Submitted to: Nematropica
Publication Type: Abstract Only
Publication Acceptance Date: 4/9/2000
Publication Date: N/A
Citation: Interpretive Summary: 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. Orchard sites suppressive to PTSL and the ring nematode have been identified in South Carolina. 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. During a 3-year monitoring period of ring nematode suppressive peach orchard sites, the nematode population remained below detection limits as compared to nonsuppressive sites. Steam treatment of the suppressive soil eliminated the factor responsible for inhibiting nematode reproduction. Results indicate that 7 bacteria were responsible for inhibiting ring nematode multiplication. The cells and cell-free filtrate of one isolate (BG33) kills nematode eggs. Egg-killing activity appears to be associated with salicylic acid production by BG33. Under orchard conditions, ring nematodes were significantly suppressed for up to 18 months post-soil solarization and BG33 inoculation vs. nonsolarized/non-BG33. These data provide useful insights into the potential use of BG33 and soil solarization as an alternative to chemical control of the ring nematode on PTSL sites in the Southeast.
Technical Abstract: The ectoparasitic migratory ring nematode, Mesocriconema (Criconemella) xenoplax has been shown to play an important role in the induction of the disease syndrome, Peach Tree Short Life (PTSL), in the southeastern United States. Field sites suppressive to PTSL, and the ring nematode, have been identified in South Carolina. During a three-year monitoring period, ring populations in these sites remain at or below detection limits while populations rose to greater than 1,400 ring nematodes/100cc soil in adjacent sites in the same orchard. In green house testing, steam treatment of these soils eliminated suppressiveness, whereas small amounts of non-steamed suppressive soil added to steamed soil inhibited M. xenoplax multiplication. Seven fluorescent pseudomonad strains from the suppressive field soil were found to inhibit ring nematode multiplication. Cells and cell-free culture filtrate of one of these isolates, P. synxantha BG33, kills the ring nematode eggs when applied to the eggs within 5 days of deposition. Application of BG33 to trees in newly established orchards planted into solarized soil significantly reduced nematode reproduction. Up to 18 months post-solarization and BG33 inoculation, ring nematode populations remained significantly below populations in non solarized/non-BG33 inoculated control field sites. This level of nematode control is equivalent to that observed with methyl bromide fumigation. Using Tn5 mutagenesis, we have identified 5 genetic loci in BG33 that are involved in egg-kill factor production. The Tn5 insertion sites in these mutants have been cloned and sequenced and gene sequence homologies have been determined. Egg-killing activity appears to be associated with salicylic acid production by BG33.