APS Homepage

Poster: Biology & Disease Mgmt: Mycology


Ascospore biology of Parastagonospora nodorum under Norwegian field conditions
A. FICKE (1), B. Asalf (2), A. Ruud (3) (1) Norwegian Institute for Bioeconomic Research, Norway; (2) Norwegian Institute of Bioeconomy Research, Norway; (3) Norwegian University of Life Sciences, Norway

P. nodorum (syn. Stagonospora nodorum) is the dominant pathogen of the Norwegian leaf blotch disease complex on wheat and can cause substantial yield losses. To improve the forecasting model for leaf blotch diseases, available at our web-based pest- and disease forecasting platform (vips-landbruk.no), we studied ascospore biology of P. nodorum. Airborne ascospores were monitored with Burkard volumetric spore traps for three years in southeastern Norway. In the laboratory, we conducted wind tunnel studies to examine the effect of simulated rain and light conditions on ascospore discharge. We determined the mating types for 117 P. nodorum isolates (MAT1 and MAT2) using MAT-specific primers and inoculated wheat plants with opposite mating types to follow ascocarp maturation under field conditions. In the field, ascospore dispersal was not associated with rain events nor any specific day/night periodicity, but with daily relative humidity above 70 %. In the laboratory, over 95 % of ascospores were released during simulated rain events at 100% relative humidity, independent of light conditions. Mating type ratios of P. nodorum varied with location between 1:1 and 1:2 (M1:M2). Mature ascocarps formed 12 months after inoculation, corresponding to 551 degree-days (base 10°C) for the 2014/2015 season. We conclude that ascocarp formation can take an extended period of time and that daily humidity above 70 % is sufficient for ascospore release in the field.