1a. Objectives (from AD-416):
The fundamental goal of this research program is the development of sustainable methods from the control of soilborne diseases of fruit trees. Thus, the objectives are to define the mechanism(s) of action for brassicaceae seed meals in the control of the pathogen/parasite complex which incites orchard replant disease, and develop and evaluate in the field novel formulations or integrated systems to attain the necessary spectrum of pathogen/parasite suppression for control of orchard replant disease to develop molecular markers for rootstock disease resistance to enhance biocontrol.
1b. Approach (from AD-416):
This program will develop a systems approach to disease management which exploits the biological resources resident to orchard ecosystems and utilizes minimal inputs beyond that commonly employed during orchard renovation or management. This will be achieved through acquiring an understanding of the biological and chemical mechanisms involved in the brassicaceae seed meal induced suppression of the pathogen complex contributing to apple replant disease. New tools will be developed to efficiently monitor fungal community structure in these soils to garner a more complete understanding of the functional elements contributing to disease suppression and the temporal nature of the response. Enhanced efficacy of bio-active plant residues for the control of soilborne pathogens will be obtained by clarifying the role of soil microbial communities in eliciting the inhibitory activity of these plant tissues. Information from these studies will be utilized to develop and field validate biologically sustainable management strategies for control of replant diseases in conventional and organic production systems.
3. Progress Report:
Studies continued to monitor microbial community composition and tree performance of apple plantings established in spring 2010 on multiple replant sites in Washington State which seek to determine the efficacy of composite mustard seed meal amendments in concert with host tolerance for apple replant disease control. Two seed meal formulations were utilized in concert with the highly susceptible apple root stock M9 or Geneva 11 rootstock which is tolerant of the lesion nematode Pratylenchus penetrans. Both seed meal formulations provided disease control that was equivalent or superior to pre-plant soil fumigation based upon microbial analysis and tree growth increment attained over three years at all study sites. The Sunrise orchard autumn seed meal application proved superior to spring applications due to extensive tree mortality resulting from phytotoxicity of the amendment, but spring applications proved to be effective at other study sites. At Stormy Mountain Ranch, a single seed meal formulation applied during the spring was evaluated and was dramatically superior to pre-plant soil fumigation for control of replant disease. The superior tree growth in seed meal treated soils was correlated with superior and prolonged lesion nematode suppression over multiple growing seasons relative to that attained in response to pre-plant soil fumigation. The differential plant response to spring seed meal applications at the study sites were associated with differences in soil type and organic matter content. The Sunrise orchard possessed a sandy soil with very low organic matter (OM) content; which was approximately 30% of that at the Stormy Mountain Ranch test site. In addition, the low OM test site possessed soil microbial populations that were significantly lower. Based upon the level of tree mortality attained in the different seed meal formulation treatments it appears that a prolonged plant back period will be required in sandy soils to allow for degradation of seed meal derived herbicidal chemistries. An assay system was established for examination of gene expression profiles in root tissues in response to challenge by plant pathogenic fungi and oomycetes. Apple seedling root tissues were collected and expression of candidate genes previously shown to function in plant defense responses was monitored under normal and biotic or abiotic stress conditions. DNA sequences of gene families within the jasmonic acid biosynthesis pathway (a pathway associated with plant defense/resistance mechanisms), was utilized to design gene-specific primers which provide the capacity to explicitly monitor expression of the target genes. Tissue-specific expression patterns were initially identified by regular polymerase chain reaction (PCR), and studies were initiated to examine changes in gene expression profiles in root tissues of young seedlings in response to cold treatment by use of quantitative real-time PCR.
1. Induction of nematode suppressive soil system. Effective non-chemical strategies for long-term control of plant parasitic nematodes are desired within the tree fruit producer community due to an absence of nematicides available for post-plant application. Researchers at the Tree Fruit Research Laboratory in Wenatchee, Washington, examined pre-plant application of Brassicaceae seed meal formulations used in conjunction with a virtually impermeable film for control of apple replant disease and suppression of lesion nematode in two organic orchard systems. Seed meal formulations provided multi-year suppression of the lesion nematode densities in apple roots to levels significantly below the no treatment control. Although soil fumigation significantly suppressed densities of this nematode during the initial growing season, extensive re-infestation of fumigated soil by the nematode was observed during the two growing seasons to densities dramatically higher than the control or seed meal treated soils. Nematode suppression in the seed meal treated soil was associated with significant changes in soil biology including increased densities of nematode parasites and predators. This research indicates that a biologically viable alternative to chemical nematicides or soil fumigants can provide extended long-term suppression of plant parasitic nematodes in orchard production systems.
Spies, C.F., Mazzola, M., Botha, W.J., Langenhoven, S., Mostert, L., Mcleod, A. 2011. Molecular analyses of Pythium irregulare isolates from grapevines in South Africa suggest a single variable species. Fungal Biology. 115:1210-1224.