Molecular and pathological diagnosis of seedborne barley scald disease

Scald of barley caused by Rhynchosporium secalis (Oud.) J. J. Davis is a major foliage disease resulting in yield and quality losses of barley worldwide. The present study focused on developing pathological and molecular diagnostic methods for the seedborne scald and evaluating their potential in studies of the barley scald disease.;Histopathological study of head-infection in barley by R. secalis using light and scanning electron microscopy showed that the scald symptoms were distributed over the lemmas, paleas, awns, glumes and rachises, but were more common on glumes and awns. Fungal growth consisting of hyphae and conidia was restricted to the inner surfaces of lemmas, paleas and glumes in masses surrounded by what appeared to be mucilaginous material. Calcium-containing crystals were observed on the inner surfaces of scald lesions on glumes. This suggests and supports an earlier report that pathogenesis by R. secalis partly involves sequestration of calcium ions from host plants as found in some other pathosystems.;Rhynchosporium secalis was successfully isolated from infected seeds using an agar plating method developed in this study.;Symptomless infection of barley seed was detected in the susceptible cv. Harrington using cultural and PCR-based assays.;The potential of the competitive PCR assay for quantification of seedborne infection by R. secalis in barley was examined. A standard calibration curve for quantification of the levels of seed infection was constructed and used for detecting scald infection in naturally infected barley seeds collected during the 1995 to 1999 growing seasons. The assay showed the potential as an alternative seed health testing method allowing for qualitative as well as quantitative detection of R. secalis in barley seeds.;The differential effects of fungicide-timing and rotation sequences on the severity of head infection of scald were investigated using a competitive PCR assay in comparison with conventional visual disease assessment (VDA). Overall, competitive PCR assay allowed discrimination of the influence of TiltRTM-timing and rotation on head-infection of barley and correlated better with other disease variables and yield losses than VDA. (Abstract shortened by UMI.)...