Screening of resynthesized hexaploid wheats for durable rust resistance

Wheat is one of the most important food crops, and its yield losses range from 20 to 100% due to leaf, stripe and stem rusts caused by Puccinia triticina, P. striiformis and P. graminis, respectively. New sources of resistance are strategically essential to limit the devastating effect of ever-evolving rust pathogens. In this study, we characterized 200 synthetic hexaploid wheats (SHWs) against all three rusts using rust pathotypes at seedling and adult plant stages in Queensland, Australia. We identified 57 accessions resistant to leaf rust, 77 to stripe rust and 69 accessions resistant to stem rust at the seedling stage. Ten SHWs were resistant to all three rusts, while 32 SHWs had dual resistance against leaf and stem rusts, and 28 SHWs had dual resistance to stripe and stem rust. We identified 24 SHWs carrying adult plant resistance (APR) for leaf, stripe and stem rust. The coefficient of correlation between yellow rust scores at seedling and adult plant stages were highest (r= 0.89), followed by stem rust (r= 0.77), and leaf rust (r= 0.72), which indicate the possibility of adult plant resistance in SHWs. The diagnostic kompetitive allele-specific PCR (KASP) markers for known rust resistance genes revealed that 14 SHW accessions carried Lr34, 85 carried Lr46, and 3 SHW carried Lr67, while none of the SHW carried Sr2. This study identified useful SHW lines for breeding resistance against all three types of rusts; some carried known durable resistance genes while others likely carry novel resistance loci.