BIOLOGICAL-CONTROL OF FUSARIUM-OXYSPORUM F-SP ASPARAGI BY APPLYING NONPATHOGENIC ISOLATES OF FUSARIUM-OXYSPORUM

Root rot severity of asparagus plants grown in sterilized field soil i noculated with Fusarium oxysporum f. sp. asparagi (Foa) was reduced by more than 50% wizen the soil was precolonized by each of 13 non-patho genic (np) isolates off. oxysporum originating from asparagus roots or field soils. In a greenhouse experiment, application of six np isolat es to naturally infested field soil was followed by a 23-49% decrease of disease severity, depending on the isolate. One of them, Fo47 origi nating from Fusarium suppressive soil in France, was applied to field plots infested with Foa. Foa root rot was not suppressed in asparagus plants grown for 1 year in these plots. Pathogenic and np isolates ext ensively colonized the root surface and isolates of both types infecte d the roots of asparagus plants grown in sterilized field soil, with s ignificant differences among the np isolates. Inoculation of sterilize d field soil with np isolates reduced germination of Foa chlamydospore s by 43-64% depending on rite isolate used. It is concluded that np is olates of F. oxysporum can suppress asparagus root rot caused by Foa i n naturally infected field soil. The differences for root colonization capacity among the np isolates imply that selection for this trait mi ght reveal isolates that perform better under field conditions.