Detection and evaluation of residual effects by defeated stripe rust resistance genes (Yr genes) in common wheat against virulent Puccinia striiformis f. sp. tritici isolates

Non-Peer ReviewedRace-specific stripe rust resistance genes (Yr genes) have been deployed into wheat cultivars against stripe rust caused by Puccinia striiformis f. sp. tritici Eriks. (Pst); however, the resistance has been quickly broken down only years after its introduction. Near isogenic lines (NILs) with defeated Yr genes were used in this study to evaluate partial non-race-specific resistance of the residual effect as possible durable resistance. The parental NILs with single Yr genes (Yr10, Yr26, Yr32) with Avocet background, F5 NILs with two Yr genes in the combinations of Yr26/Yr10, Yr32/Yr10 and Yr32/Yr26 and susceptible cultivar Avocet were inoculated with one of three Pst inoculums (W020, W049, T034+W052) virulent to all three Yr genes and infection type (IT), infection area (IA) and latent period (LP) were recorded. The same NILs were tested in stripe rust nurseries at Saskatoon, SK and Lethbridge, AB in 2018 and disease incidence and severity were recorded. The range of IT tended to be lower in NILs with Yr32/Yr10 and Yr32/Yr26 genes only with T034/W052. With different isolates, IA was reduced more often in the NILs with Yr32/Yr10 and Yr32/Yr26 genes than with Yr26/Yr10. The extension of LP correlated with reduction of IA. In disease nurseries, the natural Pst population appeared to be avirulent to Yr10 and Yr26 at both locations and the results were inconclusive. These results from growth chamber experiments suggest that residual effect by defeated Yr genes possibly exists in certain combinations