Application of Environmentally-Friendly Microorganisms for Controlling Fusarium Crown and Root Rot of Tomato

Situation or issue identification: Tomatoes are one of Florida's most important vegetable crops. The fresh-market tomato and tomato transplant production industries are valued together at about $793.5 million annually. Florida produces a large number of tomato seedlings in Speedling or other mini-containers to sell as transplants to garden centers in the northern states or as seedling-transplants to be outplanted by farmers. These seedling-transplants are grown in sterile plug mixes and later outplanted either into fumigated soil where survival is assured by the elimination of most pests and diseases, or they are introduced into competitive soils where the sterile roots are easily infected by plant pathogenic bacteria or fungi. Many fumigant uses are in jeopardy due to deleterious effects on agricultural land, water and air. The first of these fumigants to be removed will be methyl bromide which must be phased out by the year 2000. Therefore, the loss of many fumigants, especially methyl bromide, and the increase in fungicide resistance of widely-used compounds, such as benomyl (Benlate) and metalaxyl (Ridomil), or cancellation of labels means that these chemicals, which are agriculturals' first or only line of defense against many root pathogens, will no longer be available. Consequently, all tomato transplants soon will be grown in more competitive microbial environments. Unfortunately, these transplants are poorly adapted for competing in this hostile environment. However, long term plant survival and root health can be greatly improved by amending plug mix soil or by root inoculating with beneficial organisms. These organisms can provide a multi tactic barrier to plant pathogens by providing an antagonistic soil and a biocontrol shield at the root surface to reduce root disease. Rationale for research support resources: One of the most damaging soilborne pathogens of tomato in Florida is Fusarium oxysporum f. sp. radicis-lycopersici which causes Fusarium crown and root rot (FCRR). Commercial yields have been reported to be reduced by 15 percent. Several control procedures have been attempted for managing FCRR in the greenhouse and field. Fumigation with methyl bromide/chloropicrin has provided good but incomplete control of this disease in the field. However, the classification of methyl bromide as an atmospheric ozone depleter has prompted the United States Environmental Protection Agency to phase out the use of this chemical by the year 2000. Although fungicides such as benomyl or captafol have been demonstrated to be effective, captafol is no longer labeled for usage, and there is an imminent possibility of fungicide resistance. Host resistance to FCRR in commercially acceptable tomato cultivars is limited at present.

Measurable or potential impact in terms of social, economic, and/or environmental factors resulting from expenditure of research support funds: Recently demonstrated that FCRR could be potentially reduced in commercial methyl bromide/chloropicrin fumigated field situations by combining species of Trichoderma and Glomus. Incidence of FCRR was reduced significantly (P=0.05) from 48-57% in the controls to 18-20% for Trichoderma + Glomus combined treatment. Yields of large and extra-large fruit (6.27 cm) increased over the controls 13% to 16%, but were not statistically significantly different from each other. In another study, the incidence of FCRR was reduced by 70% in the controls to 40% for B. subtilis; however these treatments were not significantly different from each other. Other field tests results using this biological treatment were similar in other years too. Whether these results could be translated to nonfumigated field sites as a potential replacement for either methyl bromide or fungicides would need to be tested. Given the aforementioned results already obtained and from other research, it is realistic to expect that biological control of FCRR would function under nonfumigated conditions. These findings also suggest a new potential thrust for suppressing root diseases, i.e., using a combination of more than one biocontrol agent for controlling a root disease has the possibility of reducing soil populations of the pathogen and root necrosis to levels below those experienced with either agent alone. Current and future research is underway to determine if combinations of biologicals are compatible and can promote transplant vigor and growth, and if these biologicals can be a potential replacement for methyl bromide.

Collaborating organizations/agencies and teaching/research/extension partnerships: Agrium, Inc., Bioworks, Inc., Gustafson, Inc.,, Florida Tomato Institute, Fulbright (Council for International Exchange of Scholars), Fundacion BBV, ThermoTriology and USDA-ARS.

For more information contact: Lawrence E. Datnoff