Factors affecting development of pseudothecia produced by <i>Venturia effusa</i> in vitro

Abstract Pecan scab, caused by Venturia effusa , is the most destructive disease of pecan in the south‐eastern United States. The fungus was assumed to perpetuate solely through asexually produced conidia. Yet the identification of heterothallic mating type idiomorphs has led to successful crosses producing pseudothecia in vitro. To investigate factors influencing the development of pseudothecia, three isolates of each mating type ( MAT1‐1 × MAT1‐2 ) were crossed pairwise on oatmeal agar. Pseudothecial production and maturation were assessed at 4, 8, 12, 16 and 22°C, with incubation periods of 2, 3 or 4 months, either with or without light (0 or 12 h photoperiod) during maturation. There were significant effects of temperature, month and cross on the production of pseudothecia. Similar numbers of pseudothecia were produced at 4, 8, 12 and 16°C (1.8–2.3 pseudothecia), but significantly fewer at 22°C (0.1 pseudothecia). Pseudothecia remained immature at 22°C suggesting a cold period is required for ascospore maturation. The isolate and mating type cross affected the number of pseudothecia, with both MAT1‐1 and MAT1‐2 contributing to the number produced, which interacted with time. MAT1‐1 had the greatest effect on the number of pseudothecia produced, but this was modulated by MAT2‐2 . At the highest temperature there were no differences among mating type crosses. Light had no effect on maturation of pseudothecia in this study. The results indicate the likely temperatures and durations required to produce pseudothecia in the field; ascospores may play a role as primary inoculum in the disease cycle of pecan scab.