P-073 - The Allium species reservoir of immune receptors associated with resistance to necrotrophic and hemibiotrophic plant pathogens

Onion (A. cepa) is the second most widely produced horticultural crop across the world. However, onion is very susceptible to fungal diseases caused by the necrotrophs Botrytis squamosa (Bsq) and Stemphylium vesicarium (Svs) and the hemibiotroph Fusarium oxysporum f.sp. cepae (Foc). In plants, immune receptors recognize diverse pathogen molecular factors resulting in activation of immune responses that lead to resistant phenotypes. The immune receptors in Allium species and their role in onion resistance to fungal pathogens have not been extensively studied. Therefore, we hypothesize that specific immune receptors within the Allium genetic pool could be associated with resistance to Bsq, Svs and Foc and could be exploited in onion. To locate, annotate and structurally resolve intracellular and membrane-associated receptors, we mined the available genome sequences of Allium species. Interestingly, onion shows a significant depletion of immune receptors, compared to other species. We confirmed this by performing resistance gene enrichment sequencing (RenSeq) in different Allium accessions. Next, we determined candidate receptors associated with resistance to Bsq, SvS, Foc and traced them back using RenSeq in a tri-hybrid population of onion and two closely-related Allium species. Our results indicate that despite the depletion of immune receptors in onion, closely-related Allium species represent an important immune receptor reservoir instrumental for onion breeding programs.