Pyrenophora teres and Rhynchosporium secalis infections in malt barley as influenced by genotype, spatial and temporal effects and nitrogen fertilization

Net form net blotch (NFNB) and barley leaf scald are among the most important barley diseases worldwide and particularly in Greece. Their occurrence in malt barley can exert a significant negative effect on malt barley grain yield and quality. An experimental trial across two growing seasons was implemented in Greece in order i) to assess the epidemiology of NFNB and leaf scald in a barley disease free area when the initial inoculation of field occurs through infected seeds, and ii) to further explore the relationship among nitrogen rate, grain yield, quality variables (i.e. grain protein content and grain size) and disease severity and epidemiology. It was demonstrated that both NFNB and leaf scald can be carried over from one season to the next on infected seed under Mediterranean conditions. However, disease severity was more pronounced after barley tillering phase when soil had been successfully inoculated first. When nitrogen rate and genotype were the main sources of variation the epidemiology assessment was implemented with hotspot and Anselin Local Moran9s I analysis. It was found that the location of hotspots was modified during growing season. Soil and plant variables were assessed for the explanation of this variability. According to commonality analysis the effect of distance from the locations with the highest disease infections was a better predictor of disease severity (for both diseases) compared to nitrogen rate during pre-anthesis period. However, disease severity after anthesis was best explained by nitrogen rate only for the most susceptible cultivars to NFNB. The effect of disease infections on yield, grain size and grain protein content varied in relation to genotype, pathogen and stage of crop development. The importance of crop residues on the evolution of both diseases was also highlighted.