A Moroccan <i>Pyrenophora teres</i> f. <i>teres</i> Population Defeats <i>Rpt5</i>, the Broadly Effective Resistance on Barley Chromosome 6H

Abstract

Net form net blotch (NFNB), caused by <i>Pyrenophora teres</i> f. <i>teres</i>, is an important barley disease. The centromeric region of barley chromosome 6H has often been associated with resistance or susceptibility to NFNB, including the broadly effective dominant resistance gene <i>Rpt5</i> derived from barley line CIho 5791. We characterized a population of Moroccan <i>P. teres</i> f. <i>teres</i> isolates that had overcome <i>Rpt5</i> resistance and identified quantitative trait loci (QTL) that were effective against these isolates. Eight Moroccan <i>P. teres</i> f. <i>teres</i> isolates were phenotyped on barley lines CIho 5791 and Tifang. Six isolates were virulent on CIho 5791, and two were avirulent. A CIho 5791 × Tifang recombinant inbred line (RIL) population was phenotyped with all eight isolates and confirmed the defeat of the 6H resistance locus formerly mapped as <i>Rpt5</i> in barley line CI9819. A major QTL on chromosome 3H with the resistance allele derived from Tifang, as well as minor QTL, was identified and provided resistance against these isolates. F₂ segregation ratios supported dominant inheritance for both the 3H and 6H resistance. Furthermore, inoculation of progeny isolates derived from a cross of <i>P. teres</i> f. <i>teres</i> isolates 0-1 (virulent on Tifang/avirulent on CIho 5791) and MorSM 40-3 (avirulent on Tifang/virulent on CIho 5791) onto the RIL and F₂ populations determined that recombination between isolates can generate novel genotypes that overcome both resistance genes. Markers linked to the QTL identified in this study can be used to incorporate both resistance loci into elite barley cultivars for durable resistance.