|BELACHEW, ASALF - Norwegian University Of Life Sciences|
|STENSVAND, ARNE - Norwegian Institute For Food Research|
|GADOURY, DAVID - Cornell University|
|SEEM, ROBERT - Cornell University|
|PERES, NATALIA - University Of Florida|
|TRONSMO, A - Norwegian University Of Life Sciences|
Submitted to: American Phytopathological Society Abstracts
Publication Type: Abstract Only
Publication Acceptance Date: 3/15/2012
Publication Date: 5/1/2012
Citation: Belachew, A., Stensvand, A., Gadoury, D., Seem, R., Cadle Davidson, L.E., Peres, N., Tronsmo, A.M. 2012. Temperature functions as a repressor of ascocarp formation in strawberry powdery mildew Podoshpaera aphanis. American Phytopathological Society Abstracts. Phytopathology 102:S.
Technical Abstract: The asexual stage of Podosphaera aphanis occurs wherever strawberries are grown, but cleistothecia are reportedly rare in subtropical climates where the disease is nonetheless severe. We confirmed that the pathogen is heterothallic, and that both mating types are present in Florida, USA. Pairing compatible isolates under controlled temperatures indicated that ascocarp formation was suppressed above 15C. Abundant mycelial growth occurred at both 15C and 25C, thus lack of ascocarp production was not caused by lack of contact between mating types within the mildew colony. Furthermore, subsequent investigations of diurnal temperature fluctuation indicated that nightly exposure to cold (less than 13C) for 1 to 4 hours was sufficient to stimulate ascocarp formation in the presence of higher (25C) daytime temperatures. Additional episodes of overnight cold resulted in more prolific ascocarp production despite higher daytime temperatures. Our results suggest that cleistothecia of P.aphanis may be suppressed in subtropical areas by high temperature during the warmest periods of the year, but may appear if strawberry plants in annual production systems are exposed to cooler temperatures late in the production cycle. The foregoing also suggests that ascocarp formation might be minimized or prevented in high tunnel production systems by avoiding temperatures below 13C. Geographical distribution of mating types as confirmed by specific markers will also be reported.