Assessing Ramularia leaf spot resistance of spring barley cultivarsin the presence of other diseases

摘要

The expression of Ramularia leaf spot (RLS) resistance of commercial spring barley cultivars and advanced breeding lines was examined, using disease survey data obtained under natural infection conditions in several years and on more than 20 sites in Denmark. The severity levels of leaf diseases other than RLS (powdery mildew, leaf rust, net blotch, physiological leaf spotting) and variety-specific levels of resistance against these were also considered. About 2/3 of the total variation in RLS severity levels could be explained by variables pertaining to environmental disease loads, cultivar susceptibility to foliar diseases other than RLS, actual severity levels of diseases other then RLS and interactions among some of these variables. Of the remaining variation, 1/3 could be explained by additive cultivar main effects and cultivar-specific interactions with the environmental RLS loads. The RLS severity level of cultivars was not independent from their susceptibility to diseases other than RLS and/or from the occurrence of other diseases. Cultivars with mlo-resistance to powdery mildew and cultivars resistant to leaf rust expressed, on average, higher RLS susceptibility than cultivars susceptible to these diseases. The level of susceptibility to diseases other than RLS was positively correlated with the actual severity levels of the respective diseases. The "true" expression of RLS resistance of barley cultivars may thus be masked by the occurrence of other diseases and by cultivar-specific resistance to these. However, data from an inoculated trial that was free of diseases other than RLS show that cultivars with mlo-resistance to powdery mildew indeed are on average more susceptible to RLS than cultivars without this type of resistance.