Understanding the expression and interaction of Rph genes conferring seedling and adult plant resistance to Puccinia hordei in barley

Abstract

Leaf rust caused by Puccinia hordei is a major disease of barley and is best managed by deploying effective resistance genes. The effect of post-inoculation temperature [18 ± 2°C (low), 22 ± 2°C (mid), or 26 ± 2°C (high)] on the expression of a selection of known all stage resistance (ASR) Rph genes and their interaction in combination with the adult plant resistance (APR) gene Rph20 were investigated in barley. Rph1.a and Rph2.b expressed best at higher temperatures whereas Rph4.d lost its effectiveness at higher temperatures when tested with pathotype (pt) 200 P− (avirulent on these genes). The expression of the genes Rph3.c, Rph5.e, Rph6.f, Rph12 (9.z), Rph13.x and Rph15.ad was not affected by post-inoculation temperature. The interaction between Rph14.ab and pt 5457 P+ gave the lowest infection type at low post-inoculation temperature. Among a selection of lines carrying Rph20 ('Flagship'), Rph23 ('Yerong') and Rph24 ('ND24260ʹ), higher levels of resistance were observed in seedlings of 'Flagship' (Rph20) at lower temperatures, while seedlings of 'Yerong' (Rph23) and 'ND24260ʹ (Rph24) showed high infection types at all three temperatures with pt 5457 P+. When RphASR genes were combined with the APR gene Rph20 an enhanced level of seedling resistance was observed in the six combinations: Rph1.a+Rph20, Rph2.b+Rph20, Rph4.d+Rph20, Rph9.i+Rph20, Rph5.e+Rph20 and Rph15.ad+Rph20. Seedlings carrying the Rph5.e +Rph20 combination remained resistant when challenged with the Rph5.e-virulent pt 220 P+ + Rph13, suggesting a residual effect of Rph5.e when present in combination with Rph20. This is the first study to demonstrate that several ASR Rph genes interact with the APR gene Rph20 in an additive manner, emphasizing the importance of deploying genes in combination rather than individually to achieve durable resistance.

The genetic basis and interaction of genes conferring resistance to Puccinia hordei in an ICARDA barley breeding line GID 5779743

“…Mecknes Maroc ( Elmansour et al, 2017 ). Very recently, Singh et al (2021) reported on the interaction of an APR ( Rph20 ) and an ASR ( Rph5.e ) gene conferring resistance to P. hordei virulent pathotype. In soybean, the resistance of accession JS 95-60 to the fungus Colletotrichum truncatum was also regulated by the interactions of two major genes in complementary fashion ( Nataraj et al, 2020 ).…”

“…Interestingly, combinations of various “defeated” genes providing residual effects have been reported in multiple crops against different pathogens ( Nass et al, 1981 ; Royer et al, 1984 ; Brodny et al, 1986 ; Li et al, 1999 ). The interaction of an APR and an ASR gene conferring resistance to P. hordei virulent pathotype has also been reported ( Singh et al, 2021 ). When being singly deployed, both the ASR gene Rph5.e and the APR gene Rph20 are ineffective against the pathotype 220 P+ +Rph13 at the seedling stages.…”

Overview of Identified Genomic Regions Associated with Various Agronomic and Physiological Traits in Barley under Abiotic Stresses

“…It has been reported that barley is the fourth largest global grain crop, after wheat, rice, and corn. Barley seeds have moderate amounts of protein, phosphorus, and calcium, as well as small amounts of B vitamins [7]. Furthermore, since the carbohydrate content in barley seeds is high, they are commonly used in breads, soups, stews, and other health products [8].…”