Identification and characterisation of resistance to take-all fungus in wheat (HGCA Student Report No. 31)

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. Identifying plant material that would be useful for take-all control via a genetic approach has not been successful 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. 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. The effect of a low or high TAB first wheat variety on takeall 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 the hexaploid wheat varieties to take-all was evaluated in third wheat field trials. No variety was highly resistant but the variety Hereford displayed some potential partial resistance to take-all. The ability of wheat varieties to build-up take all inoculum in the soil during a first wheat crop was not related to their susceptibility to take-all root infection in the third wheat field trials. The implications of these new findings for the control of take-all via two distinct plant genetic approaches are discussed.