2011 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.
The research outlined in this project contributes to the overall mission of ARS to develop new technology and knowledge to solve deciduous tree fruit and nut problems of high national priority. This research addresses selected rotation crops, use of bacteria biocontrol agents, evaluation of advanced rootstock selections in microplots, 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 Peach Tree Short Life on replant sites.
Tree growth and yield data were recorded and analyzed. Results indicate that tree growth in the 1-yr and 2-yr grass rotation soil and fumigated soil are significantly larger than trees in unfumigated soil. Trees in both grass rotation schemes are not different from those in the fumigated soil. First year yield data indicate that total fruit weight and number of fruit per tree in both grass rotation and fumigated treatments were significantly greater than trees in unfumigated soil.
Crude root exudate from rotation grass has been challenged against root-knot nematode J2 stage and eggs under laboratory conditions in ARS-Beltsville. Results indicate that egg hatch and J2 mobility are suppressed by root exudate and shoot extract solution is suppressive to egg hatch. Experiments evaluating grass against four root-knot nematode species under greenhouse conditions at ARS-Byron and/or ARS-Beltsville locations have been completed and two peer review papers have been published.
Studies of the effect of soil solarization alone and in combination with biocontrol agents and/or wheat on suppression of ring nematode and tree mortality were completed. Results indicate that solar-wheat treated soil was as effective as preplant methyl bromide fumigation in increasing tree survival from Peach Tree Short Life Disease for at least 6 years after orchard establishment. Manuscript submitted to Plant Disease.
Field microplot experiment to study best P. penetrans isolate for biocontrol of the pecan root-knot nematode was continued at ARS-Byron. Excessive flooding of microplots from 3 months continual rainfall occurred in fall and may have compromised experiments. Tree growth data was recorded, but no significant differences noted. Foliage rated for severity of Mouse-ear symptoms and results indicate that Mouse-ear was most severe in presence of nematode-alone, intermediate in the control, and least severe in nematode + biocontrol agent.
Tree growth and symptomatology data recorded as related to Armillaria root rot fungus vs. nematode interaction field microplot study. Results are not substantiating last year's data.
Nematode populations, tree growth, yield and symptomatology data were recorded among treatments with and without continuous root-knot nematode pressure. Nematode soil populations are remaining greatest under Lovell vs. Guardian rootstock regardless of continuous weed presence. Tree growth and yield data were analyzed and the results were inconclusive.
Solarization is as good as fumigation in suppressing ring nematode. The ring nematode predisposes peach trees to Peach Tree Short Life and bacteria spot and requires controls that are less hazardous to man and the environment. The evaluation of a bacteria biocontrol cocktail for controling ring nematode, in conjunction with and without soil solarization or wheat from 2004-2010, found that the biocontrol cocktail did not suppress the ring populations, whereas soil solarization plus wheat was as effective as methyl fumigation in increasing tree survival for at least five years after orchard establishment. This demonstrates that soil solarization is a viable preplant alternative to chemical control of ring nematode, thus, providing farmers a new pest management tool.
Groundcover suppresses root-knot and root-lesion nematode populations. In recent years peach growers in the Southeast have been faced with economic hardships which make it difficult to afford fumigation; thus,a nonchemical alternative to preplant chemical control of nematode pests is needed. Tall fescue grass cultivars evaluation for susceptibility to the Southern, Peanut and Javanese root-knot nematodes, ring nematode, and root-lesion nematode at ARS-Byron, GA and the Northern root-knot nematode at ARS-Beltsville, MD, found tall fescue cultivars are either poor or nonhosts for most root-knot and root-lesion nematodes. This work provides essential baseline data needed for determining whether tall fescue is a viable alternative to preplant chemical control of certain root-knot and root-lesion nematodes under field conditions.
Nyczepir, A.P., Meyer, S.L. 2010. Host status of endophyte-infected and noninfected tall fescue grass to Meloidogyne spp. Journal of Nematology. 42(2):151-158.
Nyczepir, A.P. 2011. Host suitability of an endophyte-friendly tall fescue grass to Mesocriconema xenoplax and Pratylenchus vulnus. Nematropica. 41:45-51.