Submitted to: Journal of Nematology
Publication Type: Abstract Only
Publication Acceptance Date: 6/28/2000
Publication Date: N/A
Citation: Interpretive Summary: Ring nematodes are widely distributed throughout the world with certain species considered to be economically important to the stone fruit industry. Probably the most studied ring nematode species on Prunus is Mesocriconema xenoplax. This ring nematode is the only plant-parasitic nematode that has been associated with the peach tree short life (PTSL) disease complex in the southeastern United States. Tree loss due to PTSL in South Carolina alone was estimated at over $5 million per year. New alternatives to chemical control (i.e., biological control) that are less hazardous to man and also more environmentally safe must be found to protect peach trees from this ring nematode. In the early 1990's, a bacterium [Pseudomonas sp (GB33R)] was isolated from a nematode suppressive soil in South Carolina that was later shown to inhibit ring nematode multiplication under laboratory and greenhouse conditions. The efficacy of BG33R on suppression of the ring nematode population was then investigated in conjunction with soil solarization under peach orchard conditions from 1996-00. Results indicate that ring nematode populations remained at or below detection limits for about 18 months in soil solarized as compared to nonsolarized plots. Additionally, five Tn5 egg kill mutants have been generated and the insertion site in each mutant cloned and sequenced. These data provide useful insights into the potential use of BG33R and soil solarization as a pre- and postplant alternative to chemical control of the ring nematode on PTSL sites in the Southeast.
Technical Abstract: The ring nematode, Mesocriconema xenoplax, is an ectoparasitic migratory nematode that has been shown to induce Peach Tree Short Life in the southeastern U.S. Seven fluorescent Pseudomonas spp capable of inhibiting M. xenoplax multiplication have been isolated from soil sites that suppress PTSL and ring nematode multiplication. One of these seven, Pseudomonas spp BG33R, inhibits M. xenoplax multiplication in-vivo and egg hatch in-vitro. M. xenoplax populations on peach seedlings inoculated with BG33R and planted into solarized field plots remained at or below detection limits for nearly 18 months post inoculation and solarization. Soil solarization alone also generated a microbial community suppressive to the development of the ring nematode. M. xenoplax populations on non-inoculated trees planted into non-solarized soil reached levels of approximately 500 nematodes/100cc soil. Five Tn5 egg-kill negative mutants of BG33R have been generated. The Tn5 insertion site in each mutant has been cloned and sequenced. DNA sequence analysis has revealed a high degree of homology to several genes of interest that will be discussed in relation to their potential involvement in egg-kill factor (ekf) production. The BG33R Tn5 ekf negative mutants are also protease and salicylic acid negative and express twice the amount of fluorescent siderophore as the wild type parent. The possible commercial use of BG33R in the control of ring nematodes in peach orchards will be discussed.