ANTIMYCOTIC ACTIVITY OF XENORHABDUS-BOVIENII (ENTEROBACTERIACEAE) METABOLITES AGAINST PHYTOPHTHORA-INFESTANS ON POTATO PLANTS

Soluble organic metabolites produced by phase one of Xenorhabdus bovie nii strain A2 were tested for their antimycotic activity against selec ted plant pathogenic fungi and for their phytotoxicity. The metabolite s were extracted with ethyl acetate from the supernatant of 96-h-old X . bovienii cultures in tryptic soy broth. They were fungicidal to Phyt ophthora infestans at 0.1 mg/mL on rye agar but only partially inhibit ed Pythium ultimum and Rhizoctonia solani on potato dextrose agar in p etri plate tests. In potted plant tests, the antimycotic metabolites w ere applied to the foliage of 4- to 5-week-old potato plants (cv. Norc hip) as a protectant spray at concentrations of 5.0 and 10.0 mg/mL. Th e 10.0 mg/mL treatments inhibited (P greater than or equal to 0.05) bl ight development 7 d after inoculation with only 4.0% of the inoculate d leaflets showing symptoms of successful fungal infection, compared w ith 100% in the controls. The percentage of inoculated leaflets with b light symptoms was reduced to 24.0% on plants treated with 5.0 mg/mL o f antimycotic metabolites. Phytotoxicity was observed on plants treate d with the antimycotic metabolites, and the phytotoxic damage increase d with increasing concentrations. The visible phytotoxic responses on potato plants treated with up to 10.0 mg/mL did not spread, and subseq uent growth appeared normal. The selectivity of the antimycotic metabo lites of X. bovienii against the three test fungi, its phytotoxic prop erties and the potential of these metabolites for fungal disease contr ol are discussed.