Submitted to: Journal of Microbiology and Biotechnology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/12/2004
Publication Date: 12/15/2004
Citation: Slininger, P.J., Burkhead, K.D., Schisler, D.A. 2004. Antifungal and sprout regulatory bioactivities of phenylacetic acid, indole-3-acetic acid, and tyrosol isolated from the potato dry rot suppressive bacterium Enterobacter cloacae S11:T:07. Journal of Industrial Microbiology and Biotechnology 31:517-524. Interpretive Summary: Fungal dry rot is one of the most serious postharvest potato diseases, causing yearly crop losses estimated at $100-$500 million. Over 80% of the causative fungal pathogen strains are now resistant to the only chemical registered for postharvest use on tubers for human consumption. In the U.S., CIPC is a chemical applied to inhibit sprouting in over 50% of the potato crop, but its use faces increasing restrictions due to health concerns. A beneficial soil bacterium found in healthy potato fields has been shown to significantly reduce both dry rot and sprouting in potato storages. The metabolites which accumulated in production cultures of the beneficial bacterium, given a variety of nutritional environments, were identified and characterized according to their ability to suppress disease and sprouting. The results showed that application of a combination of metabolites rather than single metabolites allowed for best disease reduction. One of the metabolites exhibited the ability to suppress both disease and sprouting. Furthermore, the composition of metabolites in cultures was dependent on nutrients available. These findings potentially impact the potato industry because they support the continuing development of beneficial soil bacteria as environmentally friendly means to control both sprouting and fungal diseases with a single treatment applied to tubers entering storage.
Technical Abstract: Enterobacter cloacae S11:T:07 (NRRL B-21050) is a promising biological control agent which has significantly reduced both fungal dry rot disease and sprouting in lab and pilot potato storages. The metabolites phenylacetic acid (PAA), indole-3-acetic acid (IAA), and tyrosol (TSL) were isolated from S11:T:07 liquid cultures provided three different growth media. The bioactivities of the metabolites were investigated via TLC bioautography of antifungal activity, wounded potato assays of dry rot suppressiveness, and cored potato eye assays of sprout inhibition. Relative accumulations of PAA, IAA, and TSL in cultures were nutrient dependent. For the first time, IAA, TSL, and PAA were shown to have antifungal activity against the dry rot causative pathogen G. pulicaris and to suppress dry rot infection of wounded potatoes. Disease suppression was optimal when all three metabolites were applied in combination. Dosages of IAA which resulted in disease suppression, also resulted in sprout inhibition. These results suggest the potential for designing culture production and formulation conditions to achieve a dual purpose biological control agent able to suppress both dry rot and sprouting of stored potatoes.