Pyrenophora teres and Rhynchosporium secalis Establishment in a Mediterranean Malt Barley Field: Assessing Spatial, Temporal and Management Effects

Malt barley is one of the promising crops in Greece, mainly due to high yields and contract farming, which have led to an increase in malt barley acreage. Net form net blotch (NFNB), caused by Pyrenophora teres f. teres, and barley leaf scald, caused by Rhynchosporium secalis, 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 estimate the epidemiology of NFNB and leaf scald in a barley disease-free area when the initial inoculation of the field occurs through infected seeds, (ii) to explore the spatial dynamics of disease spread under the interaction of the nitrogen rate and genotype when there are limited sources of infected host residues in the soil and (iii) to assess the relationship among the nitrogen rate, grain yield, quality variables (i.e., grain protein content and grain size) and disease severity. It was confirmed that both NFNB and leaf scald can be carried over from one season to the next on infected seed under Mediterranean conditions. However, the disease severity was more pronounced after the barley tillering phase when the soil had been successfully inoculated, which supports the hypothesis that the most important source of primary inoculum for NFNB comes from infected host residue. Increasing the rate of nitrogen application, when malt barley was cultivated in the same field for a second year in a row, caused a non-significant increase in disease severity for both pathogens from anthesis onwards. However, hotspot and commonality analyses revealed that spatial and genotypic effects were mainly responsible for hiding this effect. In addition, it was found that the effect of disease infections on yield, grain size and grain protein content varied in relation to the genotype, pathogen and stage of crop development. The importance of crop residues in the evolution of both diseases was also highlighted.