Identification and characterisation of resistance to the take-all fungus in wheat. PhD thesis, University of Exeter

Take-all disease, caused by the soil-borne fungus Gaeumannomyces graminis var. tritici, is the most devastating root disease of wheat around the world. Typical take-all symptoms show as black necrotic lesions on the roots and when severe can cause premature ripening and stunting of the wheat crop, resulting in poor grain quality and yield loss. Both cultural and chemical control methods are moderately successful at controlling take-all but plant material that would be useful for take-all control via a genetic approach has not been identified in the UK or elsewhere. The main aim of this project was to identify resistance to take-all within wheat (Triticum spp.);This study explored a new phenomenon in hexaploid wheat (Triticum aestivum) which restricts take-all inoculum build-up (TAB) in the soil during a first wheat crop and also explored tissue based resistance to take-all in hexaploid wheat and a related diploid wheat species, Triticum monococcum. Forty-nine elite wheat varieties were evaluated for their ability to build-up take-all inoculum in first wheat field trials using a soil core bioassay method, and pedigree and molecular marker analyses were carried out to investigate the genetic sources of the TAB trait. The effect of a low or high TAB first wheat variety on take-all disease and yield in a following second wheat crop was evaluated in crop rotation field trials. This work demonstrated that there are significant differences between current elite wheat varieties screened for the TAB trait and that there are probably multiple genetic sources of the trait. Take-all disease was lower and yields generally higher in a second wheat crop after a low TAB first wheat;The susceptibility of fifty elite hexaploid wheat varieties and thirty-four T. monococcum accessions to take-all was evaluated in third wheat field trials. Both T. aestivum (variety Hereford) and T. monococcum (MDR031 and MDR046) genotypes with some partial resistance to take-all were identified. A seedling pot test method as a screen for resistance was also explored but the results were found not to be closely related to the susceptibility of adult plants in field trials. The implications of these new findings for the control of take-all and further research are discussed.