Blackwell Publishing Journal Backfiles 1879-2005
Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
Earlier studies have shown that primary infections of winter wheat crops by septoria tritici blotch are initiated in autumn by air-borne ascospores of the teleomorph stage, Mycosphaerella graminicola, which originate from sources outside the crop. Subsequent disease development within the crop, and damage to the upper leaves in summer, were commonly ascribed to the anamorph stage, Septoria tritici, which first arises from primary, ascosporic lesions and develops to give rise to splash-borne pycnidiospores produced in pycnidia. Trapping studies, using a Burkard volumetric trap sited adjacent to field trials of winter wheat, showed that ascospores are released from pseudothecia throughout the year; peak release is not restricted to the autumn and early winter when the primary infections occur. As M. graminicola ascospores can be confused with those of other species, their authenticity was established by incubating ascospores on trap tapes for 24–48 h before counting. Examination of wheat plants cv. Riband, removed from unsprayed crops just prior to harvest and exposed to external weather conditions over the winter in 1995 and 1996, showed that pseudothecia mature on residues of the upper leaf layers between August and March. However, peak development occurred in December/January, when there was a corresponding decline in pycnidial formation. On regenerated wheat in set-aside (left uncultivated) fields, sources of pseudothecia of M. graminicola were exhausted by February of the following year. Natural development of the teleomorph stage was monitored in an unsprayed crop of winter wheat cv. Riband during the 1996–97 season, and was present on leaf 8 at growth stage 32 (24 April) and on leaf 3 at growth stage 85 (8 July), then a week later, on both leaf 2 and the flag leaf. The temporal development of M. graminicola asexual and sexual phases was also studied in inoculation experiments under external weather conditions on pot-grown seedlings of winter wheat cv. Longbow, using inoculum from two single-ascospore cultures.
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