University of Helsinki, Department of Plant Pathology
This study was carried out on Rhynchosprium secalis (Oud.) J. J. Davis occurring on spring barley, winter rye and couch grass (Agropyron repens (L.) PB) in Finland. The results were obtained from samples of barley (c. 860 samples) and rye (c. 200 samples) gathered in fields during the growing season throughout the country in 1971 1973. The samples (c. 170 samples) of Agropyron repens were collected in fields and the borders of fields. The fungi of all the samples were examined by microscope and cultures and inocolation tests were used as well. Rhynchosporium secalis was observed to occur commonly on spring barley throughout the country from Helsinki to Lapland. The fungus was observed in about 30 per cent of the fields and in below 60 percent of the localities examined. Leaf blotch was commoner on six rowed barley than on two-rowed barley. The fungus sometimes attacked a field in great profusion. R. secalis was observed in below 50 per cent of the winter rye samples and in below 70 per cent of the localities examined. The fungus occurred commonly in the southern part of Finland and was found also in Lapland (Inari, 69° N, 27°E). Spores of the fungus were most abundant in the leaves of rye in spring and in early summer. R. secalis was observed rather scarce (in over 10 per cent of fields and in over 25 per cent of the localities examined) on Agropyron repens throughout the country. A high degree of host specialisation has been found within the species R. secalis. Two isolates from spring barley and from winter rye were pathogenic to their original host only.
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