Ability of nonpathogenic Fusarium oxysporum Fo47 to protect tomato against Fusarium wilt

The nonpathogenic Fusarium oxysporum strain Fo47 is an effective biocontrol agent against Fusarium wilt of tomato caused by F. oxysporum f. sp. lycopersici. Inoculant delivery protocols in which plants were exposed to Fo47 prior to challenge with the pathogen, so as to promote the strain's ability to induce resistance to Fusarium wilt in tomato, were assessed. In rockwool microcosms, the biocontrol efficacy of Fo47 (inoculated at sowing) against F. oxysporum f. sp. lycopersici Fo18 (race O) was not improved following a second inoculation of the biocontrol strain at transplanting (i.e., when plants became exposed to the pathogen) or using inoculum levels of Fo47 higher than 10(4) conidia/ml of nutrient solution, In natural soil microcosms (with Fo47 applied into potting mix prior to sowing and to roots at transplanting), effective control of Fusarium wilt required inoculum levels of 10(5) conidia of Fo47/ml, Strain Fo47 was also studied in greenhouse microplots in which soil was artificially infested with the pathogenic strain Fo18, Fo47 delayed the progression of the disease in each of the two years and also improved final plant health in the second year. The protective effect of Fo47 resulted in a significant increase in the yield of first-grade tomatoes in the first year. Treatments did not influence yield in the second year. The results of this investigation illustrate how a biocontrol fungus can be used at a moderate inoculum level to obtain disease control under commercial conditions. It is hypothesized that this was achieved by making use of the ability of the biocontrol agent to induce resistance to Fusarium wilt in tomato. (C) 1999 Academic Press.