Location: Fruit and Nut Research2009 Annual Report
1a. Objectives (from AD-416)
Develop improved nematode management strategies based on cultural and biocontrol approaches for suppression of ring and (or) root-knot nematode and related peach disease complexes and elucidate the interactive effects and (or) incidence among key nematode pests, pathogenic fungi, and rootstocks to improve the understanding of host susceptibility associated with peach and pecan tree decline problems, such as Peach Tree Decline and Pecan Replant Disease.
1b. Approach (from AD-416)
Evaluate selected rotation crop for suppression of root-knot nematode as an alternative to fumigation; investigate natural products associated with rotation crop for effect on nematode egg hatch and vermiform-life stage survival; investigate solarization alone and in combination with the application of a cocktail of biocontrol agents for nematode management when delivered through irrigation; characterize the suppressive effects of biocontrol agent towards the Pecan and Peach root-knot nematodes; develop new knowledge regarding interactive effects among nematode pests and (or) pathogenic fungi as associated with peach and (or) pecan replant disease; and evaluate advanced Prunus germplasm for resistance to continuous root-knot nematode pressure under field conditions. Resources will support research already taking place on this project. This includes development of strategies or approaches to minimize the economic impact of nematodes and other pathogens on peach and pecan. Work involves ground covers, alternatives to chemical nematicides, and biological agents to reduce nematode populations in soils.
3. Progress Report
The research outlined in this project contributes to the overall mission of ARS to develop new technology and knowledge in order to solve deciduous tree fruit and nut problems of high national priority. This research addresses selected rotation crops, the use of bacteria biocontrol agents, the evaluation of advanced rootstock selections in microplots, and evaluation of interactions between nematodes and (or) Armillaria root rot fungus that will result in advanced knowledge and improved pre- and postplant nematode management recommendations and tree survival on PTSL or replant sites. The proposed research project is in accord with two ARS Strategic Program Plans as follows: 1) 188.8.131.52 - Pathogen Interactions with Host Plants and 2) 184.108.40.206 - Plant Disease and Nematode Control. PROGRESS: In FY 2009, 1) One and 2-year preplant crop rotation sequences were completed and preplant fumigation treatment established to study the suppression of nematode infestation, thus promoting tree growth on a root-knot nematode infested field site prior to replanting orchard back to peaches. Nematode population densities determined in respective plots; 2) Crude root exudates from rotation grass has been challenged against root-knot nematode second-stage juveniles (J2) under laboratory conditions. Results inconclusive at this time. Plan to challenge exudate against egg stage. Also evaluated grass against three other root-knot nematode species under greenhouse conditions at ARS-Byron and ARS-Beltsville locations; 3) The effect of soil solarization alone and in combination with the cocktail of biocontrol agents on suppression of ring nematode and tree mortality continues. Nematode population dynamics, tree growth, and PTSL tree death data recorded. Winter wheat planted in respective plots. Preplant soil solarization appears to be as good as preplant methyl bromide in suppression of ring nematodes to date; 4) Field microplot experiment to study best P. penetrans isolate for biocontrol of the pecan root-knot nematode was initiated at ARS-Byron location. Treatments included i) nematode-alone, ii) biocontrol agent-alone, iii) nematode + biocontrol agent, and iv) control. All microplots planted to Elliott pecan seedlings; 5) Tree growth & symptomatology data recorded as related to Armillaria root rot fungus nematode interaction field microplot study. No results to report at this time; and 7) Nematode population dynamics, peach tree growth and symptomatology data recorded among rootstock treatments with and without continuous root-knot nematode pressure in field microplots. Nematode soil populations are currently greatest under Lovell vs. Guardian rootstock. Fruit yield was recorded for the first time.
1. Host Status of Transgenic Plum Lines to Mesocriconema xenoplax: The ring nematode, Mesocriconema xenoplax, is associated with making peaches more susceptible to PTSL tree death. The use of genetic engineering to increase disease resistance in agricultural crops is developing into an acceptable and complementary technique to traditional disease management methods. Evaluating genetically transformed plum rootstocks for resistance to the ring nematode is important in determining the potential use of these rootstocks as a management tool for the peach industry in the southeastern United States. Results indicate that all three plum lines supported ring nematode reproduction, but line 5D suppressed nematode populations more than the other two lines. These data provide useful insights into the potential utilization of a genetically transformed plum rootstock to manage ring nematode in peach in the southeastern United States.