Determining quantitative resistance of barley cultivars at the seedling stage to net blotch caused by Pyrenophora teres

Abstract

Four barley (Hordeum vulgare L.) cultivars, Heartland, Harrington, Johnston, and Kasota, were compared a: the seedling stage for reactions to the net and spot forms of net blotch caused by Pyrenophora teres f. teres and P. teres f. maculata, respectively. Effects of leaf wetness period, leaf position, and inoculum concentration on lesion development were investigated. The linear relationship between inoculum concentration and diseased leaf area was used to estimate inoculum concentrations causing 50% diseased leaf area (ED50) on leaf 2 (the second seedling leaf) and causing 15% diseased leaf area (ED15) on leaf 3 (third seedling leaf). Resistance of cultivars was compared on the basis of ED50 and ED15. The linear relationship of diseased leaf area with time was used to estimate the rate of lesion spread and to compare resistance. Lack of a significant linear relationship over time on leaf 3 for cvs. Heartland and Kasota inoculated with P. teres f. teres reflected resistance in these two cultivars. Both pathogens caused less than half the diseased area on leaf 3 as on leaf 2 in all cultivars. A mist period of 48 h tended to obscure the differences on leaf 2 between resistance and susceptibility. In general, there were positive correlations between the two pathogens based on ED50 or ED15. Pyrenophora teres f. maculata resulted in substantially higher ED50 and ED15 values on cvs. Johnston and Heartland, indicating that P. teres f. maculata was less virulent than P. teres f. teres on these cultivars. ED50 and ED15 values could be used to quantitatively differentiate moderately resistant cultivars from susceptible cultivars at the seedling stage.