Effects of temperature on maturation of pseudothecia ofLeptosphaeria maculansandL. biglobosaon oilseed rape stem debris

Abstract

Effects of temperature on maturation of pseudothecia ofLeptosphaeria maculansandL. biglobosa, closely related species which coexist on UK oilseed rape, were investigated. Stages in pseudothecial maturation on naturally infected oilseed rape debris were examined, both in controlled environments (5, 10, 15 or 20°C) under continuous wetness and in natural conditions (debris exposed in September and December 2000, and July, September and November 2002). Pseudothecia sampled weekly were assigned to maturation classes A (asci undifferentiated), B (asci differentiated), C (ascospores differentiated) or D (ascospores mature). Progress in pseudothecial maturation (assessed by time until 50% of pseudothecia reached each class) was similar forL. maculansandL. biglobosaat 15–20°C, butL. biglobosamatured more slowly at < 10°C. Maturation time decreased almost linearly with temperature from 5 to 20°C under continuous wetness but was longer in natural conditions, especially when periods of dry weather occurred. Differences in pseudothecial maturation are likely to contribute to epidemiological differences betweenL. maculansandL. biglobosa, which may explain their coexistence. It is appropriate to use the degree‐day approximation to assess pseudothecial maturation at temperatures between 5 and 20°C, providing debris is wet.