2011 Annual Report
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 and Develop molecular markers in rootstock resistance or 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.
Microbial and growth analyses were conducted at new plantings of apple established in spring 2010 on three different organic orchard (Sunrise, Stormy Mountain and Tukey) replant sites in Washington state to evaluate the efficacy of composite mustard seed meal amendments in concert with host tolerance for the control of apple replant disease (ARD). Disease control and tree performance was dependent upon the seed meal formulation utilized and exhibited a modicum of site specificity. Two seed meal formulations when utilized in concert with the highly susceptible apple root stock M9, and the Geneva 11 rootstock which is tolerant of the parasitic 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 growth increment attained over two years at all study sites. At 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. The differential plant response to spring amendments at the study sites was associated with differences in soil type and organic matter content. The Sunrise orchard possessed a sandy soil with very low organic matter content; OM content was approximately 30% of that at the other two test sites. 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 microbial degradation of active chemistries.
Based upon our previous detection of significant variation in susceptibility to the fungal pathogen Rhizoctonia solani within an apple rootstock population from the USDA-ARS rootstock breeding program in Geneva, NY, segments of the population were included in a follow up evaluation to more clearly characterize the segregating factors that explain this variation.
Alternative to soil fumigation for control of apple replant disease. ARS researchers at the Tree Fruit Research laboratory in Wenatchee, Washington evaluated the efficacy of brassicaceae seed meals for the control of apple replant disease and the effects of such treatments on the causal pathogen complex, tree growth and fruit yield were examined over a five year period in conventional production systems. When applied independently, all pre-plant seed meal treatments or a post-plant mefenoxam failed to enhance tree growth or control disease to the level attained in response to soil fumigation. Postplant mefenoxam treatments revealed that failure of seed meal amendments to enhance tree growth and yield when used independently was due, primarily, to increased apple root infection by Pythium spp. in Brassica napus and Sinapis alba seed meal–amended soils, and by Phytophthora cambivora in Brassica juncea–amended soil. When used in conjunction with a postplant application of mefenoxam, B. juncea and S. alba seed meal pre-plant soil amendments were as effective as preplant 1,3-dichloropropene-chloropicrin soil fumigation in terms of disease control, vegetative tree growth, and five-year fruit yields of Gala/M26 apple. As these trials utilized the highly susceptible rootstock M26, the results demonstrate that this integrated strategy is a viable alternative to soil fumigation for the control of apple replant disease in conventional production systems.
Replant disease control in organic orchards. Effective non-fumigant and non-chemical strategies for controlling apple replant disease long have been desired within the tree fruit producer community. ARS 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 replant disease in three commercial/research organic orchard systems. Seed meal formulations provided levels of disease control and tree growth response that were equivalent or superior to that obtained in response to pre-plant soil fumigation, but autumn rather than spring applications were required in orchards possessing a sandy soil texture to avoid potential phytotoxicity. This research indicates that a biologically viable alternative to pre-plant soil fumigation is attainable for the control of apple replant disease in organic and conventional production systems.
Handiseni, M., Brown, J., Zemetra, R., Mazzola, M. 2011. Herbicidal activity of Brassicaceae seed meal on wild oat (Avena fatua), Italian ryegrass (Lolium multiflorum Lam.), Redroot pigweed (Amaranthus retroflexus L.) and Prickly lettuce (Lactuca serriola). Weed Technology. 25:127-134.
Tewoldemedhin, Y., Mazzola, M., Mostert, L., Mcleod, A. 2011. Cylindrocarpon species associated with apple tree roots in South Africa and their quantification using real-time PCR. European Journal of Plant Pathology. 129:637-651.
Spies, C., Mazzola, M., Wilhelm, J., Van Der Rijst, M., Mostert, L., Mcleod, A. 2011. Oogonal biometry and phylogenetic analysis of the Pythium vexans species group from woody agricultural hosts in South Africa reveal distinct groups within this taxon. Fungal Biology. 115:157-168.
Mazzola, M., Zhao, X. 2010. Brassica juncea seed meal particle size influences chemistry but not soil biology-based suppression of individual agents inciting apple replant disease. Plant Soil. 337:313-324.
Mazzola, M. 2010. Management of resident soil microbial community structure and function to suppress soilborne disease development. In: Reynolds, M., editor. Climate Change and Crop Production. CABI, Wallingford, UK. p. 200-219.
Tewoldemedhin, Y.T., Mazzola, M., Botha, W.J., Spies, C., Mcleod, A. 2011. Characterization of fungi (Fusarium and Rhizoctonia) and oomycetes (Phytophthora and Pythium) associated with apple orchards in South Africa. European Journal of Plant Pathology. 130:215-229.
Lamprecht, S.C., Tewoldemedhin, Y.T., Calitz, F.J., Mazzola, M. 2011. Evaluation of strategies for the control of canola and lupin seedling diseases caused by Rhizoctonia anastomosis groups. European Journal of Plant Pathology. 130:427-439.
Spies, C., Mazzola, M., Mcleod, A. 2011. Characterisation and detection of Pythium and Phytophthora species associated with grapevines in South Africa. European Journal of Plant Pathology. 131:103-119.
Tewoldemedhin, Y.T., Mazzola, M., Labuschangne, I., Mcleod, A. 2011. A multi-phasic approach reveals that apple replant disease is caused by multiple biological agents, with some agents acting synergistically. Soil Biology and Biochemistry. 43:1917-1927.