The genetics of crown rot resistance in bread (Triticum aestivum L.) and durum (T. durum L.) wheats

[Truncated abstract] Crown rot (CR), caused by various Fusarium species, is a chronic wheat disease in Australia. In addition to yield losses, CR infected plants also accumulate mycotoxins which can be harmful to both human and animal if present in foods or feeds. Growing resistant wheat varieties has long been recognised as the most effective way to minimize CR but varieties with high levels of resistance are not yet available. High quality sources of resistance are rare and resistances of a few genotypes with partial resistance all seem to be controlled by inconsistent QTL with only small effects. Our capacity in breeding could be dramatically enhanced if a few different sources with high levels of resistance were available. Characterizing one of the novel sources of resistance, ‘CSCR6’ which was one of the most resistant genotypes from a screening of some 2,400 wheat genotypes, was the first objective of this project. A population derived from a cross of ‘Lang’/‘CSCR6’ was analysed using two Fusarium isolates belonging to two different species, one F. pseudograminearum and the other F. graminearum. The two isolates detected several QTL with the same chromosomal locations and comparable magnitudes, indicating that CR resistance may not be fungal species-specific. A major QTL on 3BL was found to be responsible for up to 48.8% of the phenotypic variance. The effects of this major QTL were further validated in four additional populations and the presence of this single QTL reduced CR severity by up to 42.1%. The fact that significant effects of this 3BL QTL were detected across all trials with different genetic backgrounds and with isolates belonging to two different Fusarium species make it an ideal target for breeding.