Background: Hexaploid wheat is one of the most important cereal crops for human nutrition. Molecular understanding of the biology of the developing grain will assist the improvement of yield and quality traits for different environments. High quality transcriptomics is a powerful method to increase this understanding.

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.

In controlled-environment experiments, ascospores of both A-group and B-group Leptosphaeria maculans were able to infect leaves of oilseed rape and produce phoma leaf spot lesions at temperatures from 5 to 208C and wetness durations from 8 to 72 h after inoculation. Lesions formed on leaves inoculated with B-group ascospores had few pycnidia and were darker, smaller and less noticable than the larger, pale grey lesions with many pycnidia produced by A-group ascospores. Lesions formed by A-group or B-group L. maculans on naturally infected winter oilseed rape experimental crops were similar to lesions produced by the two groups on inoculated plants. The greatest numbers of lesions were produced with a leaf wetness duration of 48 h and at temperatures of 15±208C for both A-group and Bgroup ascospores. As leaf wetness duration and temperature decreased below the optimal values, the number of lesions decreased. The incubation period, estimated as the time from inoculation to the appearance of the first lesions (t 1 ), or the time to the appearance of 50% of the lesions (t 50 ), of B-group was often shorter than that of A-group L. maculans. As temperature decreased below 208C, the length of the incubation period of both A-group and B-group L. maculans increased.

Ascospores of both A-group and B-group Leptosphaeria maculans germinated at temperatures from 5-20degreesC on distilled water agar or detached oilseed rape leaves. After 2 h of incubation on water agar, some A-group ascospores had germinated at 10-20degreesC and some B-group ascospores had germinated at 5-20degreesC. The percentages of both A-group and B-group ascospores that had germinated after 24 h of incubation increased with increasing temperature from 5-20'C. The observed time (Vo(50)) which elapsed from inoculation until 50% of the spores had germinated was shorter for B-group than for A-group ascospores. Germ tube length increased with increasing temperature from 5-20degreesC for both ascospore groups. Germ tubes from B-group ascospores were longer than germ tubes from A-group ascospores at all temperatures tested, but the mean diameter of germ tubes from A-group ascospores (1.8 mum) was greater than that of those from B-group ascospores (1.2 mum) at 15degreesC and 20degreesC. The average number of germ tubes produced from A-group ascospores (3.8) was greater than that from B-group ascospores (3.1) after 24 h of incubation at 20degreesC, on both water agar and leaf surfaces. Germ tubes originated predominantly From interstitial cells or terminal cells of A-group or B-group ascospores, respectively, on both water agar and leaf surfaces. Hyphae from A-group ascospores grew tortuously with extensive branching, whilst those from B-group ascospores were predominantly long and straight with little branching, whether the ascospores were produced from oilseed rape debris or from crosses between single ascospore isolates, and whether ascospores were germinating on water agar or leaf surfaces

Ascospores of both A‐group and B‐group Leptosphaeria maculans germinated at temperatures from 5 to 20°C on leaves of oilseed rape. Germination of ascospores of both groups started 2 h after inoculation and percentage germination reached its maximum about 14 h after inoculation at all temperatures. Both the percentage of A‐/B‐group ascospores that had germinated after 24 h incubation and germ tube length increased with increasing temperature from 5 to 20°C. Germ tubes from B‐group ascospores were longer than those from A‐group ascospores at all temperatures, with the greatest difference at 20°C. Hyphae from ascospores of both groups penetrated the leaves predominantly through stomata, at temperatures from 5 to 20°C. A‐group ascospores produced highly branched hyphae that grew tortuously, whereas B‐group ascospores produced long, straight hyphae. The percentage of germinated ascospores that penetrated stomata increased with increasing temperature from 5 to 20°C and was greater for A‐group than for B‐group L. maculans after 40 h incubation.