Abstract
In Japan, ragi (finger millet, Eleusine coracana (L.) Gaertn.) had been raised as one of the millets in a slash-and-burn culture in mountain areas since the preceding period of rice cultivation, but its cultivation has run short in the present century. Recently ragi was grown for trial as fodders in different localities, where an outbreak of blast disease caused by Pyricularia sp. occurred in 1973. Seed carried the pathogen as mycelia within the tissue of a membranous pericarp. The pericarp became dark-brown in color and adhered to the seed coat. The percentage of diseased seeds from different localities and cultivars was 5 to 46. Mycelia in the pericarp remained viable at -10C and R.H. 30% for 8 years and more. An infection chain from seed to top was demonstrated at 25C under humid conditions in a growth-chamber. The pathogen attacked each part of the floweret; pericarp, upper and lower glumes>lemma, palea, rachilla, and rachis. These diseased organs of the seed which were contaminated also became an inoculum source in the field. Lesions on a leaf-sheath became an inoculum source after cutting. Seedling blight by the pathogen occurred at 10 to 40% of discolored seeds. Alternaria sp. and Curvularia sp. also caused seedling blight. Complete control was afforded by treatment with benomyl (50%); 500ppm solution soaking for 6hr or 0.5% (w/w) coating. Isolates of Pyricularia sp. from Eleusine coracana, E. indica, E. africana and E. floccifolia were pathogenic to ragi and not pathogenic to rice. Isolates from 17 gramineous species including rice and Zingiber mioga were not pathogenic to ragi. Isolates from E. coracana, E. indica and Setaria viridis var. minor were pathogenic to Lolium multiflorum, Festuca elatior var. arundinacea, Phalaris arundinacea, Anthoxanthum odoratum, maize, barley and oats. Severe outbreaks of blast in virginal localities of ragi cultivation was attributable to the introduction of diseased seeds. Transmission of the pathogen from grasses, especially from E. indica, seems possible, but more assessment of distribution of the pathogen is necessary to conclude it. As regards the nomenclature of ragi Pyricularia, it is suggested that reexamination of the species concept is needed, considering morphology, Pathogenicity and mating relationship.
