Sensitivity of resistance to net blotch in barley

The aim of this study was to demonstrate various methods of analysing termi nal net blotch, Pyrenophorateres Drechs. f. teres Smedeg., severity data fr om 15 spring barleys, Holdeum vulgare L., grown in Finnish official variety trials in five environments. The analyses have been developed and used pri ncipally by plant breeders for assessing crop yield, but lead themselves to use by plant pathologists. Pyrenophora teres is the major barley phytopath ogen in Finland and improved resistance to it is sought. Joint regression a nalysis (JRA) and an additive main effects and multiplicative interaction ( AMMI) model were used to investigate the data. Statistically significant ge notype by environment (GE) interaction for resistance was indicated, and th is included qualitative (crossover) interactions among genotypes over envir onments. A stable, non-sensitive, response to net blotch over environments, combined with a low mean score for terminal severity of the disease charac terized the six-row barley 'Thule' which showed statistically significant c rossover interaction only with 'Tyra'. 'Kustaa' exhibited the lowest mean t erminal net blotch severity, but was relatively sensitive to net blotch. 'A rve' exhibited severe terminal net blotch in all environments, was relative ly sensitive to environment and exhibited no crossover interaction with oth er genotypes. AMMI analysis appeared to represent a useful method for analy sing these disease severity data, facilitating the selection of useful sour ces of resistance. Plots of AMMI-adjusted mean net blotch severities agains t first principal component axis (PCA) scores were informative for differen tiating genotype response over environments, and are therefore potentially useful to plant pathologists and barley breeders seeking to gauge and subse quently improve the resistance status of barley to net blotch.