Scald on gramineous hosts in Iran and their potential threat to cultivated barley

Abstract

There are five described Rhynchosporium species, Rhynchosporium commune, R. secalis, R. agropyri, R. orthosporum and R. lolii, that cause scald diseases on Poaceae. This study used morphological (conidial shape and size) and phylogenetic analyses of two loci (the internal transcribed spacer region (ITS) and β-tubulin (TUBB)) to identify Rhynchosporium species and their host ranges in Iran. Despite the large variation observed for Rhynchosporium conidial dimensions, the phylogenetic analyses of the ITS region and concatenated ITS and TUBB loci revealed that all isolates from wild grasses in Iran belong to R. commune. R. commune was isolated from Hordeum murinum ssp. glaucum, Hordeum vulgare ssp. spontaneum, Lolium multiflorum and Avena sativa in Iran. A. sativa has only been reported from Iran as a host for R. commune. After cross inoculation, A. sativa was considered as the most resistant host showing the lowest susceptibility to R. commune isolates. Of the grass hosts tested, H. vulgare ssp. spontaneum was the most susceptible. The most aggressive isolate across all tested hosts was isolated from Hordeum murinum ssp. glaucum. Cross-infection of the R. commune isolates from all hosts onto uncultivated grasses and cultivated barley suggests the potential of the uncultivated grasses as inoculum sources for cultivated barley epidemics and pathogen evolution. Thus, management of uncultivated grasses in the vicinity of barley fields should assist in managing the disease on cultivated barley.