EPWS 310 - PLANT PATHOLOGY
Readings: Page 445-452
TODAY - Taphrinales and Powdery Mildews
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
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.