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Title: Relative potency of culture supernatants of Xenorhabdus and Photorhabdus spp. on growth of some fungal phytopathogens

item HAZIR, SELCUK - Adnan Mederes University
item Shapiro Ilan, David
item Bock, Clive
item HAZIR, CANAN - Adnan Mederes University
item LEITE, LUIS - Instituto Biologicio - Brazil
item Hotchkiss, Michael - Mike

Submitted to: European Journal of Plant Pathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/28/2016
Publication Date: 8/1/2016
Citation: Hazir, S., Shapiro Ilan, D.I., Bock, C.H., Hazir, C., Leite, L., Hotchkiss, M.W. 2016. Relative potency of culture supernatants of Xenorhabdus and Photorhabdus spp. on growth of some fungal phytopathogens. European Journal of Plant Pathology. 146(2):369-381.

Interpretive Summary: The productivity of orchard crops such as pecan and peach can be severely curtailed by plant diseases such as scab, root rot, brown rot, etc. Chemical fungicides can be effective in controlling these diseases. However, due to environmental and regulatory concerns, as well as the buildup of fungicide resistance, safe alternative methods of control must be sought. We tested the ability of bacteria to control serious fungal diseases of pecan and peach. The bacteria we used are natural symbionts (partners) of beneficial insect-killing nematodes. Specifically, we investigated the potential of cell-free by-products produced by different bacteria to suppress anthracnose, root rot, brown rot, peach scab and pecan scab. Of all the treatments tested, a bioactive natural chemical produced by the bacteria called trans-Cinnamic acid (TCA), and by-products of bacteria called Xenorhabdus szentirmaii caused the greatest amount of suppression in the plant diseases tests. Our results indicate the substantial potential for using TCA or Xenorhabdus bacteria cell free supernatants as natural environmentally safe bio-fungicides.

Technical Abstract: We evaluated the potency of 10% v/v cell-free culture supernatants of cultures of the bacteria X. bovienii, X. nematophila, X. cabanillasii, X. szentirmaii, P. temperata, P. luminescens (VS) and P. luminescens (K22) against Fusicladium carpophilum (peach scab), Fusicladium effusum (pecan scab), Monilinia fructicola (brown rot), Glomerella cingulata (anthracnose) and Armillaria tabescens (root rot). A bioactive compound derived from Photorhabdus bacteria, trans-cinnamic acid (TCA), was also compared with the bacterial filtrates. Fungal colony size based on manual measurements was compared for accuracy to measurements taken by image analysis. Supernatants of Xenorhabdus spp. exhibited stronger suppressive effects on spore germination and vegetative growth when compared with Photorhabdus spp. Overall, TCA was the most effective treatment; vegetative growth was completely inhibited by 10% TCA (w/v). TCA treatments also suppressed spore germination of F. carpophylium and F. effussum by approximately 90%. The efficacy of supernatants varied among Xenorhabdus species depending on the species tested, but X. szentirmaii filtrates tended to cause greater inhibition relative to the other bacteria supernatants. Manual measurement of colony diameter required at least two replicate estimates (which provide more precise data) of the colony to avoid a type II error. Area measurements were slightly underestimated when based on ruler measurements. Supernatants of Xenorhabdus spp., Photorhabdus spp, or 10%TCA did not cause any phytotoxic effects when applied to various plant species in the greenhouse. Our results indicate the potential of using TCA or Xenorhabdus cell free supernatants as bio-fungicides.