Uniting genetics and chemistry to reduce the risk of take-all disease in commercial second wheats
Thesis or dissertation
University of Exeter
We wish to place a 5 year embargo on this thesis.
Reason for embargo
We wish to place an extended embargo on the PhD thesis of the student Joseph Moughan and withhold consent for this thesis to be publicly available on ORE or to the British Library until 1st October 2022. The reasons are as follows: This PhD project was 100% funded by industry. The thesis contains commercially sensitive results, i.e. (a) the mapping of quantitative trait loci to a new wheat root trait that will be used in commercial breeding programmes, (b) information on the sensitivity/insensitivity of soil dwelling fungi to a commercial fungicide, and (c) a new approach to control take all diseases. These results will be used commercially in the future and therefore the project sponsor wishes to keep this substantial amount of new information from competing companies.
Gaeumannomyces tritici is a soil-borne, highly destructive, wheat root pathogen, causing take-all disease. Some modern, elite, winter wheat cultivars possess a genetic trait promoting low take-all inoculum build-up (LowTAB). This leads to reduced disease if wheat is grown in the same field the next year. This PhD aimed to test if genetics (LowTAB) and chemistry will individually or synergistically influence take-all fungal inoculum build-up in first wheats as methods to control second wheat take-all disease. The underlying mechanism, epidemiology, agronomy and genetics of the TAB (take-all build-up) trait in eight first wheat field trials was investigated. This identified two minor QTLs conferring the LowTAB trait, in a doubled haploid mapping population. This PhD also confirms the highly complex cultivar-year-field interactions that underpin this trait. Root phenotyping experiments in the field and laboratory highlight that the TAB trait is not likely to be the result of root system architecture variation. Future field trials are planned to confirm the QTLs identified and to test for links between TAB and root-soil-microbial interactions. The effect of foliar applied chemistry (fungicide: Amistar, active ingredient: azoxystrobin and plant growth regulator: Moddus, a.i. trinexapac-ethyl) combined with genetics (TAB) on first wheat take-all inoculum build-up and second wheat disease was investigated. To complement this, laboratory screens were performed checking for common target site mutations to the azoxystrobin fungicide, in new and historic G. tritici isolates. For the first time, legacy effects of first wheat foliar chemistry on second wheat disease were identified, however no synergy with genetics were found. Early first wheat Amistar sprays reduced second wheat take-all disease, whilst later sprays and plant growth regulator, Moddus; had no effect. However, first wheat inoculum reduction by Amistar, could not be directly linked to the second wheat disease outbreaks observed. No evidence of fungicide resistance was found in 40 UK isolates, thus the varied efficacy of Amistar is linked to soil dose rate at the different application times. The collective PhD findings of the effect of first wheat chemistry and genetics make a significant contribution to the control of take-all disease in commercial second wheat crops.
Full financial support from Syngenta UK Ltd.
PhD in Biological Sciences