Rph22: mapping of a novel leaf rust resistance gene introgressed from the non-host Hordeum bulbosum L. into cultivated barley (Hordeum vulgare L.)

Abstract

A resistance gene (Rph22) to barley leaf rust caused by Puccinia hordei was introgressed from the non-host species Hordeum bulbosum into cultivated barley. The H. bulbosum introgression in line '182Q20' was located to chromosome 2HL using genomic in situ hybridisation (GISH). Using molecular markers it was shown to cover approximately 20 % of the genetic length of the chromosome. The introgression confers a very high level of resistance to P. hordei at the seedling stage that is not based on a hypersensitive reaction. The presence of the resistance gene increased the latency period of the leaf rust fungus and strongly reduced the infection frequency relative to the genetic background cultivar 'Golden Promise'. An F2 population of 550 individuals was developed and used to create a genetic map of the introgressed region and to determine the map position of the underlying resistance gene(s). The resistance locus, designated Rph22, was located to the distal portion of the introgression, co-segregating with markers H35_26334 and H35_45139. Flanking markers will be used to reduce the linkage drag, including gene(s) responsible for a yield penalty, around the resistance locus and to transfer the gene into elite barley germplasm. This genetic location is also known to harbour a QTL (Rphq2) for non-hypersensitive leaf rust resistance in the barley cultivar 'Vada'. Comparison of the 'Vada' and H. bulbosum resistances at this locus may lead to a better understanding of the possible association between host and non-host resistance mechanisms.

Marker assisted separation of resistance genes Rph22 and Rym16 Hb from an associated yield penalty in a barley: Hordeum bulbosum introgression line

“…Because of the large effect on latency period and infection frequency of Rph22, the presence of this gene can also be readily detected at the seedling stage (Pickering et al 2004a). Molecular mapping of Rph22 has revealed a small overlapping genetic interval and the same phenotypic mechanism as Rphq2 (Johnston et al 2013), the largest effect and most stable QTL from 'Vada' (Marcel et al 2007). It seems likely that Rph22 and Rphq2 are paralogs of the same ancestral gene or members of a gene cluster.…”

“…Hordeum bulbosum L. is a member of the secondary gene pool of cultivated barley (Hordeum vulgare L.) and has been used mostly in barley improvement as a means to produce doubled haploids through chromosome elimination (Kasha and Kao 1970). In addition, H. bulbosum is considered a non-host to many pathogens which are virulent upon barley, and several resistance genes have been successfully introgressed from H. bulbosum into cultivated barley (Fetch et al 2009;Johnston et al 2013;Pickering et al 1995Pickering et al , 1998Pickering et al , 2000Pickering et al , 2006Ruge-Wehling et al 2006;Ruge et al 2003;Scholz et al 2009;Shtaya et al 2007;Toubia-Rahme et al 2003;Walther et al 2000;Xu and Kasha 1992). The development of crops which are resistant to diseases is a major goal of plant breeding in almost all commercial crop species.…”

“…Rph22 is likely to be conferred by a single dominant gene located on the distal end of chromosome 2HL (Johnston et al 2013). The presence of this single locus results in an increased latency period and reduced infection frequency that is superior to the degree of resistance found in the cultivar 'Vada', which is conditioned by at least six separate QTL (Qi et al 1998).…”

“…Partial resistance genes are also known as APR genes as their effect on extending fungal latency period increases over the course of plant development (Parlevliet 1975). The introgression line '182Q20', derived from the backcross of diploid barley cultivar 'Golden Promise', to a partially fertile triploid interspecific hybrid between 'Golden Promise' and the tetraploid H. bulbosum genotype A17-1 (Johnston et al 2013) was first identified in the field because of its 'slow rusting' response to natural infections of barley leaf rust. This line was subsequently shown using genomic in situ hybridization (GISH) and molecular markers to possess a single introgression from H. bulbosum which covers approximately 6 % of the physical length (IBSC physical map, 2012) and 24 % of the genetic length (POPSEQ map, Mascher et al 2013) of chromosome 2H (N. Wendler, pers.…”

The Effect of Homoeologous Meiotic Pairing in Tetraploid <b><i>Hordeum bulbosum</i></b> L. × <b><i>H. vulgare</i></b> L. Hybrids on Alien Introgressions in Offspring

“…to leaf rust [Pickering et al, 1998[Pickering et al, , 2000Walther et al, 2000;Shtaya et al, 2007;Johnston et al, 2013], stem rust [Fetch et al, 2009], powdery mildew [Jones and Pickering, 1978;Xu and Snape, 1989;Szigat and Szigat, 1991;Xu and Kasha, 1992;Pickering et al, 1995;Michel, 1996;Shtaya et al, 2007], Rhynchosporium secalis [Pickering et al, 2006b], Septoria speckled leaf blotch [Toubia-Rahme et al, 2003], and also to barley mild mosaic virus and barley yellow mosaic virus [Szigat and Szigat, 1991;Ruge et al, 2003;Ruge-Wehling et al, 2006]. Recently, Scholz et al [2009] succeeded in transferring a gene for resistance to barley yellow dwarf virus into H. vulgare ( Hv ).…”