Comparison of diagnostic methods, virulence and aggressiveness analysis of Pyrenophora spp. in pre-basic seeds in the barley fields

Plant diseases caused by seed-borne pathogens cause yield and quality losses and threaten seed production of barley (Hordeum vulgare L.) and food security. The aim of this study was to compare common seed health methods for the diagnosis and detection of Pyrenophora species, and to investigate cell wall degrading enzymes (CWDEs), virulence and aggressiveness of the isolates obtained from pre-basic barley seed fields in Iran. Comparing common seed health methods showed that more fungal isolates were recovered from seeds using the agar plate method compared to freezing blotter, osmotic, embryo count, and seed washing tests. A total of 7 fungal species from 5 genera were identified from 30 different samples of various Iranian barley cultivars. Based on morphological and molecular characteristics, the fungi were identified as Pyrenophora graminea, P. teres f. teres, P. teres f. maculata, Alternaria alternata, Fusarium culmorum, F. graminearum, Rhynchosporium commune and Ustilago nuda f. sp. hordei. This study has shown that barley seed samples carry a wide diversity of fungi. The results showed that the 57 % of the total samples were found to be infected by seed-borne fungi. Among the genera, Pyrenophora was the most abundant fungus. Diverse levels of virulence and aggressiveness were observed for various isolates of Pyrenophora species. Analyzing the activity of CWDEs produced by isolates revealed that xylanase activity was more important than cellulase activity for the virulence of Pyrenophora isolates and enzyme activities affect levels of virulence and aggressiveness of isolates. Therefore, these findings suggest that activity levels of xylanase are correlated with variation in virulence and aggressiveness of Pyrenophora isolates on seedings. This is the first report identifying the seed-borne fungi of Iranian barley cultivars in pre-basic barley seed fields of Iran.