Netzer, D., Div. of Plant Pathology, ARO, The Volcani Center, Bet Dagan, Israel

Results of a comparative test oflocal isolates of Fusarium oxysporum f. sp. niveum with isolates from abroad indicate the existence of a highly virulent race of this fungus in Israel. All these isolates were found also pathogenic to resistant cultivars from the U.S.A. When inoculum density was tested, a one-hundredfold higher fungus population was required for extensive wilt of watermelon seedlings in freshly infested sterilized soil compared with the same soil kept dry for three months. In naturally infested soil, where almost 100% of the plants were infected toward the end of the season, the lowest count of the fungus population (400 propagules/g soil) was comparable to the inoculum density required for total wilt of watermelon seedlings in infested sterilized soil. © 1976 Springer Science + Business Media B.V.