Disease and Stress Biology Department, John Innes Centre, Norwich Research Park, Colney Lane, Norwich, NR4 7UH, UNITED KINGDOM
In Europe, the need to understand and use host plant resistance to septoria tritici blotch (STB) has assumed new urgency with the widespread development of resistance to QoI (strobilurin and related) fungicides in the STB pathogen, Mycosphaerella graminicola. We have investigated factors that contribute to reducing STB levels among wheat cultivars in field conditions, including resistance to specific isolates of M. graminicola and aspects of plant development and morphology that contribute to disease escape. This has allowed the identification of cultivars which are useful sources of isolate-non-specific, foliar resistance to STB for wheat breeding.
A total of 226 wheat genotypes were studied, including cultivars grown in the UK and other lines relevant to UK breeding programmes, including progenitors of current cultivars. Eleven field trials were carried out at eight sites over three years, in which STB and escape factors were scored. All 226 lines were screened with single isolates to identify the presence of specific resistance genes using the detached leaf technique (Arraiano et al. 2001b). A sub-set of 98 lines were scored with 121 microsatellite markers covering all 21 chromosomes.
At least two specific resistance genes were associated with significant reduction of STB in the set of wheat genotypes. One of these was the most important predictor of resistance other than height to flag leaf and heading date. The development of a model which combines escape factors (heading date, plant height and leaf spacing) with specific resistances that are correlated with disease levels has enabled us to detect cultivars with greater resistance to STB than the model predicts. These are likely to be new sources of STB resistance for wheat breeding programmes in the UK and elsewhere. Other regions of the genome that may contain hitherto unknown resistance genes were identified by linkage to microsatellite markers in an association genetic analysis.
This research is providing breeders with knowledge about the potential value of genes for resistance to STB and about previously unidentified sources of resistance within the pool of wheat germplasm adapted to UK conditions. This is expected to lead to improved selection of wheat varieties with resistance to STB and in due course, to a sustained, gradual improvement in the resistance of European wheat varieties to STB and thus to reduced need for fungicides to control this disease.
Acknowledgements: This research was done in collaboration with Advanta Seeds UK, Cebeco Seed Innovations, Elsoms Seeds, Nickerson, SW Seed and Syngenta Seeds through the Sustainable Arable LINK Programme.
Arraiano LS, Brading PA, Brown JKM, 2001. A detached seedling leaf technique to study resistance to Mycosphaerella graminicola (anamorph Septoria tritici) in wheat. Plant Pathology 50: 339-346.