the
order Erysiphales: Very common diseases found in dry areas or during dry
periods of the year
Biotrophic
SYMPTOMS: White
to grey powdery mildew on both sides of the leaf occurring during dry weather.
Whitish mycelium can cover the whole plant and the plant eventually becomes
yellow to necrotic. Tiny Cleistothecia begin as white pin points develop into
black cleistothecia in older necrotic tissue late in the season.
Overseasons as
cleistothecia and mycelium in plant debris.
Germination of
spores is inhibited by free water and occurs at RH as low as 80%
cf. Downy
mildews.
There are only
about 6 genera of Powdery mildews which cause economic damage.
These are Erysiphe
cichoracearum - Cucurbits, Lettuce, Asteraceae
E. polygoni - beans, soybeans,
legumes, crucifers
Blumeria
graminis
- Grasses and cereals
Microsphaera - berries, oak
rhododendron
Phyllactinia - elm, maple, oak
Podosphaera - fruit trees, apples,
pears, cherry, apricot
Sphaerotheca - Rosaceae, strawberry,
berries (gooseberry)
Uncinula - Grape
These can be
identified by the structure of the cleistothecial appendages.
See Figure 11-50
Powdery
Mildew of Rose:
Occurs worldwide
and shows an example of physiologic specialization. The pathogen is Sphaerotheca
pannosa f. sp. rosae. The peach f. sp. does not infect rose and
vice versa. Leaves and buds are attacked and can cause defoliation under moist
(not wet) conditions during warm - hot weather.
Biotrophic -
intercellular growth and haustoria.
During cool
weather in fall conidiation stops and cleistothecia form.
Overseasons as
Cleistothecia and as mycelium in LIVING buds. In glasshouses overseasoning is
entirely as mycelia in buds etc.
Control -
Resistance but variable due to the existence of races in the pathogen. Further
control with fungicides benomyl, sulfur based.