YIELD REDUCTION CAUSED BY A SOIL-BORNE DISEASE OF NAKED, DWARF, AND CONVENTIONAL OAT IN FINLAND

A severe disease occurred in the field plots of naked (cv. Salomon), d warf (cv. Pal), and conventional oat (cvs. Jalostettu maatiainen and S ale) at the Viikki Experimental Farm of the University of Helsinki, Fi nland, in 1994 and 1995. Symptoms were expressed as grayish-brown necr otic areas on the lower leaves which killed plants from the seedling t o heading stage, the effect being cultivar dependent. The proportion o f plants killed contributed to the yield losses. The infection also re sulted in less grains per panicle and lower weight of both panicle and vegetative above-ground biomass. From a total of 57 fungal isolates o btained from infected leaves, Fusarium culmorum (W.G.Sm.) Sacc, and F. sambucinum Fuck. dominated and subsequently caused infection (particu larly foot and root rot) in oat in laboratory tests. These two Fusariu m spp. were considered to be the primary causal agents of the symptoms observed in the field, although other pathogens may have been present . The disease was probably soil-borne. The results of this study sugge sted that the unusually dry and warm weather during late June and in J uly was the principal factor behind the severe disease outbreak.