Submitted to: Biological Control
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/27/2014
Publication Date: 6/29/2014
Citation: Shapiro Ilan, D.I., Bock, C.H., Hotchkiss, M.W. 2014. Suppression of pecan and peach pathogens on different substrates using Xenorhabdus bovienii and Photorhabdus luminescens. Biological Control. 77, 1-6.
Interpretive Summary: Fungal diseases or fungus-like diseases can severely reduce the productivity of orchard crops. Chemical fungicides can be extremely effective in controlling these diseases, but these fungicides also may cause harm to the environment, and their usefulness can become limited due to the development of resistance. Therefore, alternative tools for controlling plant diseases are needed. One possibility is to use naturally occurring bacteria or the bacteria’s byproducts (metabolites) to suppress disease. In this laboratory study, we tested the ability of two species of bacteria (Xenorhabdus bovienii and Photorhabdus luminescens) to suppress two diseases of pecan (caused by Fusicladium effusum and Phytophthora cactorum) and one peach disease (caused by Armillaria tabescens). The treatments suppressed all three crop diseases and suppression was observed on leaf surfaces as well as in soil. In general, concentrated bacterial metabolites were more effective than the bacteria themselves, except both bacteria and metabolites were effective in controlling Phytophthora cactorum. 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 Xenorhabdus and Photorhabdus metabolites or bacteria broths for suppression of plant 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.