Genetic analysis of net form net blotch resistance in barley lines CIho 5791 and Tifang against a global collection of P. teres f. teres isolates

A CIho 5791 × Tifang recombinant inbred mapping population was developed and used to identify major dominant resistance genes on barley chromosomes 6H and 3H in CI5791 and on 3H in Tifang. The barley line CIho 5791 confers high levels of resistance to Pyrenophora teres f. teres, causal agent of net form net blotch (NFNB), with few documented isolates overcoming this resistance. Tifang barley also harbors resistance to P. teres f. teres which was previously shown to localize to barley chromosome 3H. A CIho 5791 × Tifang F₆ recombinant inbred line (RIL) population was developed using single seed descent. The Illumina iSelect SNP platform was used to identify 2562 single nucleotide polymorphism (SNP) markers across the barley genome, resulting in seven linkage maps, one for each barley chromosome. The CIho 5791 × Tifang RIL population was evaluated for NFNB resistance using nine P. teres f. teres isolates collected globally. Tifang was resistant to four of the isolates tested whereas CIho 5791 was highly resistant to all nine isolates. QTL analysis indicated that the CIho 5791 resistance mapped to chromosome 6H whereas the Tifang resistance mapped to chromosome 3H. Additionally, CIho 5791 also harbored resistance to two Japanese isolates that mapped to a 3H region similar to that of Tifang. SNP markers and RILs harboring both 3H and 6H resistance will be useful in resistance breeding against NFNB.

Evaluation of a barley core collection for spot form net blotch reaction reveals distinct genotype-specific pathogen virulence and host susceptibility

Spot form net blotch (SFNB) caused by Pyrenophora teres f. maculata is a major foliar disease of barley (Hordeum vulgare) worldwide. SFNB epidemics have recently been observed in major barley producing countries, suggesting that the local barley cultivars are not resistant and that virulence of the local pathogen populations may have changed. Here we attempt to identify sources of resistance effective against four diverse isolates of P. teres f. maculata collected from around the world. A total of 2,062 world barley core collection accessions were phenotyped using isolates of the pathogen collected in the United States (FGO), Australia (SG1), New Zealand (NZKF2), and Denmark (DEN 2.6). Isolate-specific susceptibility was identified in several of the barley accessions tested, indicating variability in both pathogen virulence and host resistance/susceptibility. Collectively, only 15 barley accessions were resistant across all isolates tested. These resistant accessions will be used to generate mapping populations and for germplasm development. Future research will involve the characterization of host resistance, pathogen virulence, and the host-pathogen interaction associated with SFNB of barley.

Resistance to stem rust race TTKSK maps to the rpg4/Rpg5 complex of chromosome 5H of barley

Race TTKSK (Ug99) of the wheat stem rust pathogen (Puccinia graminis f. sp. tritici) is a serious threat to both wheat and barley production worldwide because of its wide virulence on many cultivars and rapid spread from eastern Africa. Line Q21861 is one of the most resistant barleys known to this race. To elucidate the genetics of resistance in this line, we evaluated the Q21861/SM89010 (Q/SM) doubled-haploid population for reaction to race TTKSK at the seedling stage. Segregation for resistance:susceptibility in Q/SM doubled-haploid lines fit a 1:1 ratio (58:71 with chi2=1.31 and P=0.25), indicating that a single gene in Q21861 confers resistance to race TTKSK. In previous studies, a recessive gene (rpg4) and a partially dominant gene (Rpg5) were reported to control resistance to P. graminis f. sp. tritici race QCCJ and P. graminis f. sp. secalis isolate 92-MN-90, respectively, in Q21861. These resistance genes co-segregate with each other in the Q/SM population and were mapped to the long arm of chromosome 5H. Resistance to race TTKSK also co-segregated with resistance to both rusts, indicating that the gene conferring resistance to race TTKSK also lies at the rpg4/Rpg5 locus. This result was confirmed through the molecular analysis of recombinants previously used to characterize loci conferring resistance to race QCCJ and isolate 92-MN-90. The 70-kb region contains Rpg5 (a nucleotide-binding site leucine-rich repeat serine/threonine-protein kinase gene), rpg4 (an actin depolymerizing factor-like gene), and two other genes of unidentified function. Research is underway to resolve which of the genes are required for conferring resistance to race TTKSK. Regardless, the simple inheritance should make Q21861 a valuable source of TTKSK resistance in barley breeding programs.