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

Abstract

Effects of temperature on maturation of pseudothecia of Leptosphaeria maculans and L. 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 for L. maculans and L. biglobosa at 15–20°C, but L. biglobosa matured 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 between L. maculans and L. 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.

Quantitative PCR analysis of abundance of airborne propagules of Leptosphaeria species in air samples from different regions of Poland

“…are released from pseudothecia produced on winter oilseed rape stubble of the previous season's crop (Toscano-Underwood et al 2003). Spores germinate on host leaf surfaces and penetrate through stomata, producing phoma leaf spot lesions in the autumn ).…”

Analyses of air samples for ascospores ofLeptosphaeria maculans andL.biglobosa by light microscopy and molecular techniques

“…All parts of the susceptible oilseed rape host can be colonized by these pathogens, including the tap root, stem base, upper stem parts, leaves, cotyledons, and seeds (Paul and Rawlinson 1992). In Europe, the first disease symptoms on winter oilseed rape appear in autumn, when cotyledons and leaves are inoculated naturally with airborne ascospores (sexual spores), which germinate to penetrate and cause phoma leaf spot lesions (West et al 1999;Toscano-Underwood et al 2003). Thereafter, mycelia of the pathogens colonise host tissues biotrophically, through endophytic growth within the petiole, to reach the stem where stem lesions and damaging basal stem cankers are produced (Hammond et al 1985).…”

Monitoring blackleg (Leptosphaeria spp.) ascospore release timing and quantity enables optimal fungicide application to improved oilseed rape yield and seed quality

“…If stubble is left standing after harvest, the stem base has a higher water content than upper parts of the stem (Fitt et al 2006b). As moisture is required for pseudothecial maturation (Salam et al 2003;Toscano-Underwood et al 2003), therefore, ascospore release of the pathogen that has colonised the stem base will be earlier than that of the pathogen that has colonised the upper stem (Fitt et al 2006b). On the other way, our recent experiments using oilseed rape varieties with Rlm7 resistance genes have shown their cultivation may contribute to the increase of the population of L. biglobosa, due to great efficiency in the control of disease symptoms caused by L. maculans.…”