The pathogenicity and importance of seed-borne infection by Bipolaris sorokiniana on barley in Finland

Seed-borne infection by Bipolaris sorokiniana decreased the percentage germination of barley seeds and the emergence of seedlings. Infection levels were higher in non-germinated than in germinated seeds. Seed treatment with organomercurial fungicide or imazalil improved the percentage emergence but a low number of diseased seedlings still remained in the crops. The fungus caused a reduction in grain yields in most experiments and also decreased their value as sowing seed, if the weather conditions were favourable for compute disease expression. Yield losses in greenhouse experiments varied from 7.2 to 38.5 % and in the field from 5 to 11 %, and showed a strong correlation with the infection levels in the seed stocks. Higher losses were associated with the six-row cultivars. Organomercury seed treatment resulted in a slight but in significant increase in yields but it was able to prevent an occurrence of secondary infection in the crop resulting in a lower seed infection levels of the grain. In field experiments in Inari (69° N.L.) seed-borne inoculum could be demonstrated clearly to be the only source of a severe disease outbreak. The inoculum remaining in the soil was capable of initiating soil-borne infection of barley seedlings during the following two growing seasons.