Characterization of new sources and superior gene combinations for durable resistance to leaf rust in barley

Abstract

One hundred fourteen barley lines were screened with diverse pathotypes (pts) of Puccinia hordei in the greenhouse (GH) and field to characterize resistance. The GH tests revealed the presence of all stage resistance (ASR) genes Rph1, Rph2, Rph3, Rph12 and Rph19 either individually or in combination, whereas field tests revealed the presence of adult plant resistance (APR) in 74.5% of the test lines. Molecular markers linked to known genes demonstrated presence of Rph15 (3 lines), Rph20 (5 lines), Rph23 (8 lines), Rph24 (19 lines), and the combinations Rph20+Rph23 or Rph20+Rph24 or Rph23+Rph24 (8 lines). The remaining 49 resistant lines probably carry new uncharacterized ASR and/or APR genes. Genome wide association studies (GWAS) detected a total of 15 QTL that were strongly associated with markers. Among them, QTL MTA8_R2 (chromosome 7H) has the largest effect in controlling leaf rust. Temperature and interaction studies revealed that the expression of Rph1.a, Rph2.b, Rph4.d and Rph10.o altered with temperature, whereas the expression of genes Rph3.c, Rph5.e, Rph6.f, Rph12 (9.z), Rph13.x and Rph15.ad was concluded to be non-sensitive to temperature. Amongst a selection of lines carrying Rph20 (Flagship), Rph23 (Yerong) and Rph24 (ND24260), only seedlings of Flagship showed improved resistance with lower temperatures against pt 200 P-, whereas seedlings of Yerong and ND24260 showed high IT at all three temperatures with pt 5457 P+. When RphASR genes were combined with the APR gene Rph20, combinations Rph2.b+Rph20, Rph4.d+Rph20, Rph5.e+Rph20, Rph9.i+Rph20 and Rph15.ad+Rph20 showed an enhanced level of resistance. Seedlings carrying the combination Rph5.e+Rph20 remained resistant even when challenged with the Rph5.e-virulent pt 220 P+ + Rph13, suggesting a residual or ghost effect of Rph5.e when present in combination with Rph20. This study was the first to demonstrate that several ASR Rph genes interact with the APR gene Rph20 in an additive manner.