david.gilbert@jic.ac.uk and sanu.arora@jic.ac.uk

Eyespot, caused by the fungal pathogens Oculimacula yallundae and Oculimacula acuformis, is a historically important disease of wheat and other cereals. To date, limited resistance loci have been deployed in wheat, with breeding largely focusing upon the usage of a single R gene, Pch1. However, whilst Pch1 has shown an enduring efficacy against both eyespot causative pathogens, dependency upon a single or handful of resistance sources is a strategy that has proven persistently unwise.

With numerous examples of R gene breakdown often associated with single gene deployment. Perhaps worryingly, efforts to identify further sources of resistance amongst wheat landraces and cultivars has failed to yield any new major effect loci. Indeed, whilst Pch2 (and a separate QTL, QPch.jic-5A) were identified in French wheat cultivar Capelle deprez, both Pch1 and Pch3 were derived or detected in wheat wild relatives Aegilops ventricosa and Dasypyrum villosum respectively.

In our research, through a collaborative project with an industrial partner, RAGT, we have focused on identifying the causative sources of resistance to O. yallundae infection that has been reported in Ae. tauschii. Utilising historical and newly generated data combined with k-mer based association genetics we have uncovered an NLR gene on chromosome 1D that provides protection against O. yallundae in addition to a new QTL detected on chromosome 3D.

We have provisionally designated it as Pch4 and have shown that resistance segregates in an additive dominant manner and conveys the same level of resistance when transferred into wheat. Pch4 provides an equivalent resistance in wheat as Pch1 and will therefore be useful for introducing into breeding programs. Excitingly, we show that whilst this gene is the dominant source of resistance in Ae. tauschii, there are other unknown sources available.

To our knowledge this is the first example of an R gene cloned from Ae. tauschii that conveys protection against a soil borne pathogen, and therefore opens new avenues for future research.