GENETICS OF SEEDLING AND ADULT-PLANT RESISTANCE TO NET BLOTCH (PYRENOPHORA-TERES F TERES) AND SPOT BLOTCH (COCHLIOBOLUS-SATIVUS) IN BARLEY

Net blotch (caused by Pyrenophora teres f. teres) and spot blotch (Coc hliobolus sativus) are important foliar diseases of barley in the midw estern region of the USA. To determine the number and chromosomal loca tion of Mendelian and quantitative trait loci (QTL) controlling resist ance to these diseases, a doubled haploid population ('Steptoe'/'Morex ') was evaluated to the pathogens at the seedling stage in the greenho use and at the adult plant stage in the field. Alleles at two or three unlinked loci were found to confer resistance to the net blotch patho gen at the seedling stage depending on how progeny exhibiting an inter mediate infection response were classified. This result was corroborat ed in the quantitative analysis of the raw infection response data as 2 major QTL were identified on chromosomes 4 and 6M. A third QTL was a lso identified on chromosome 6P. Seven QTL were identified for net blo tch resistance at the adult plant stage and mapped to chromosomes 1P, 2P, 3P, 3M, 4, 6P, and 7P. The 7 QTL collectively accounted for 67.6% of the phenotypic variance under a multiple QTL model. Resistance to t he spot blotch pathogen was conferred by a single gene at the seedling stage. This gene was mapped to the distal region of chromosome 1P on the basis of both qualitative and quantitative data analyses. Two QTL were identified for spot blotch resistance at the adult plant stage: t he largest QTL effect mapped to chromosome 5P and the other mapped to chromosome 1P near the seedling resistance locus. Together, the 2 QTL explained 70.1% of the phenotypic variance under a multiple QTL model. On the basis of the chromosomal locations of resistance alleles detec ted in this study, it should be feasible to combine high levels of res istance to both P. teres f. teres and C. sativus in barley cultivars.