Location: Fruit and Tree Nut ResearchTitle: Suppression of pecan scab and phytophthora using symbiotic bacteria and their byproducts Author
Submitted to: Pecan Grower
Publication Type: Trade Journal
Publication Acceptance Date: 4/17/2014
Publication Date: 1/1/2014
Citation: Shapiro Ilan, D.I., Bock, C.H., Hotchkiss, M.W. 2014. Suppression of pecan scab and phytophthora using symbiotic bacteria and their byproducts. Pecan Grower. 25(4):66-74. Interpretive Summary: Fungal diseases or fungus-like diseases such pecan scab and Phytophthora can severely reduce crop productivity. Alternative tools for controlling plant diseases are needed. One possibility is to use naturally occurring bacteria or the bacteria’s byproducts (also called metabolites) to suppress disease. In this laboratory study, we tested the ability of two species of bacteria (Xenorhabdus bovienii and Photorhabdus luminescens) and their metabolites to suppress pecan scab (caused by Fusicladium effusum) and Phytophthora disease (caused by Phytophthora cactorum). The X. bovienii metabolite treatment was as efficacious as a commercial chemical fungicide (fenbuconazole) in reducing scab on pecan terminals. The P. luminescens metabolite also caused reduced sporulation, but the bacteria cultures by themselves had no effect. In contrast, all bacteria cultures and metabolites suppressed growth of Phytophthora on pecan leaves. A patent has been issued for using the bacteria metabolites against peach and pecan diseases. This study provides a basis for further research on the use of bacteria and metabolites for suppression of pecan diseases.
Technical Abstract: Prior research indicated the ability of concentrated metabolites from Xenorhabdus spp. and Photorhabdus spp. to suppress a variety of peach and pecan diseases in vitro, and on detached pecan leaves or terminals. In the current study, our objectives were to 1) determine if bacterial broths (in addition to concentrated metabolites tested previously) have suppressive ability and 2) determine if metabolites or bacterial broths are active in a soil medium. In laboratory studies, two pathogens of pecan (Fusicladium effusum and Phytophthora cactorum) and one peach pathogen (Armillaria tabescens) were tested for susceptibility to X. bovienii (SN) and P. luminescens (VS) bacterial broths or concentrated metabolites on three different substrates. Treatments were applied to lesions of F. effusum, on terminals to ascertain any suppressive effect on sporulation, to A. tabescens in soil to determine effect on survival of mycelia, and to lesions caused by P. cactorum on pecan leaf surfaces to assess any reduction in lesion development. The X. bovienii metabolite treatment was as efficacious as a commercial fungicide (fenbuconazole) in reducing sporulation of F. effusum on pecan terminals. The P. luminescens metabolite treatment also caused reduced sporulation relative to water and acetone controls but bacterial broths had no effect. In contrast, all bacterial broth and metabolite treatments suppressed lesion growth caused by P. cactorum. However, in soil, only the P. luminescens metabolite treatment was suppressive to A. tabescens (this is the first report of Photorhabdus or Xenorhabdus toxicity to Armillaria spp.). This study provides a basis for further research on the use of Xenorhabdus and Photorhabdus metabolites or bacterial broth for suppression of pecan and peach diseases.