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Oral: Biological and Cultural Disease Management


Pseudomonas sp associated with Smilax bona-nox display strong activity against Phytophthora spp
G. ALI (1), A. El-Sayed (2), D. Norman (2), M. Brennan (3) (1) University of Florida, U.S.A.; (2) University of Florida/ Institute of Food and Agricultural Sciences, U.S.A.; (3) MREC/University of Florida/ Institute of Food and Agricultural Sciences, U.S.

Smilax bona-nox is a perennial weed, which is found in natural landscapes and forests throughout the southwestern U.S. S. bona-nox displays disease tolerance and vigorous growth, which could be partially attributed to beneficial plant-associated microorganisms. In this report, we recovered 44 bacterial isolates from roots and shoots of S. bona-nox. Based on 16S rRNA gene sequencing, these isolates belonged to 14 different genera. Antimicrobial screens showed that two of these isolates, EA6 and EA14, displayed strong inhibition of Phytophthora parasitica. Phylogenetic analyses based on the rpoD gene revealed that EA6 and EA14 belonged to the genus Pseudomonas. EA6 and EA14 did not produce biofilm, but produced bio-surfactants, volatile hydrogen cyanide and sulfur compounds. Biochemical fractionation of the volatile and secreted products of these two isolates for identifying the bioactive compound(s) revealed that volatile and organic extracts did not display any anti-Phytophthora activity. In contrast, salt precipitation of the aqueous phase revealed strong anti-Phytophthora activity, which was abolished by autoclaving or proteinase K treatments. Protein fractionation analyses suggest that the antimicrobial activity of EA6 is likely due to synergistic interaction of a mixture of glucanolytic enzymes. In conclusion, these two Pseudomonas isolates can be used for organically controlling Phytophthora diseases in crops.