1992 Volume 58 Issue 5 Pages 671-676
In the fields infested by cucumber wilt fusaria and cultured cucumber, soybean or sorghum for six years continuously, the persistence of the pathogen were observed. The pathogen survived in high population in cucumber and soybean fields, especially kept stable survival in the former field, but it population decreased at every cropping in sorghum field. Although the population decreased by crop conversion without regard to the kind of the crops, it turned to stable within one or two years. The fungus colonized at any time onto roots of cucumber from soil, but its colonization on soybean roots turned to be difficult with growth of the plant. The rhizosphere of sorghum offered uncomfortable condition for their colonization. There were many virulent strains for cucumber wilt from cucumber root colonizer. But many of the strains from other crop roots and field soils were in moderate or weak pathogenicities to cucumber. A lot of chlamydospore were formed by virulent strains in cucumber field and by weak strains in other two fields. It is considered that this characteristic and saprophytic or parasitic ability on root of each crop would send the pathogen toward dominant position in fusarial flora in each continuous cropping field.