Progress 08/15/08 to 08/14/12

Outputs
OUTPUTS: Studies were completed which determined the modes of action functional in the Brassicaceae seed meal induced control of the various elements that comprise the causal pathogen complex inciting apple replant disease. The relative importance of biological and chemical mechanisms, the operative biological entities, the temporal dynamics of the disease control response, and the effect on long-term organic system resilience to pathogen/parasite recolonization of organic orchard soils was determined. The effect of soil type, season of application, apple rootstock genotype, seed meal formulation and duration of plant back period on potential for phytotoxicity, disease control, tree growth and yield were determined in three trials conducted in organic orchard systems. These field trials were used as a resource for numerous educational, grower tour and international meetings including the annual Washington State University Sunrise Orchard Field tour, Washington State University Department of Horticulture and Department of Plant Pathology field courses and served as a major component of the field program conducted at the 2nd International Organic Fruit Research Symposium, where the sites were toured as part of the presentation "Advances in application protocol and Brassica seed meal formulation for management of replant disease". Findings from these studies were presented by invitation at numerous grower and industry supported conferences, and not limited to tree fruits, including the Organic Session of the Washington State Horticultural Association, 2nd International Organic Fruit Research Symposium, the Mid-Columbia Cherry Day research symposium sponsored by Oregon State University, the Ecoraz Symposium sponsored by the Washington Red Raspberry Association, Snohomish County Focus on Farming Conference, the Western Region SARE, Washington State University Center for Sustaining Agriculture and Natural Resources, and the National Integrated Pest Management Symposium. The work conducted in this program has fostered new collaborations with scientists, both nationally and internationally, at the University of California-Santa Cruz, the University of California-Davis, Wageningen University the Netherlands and Stellenbosch University South Africa. The technology developed in this program is being evaluated for use in other plant production systems and the seed meal formulation developed is being made available. This project led to the hosting and mentoring of numerous undergraduate students, graduate students, as well as visiting scientists from Spain, Kenya and Egypt. PARTICIPANTS: Mark Mazzola, the PD, managed the overall research program including the conduct of field trials and the dissemination of findings to the grower and research community. This project served as the vehicle to provide training to numerous graduate students of the plant/microbial sciences including Ms. Muditha Weerakoon (Washington State University), Ms. Shashika Hewavitharana (Washington State University), Mr. Maxwell Handiseni (Univ. of Idaho), Mr. Aaron Agostini (Sonoma State University) and Ms. Manuela Vincente Domingues (Cordoba University, Spain). In addition, undergraduate students including Ms. Irene Mendoza, Ms. Laurie Bazan (University of Washington, and Mr. Alec Schmidt (Central Washington University obtained training in soil biology and organic management systems through this program. The program also provided training and development to two post-doctoral research associates. TARGET AUDIENCES: The program provided practicum experience for two undergraduate students (Ms. Irene Mendoza and Ms. Laurie Bazan) from the local Hispanic population, which is characteristically under-represented in the field of plant/microbial science research fields. Field days were conducted at the Washington State University Sunrise orchard and the Stormy Mountain Ranch commercial orchard to demonstrate the efficacy of seed meal formulations for the control of apple replant disease. These events were attended by growers, industry representatives, graduate students and the general public. Additional events were conducted in these orchard trials as part of formal Washington State University horticultural classes. Findings from these trials were also presented to growers at the International Fruit Tree Association conference, the Annual Meeting of the Washington State Horticultural Association, the Washington State Tree Fruit Research Commission Review, a Washington Red Raspberry Commission sponsored symposium on ecological farming, the Focus on Farming conference sponsored by Snohomish County Washington, and the Mid-Columbia Cherry Research Symposium sponsored by Oregon State University. PROJECT MODIFICATIONS: Not relevant to this project.

Impacts
The findings obtained in these studies will significantly improve the ability to predictably utilize Brassicaceae seed meal amendments for the control of apple replant disease, and other soil-borne diseases, in organic crop production systems. Our findings clearly established that disease control in response to these plant-based amendments is not exclusively a function of chemical mechanisms but that altered soil biology plays a significant role in disease control, with the active mechanism varying in a time dependent manner. It was also established that the use of an individual seed meal is unlikely to yield significant benefit as these materials exhibit differential effects on populations of diverse soil-borne pathogen populations. As a result, novel seed meal formulations were developed in this program that enabled effective control of fungal, oomycete and nematode pathogens/parasites. Optimal strategies for the application of these materials were developed. Factors that were demonstrated to be of importance included seed meal formulation, soil moisture, seed meal particle size, duration of plant back period, soil type, and the use of a virtually impermeable film after incorporation of the seed meal amendment. All of these factors were defined and an effective systems-based approach to the use and application of the materials was established. Field trials established that pre-plant application of the Brassicaceae seed meal system provided control of apple replant disease as effectively as the use of pre-plant soil fumigation. Furthermore, application of the seed meal system resulted in the establishment of a soil microbial community that exhibited significantly greater resilience against plant pathogen and parasite re-colonization relative to that observed in fumigated soils. Moreover, fruit yields obtained were consistently and significantly higher in seed meal treated soil relative to that attained in fumigated soil. These studies have made available a seed meal formulation and application protocol that can effectively control a diversity of soil-borne pathogens and parasites in organic crop production systems.

Publications

• Mazzola, M. 2011. Potential of biofumigation for soilborne pest control in strawberry. pp 47.1-47.2, In, Proceedings Annual International Research Conference on Methyl Bromide Alternatives and Emissions Reductions. MBAO, Fresno, CA.
• Spies, C. F. J., Mazzola, M., and McLeod, A. 2011.Characterization and detection of Pythium and Phytophthora species associated with grapevines in South Africa. European Journal Plant Pathology 131:103-119.
• Lamprecht, S. C., Tewoldemedhin, Y. T., Calitz, F. J. and 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. F., Mazzola, M., Botha, W. J., Van der Rijst, M., Mostert, L. and McLeod, A. 2011. Oogonial biometry and phylogenetic analyses of the Pythium vexans species group from woody agricultural hosts in South Africa reveal distinct groups within this taxon. Fungal Biology 115:157-168.
• Tewoldemedhin, Y. T., Mazzola, M., Labuschagne, I. and McLeod, A. 2011. Towards understanding the etiology of apple replant disease in South Africa using a multiphasic approach. Soil Biology & Biochemistry. 43:1917-1927.
• Tewoldemedhin, Y. T., Mazzola, M., Mostert, L., and 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.
• Mazzola, M. 2011. Advances in Brassica seed meal formulation for apple replant disease control. pp 6.1-6.4, In, Proceedings Annual International Research Conference on Methyl Bromide Alternatives and Emissions Reductions. MBAO, Fresno, CA. 2011.
• Mazzola, M. 2011. Active management of soil microbial communities to limit soilborne disease development in strawberry production systems. In, Annual Report to the California Strawberry Commision. pp137-147.
• Tewoldemedhin, Y. T., Mazzola, M., Botha, W. J., Spies, C. F., and McLeod, A. 2011. Characterization of fungi (Fusarium and Rhizoctonia) and oomycetes (Phytophthora and Pythium) associated with apple orchards in South Africa. European Journal Plant Pathology 130:215-229.
• Handiseni, M., Brown, J., Zemetra, R., and Mazzola, M. 2011. Herbicidal activity of Brassicaceae seed meal on wild oat (Avena fatua), Italian rye grass (Lolium multiflorum), redroot pigweed (Amaranthus retroflex) and prickly lettuce (Lactuca serriola). Weed Technology 25:127-134.
• Mazzola, M. 2010. Management of resident soil microbial community structure and function to suppress soilborne disease development. pp 200-219, In, M. Reynolds (ed.) Climate Change and Crop Production. CABI, Wallingford, UK. 2010.
• Mazzola, M. and 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 and Soil 337:313-324.
• Mazzola, M. and Brown, J. 2010. Efficacy of brassicaceous seed meal formulations for the control of apple replant disease in organic and conventional orchard production systems. Plant Disease 94:835-842.
• Mazzola, M., de Bruijn, I., Cohen, M. F., and Raaijmakers, J.M. 2009. Protozoan-induced regulation of cycliclipopeptide biosynthesis is an effective predation defense mechanism for Pseudomonas fluorescens. Applied and Environmental Microbiology 75:6804-6811.
• Mazzola, M. 2009. Active manipulation of native soil microbial community structure and function to suppress soilborne diseases. Pages 1-11. In, Proceedings, 19th Southern Africa Symposium on Soils and Soilborne Plant Diseases. Agricultural Research Council, Plant Protection Research Institute, Stellenbosch, South Africa.
• Mazzola, M. 2009. Resident biology restricts Macrophomina phaseolina in brassicaceous seed meal amended soil. pp 100.1-100.3, In, Proceedings Annual International Research Conference on Methyl Bromide Alternatives and Emissions Reductions. MBAO, Fresno, CA.
• Mazzola, M. 2009. Non-fumigant management of apple replant disease in organic and conventional systems. pp 47.1-47-4, In, Proceedings Annual International Research Conference on Methyl Bromide Alternatives and Emissions Reductions. MBAO, Fresno, CA.
• Pusey, P. L., Stockwell, V.O., and Mazzola, M. 2009. Epiphytic bacteria and yeasts on apple blossoms and their potential as antagonists of Erwinia amylovora. Phytopathology 99:571-581.
• Izzo, A. and Mazzola, M. 2009. Hybridization of an ITS-based macroarray with ITS community probes for characterization of complex communities of fungi and fungal-like protists. Mycological Research 113:802-812.
• Mazzola, M., Brown, J., Zhao, X., Izzo, A., and Fazio, G. 2009. interaction of brassicaceous seed meal and apple rootstock on recovery of Pythium spp. and Pratylenchus penetrans from roots grown in replant soils. Plant Disease 93:51-57.
• Wissuwa, M., Mazzola, M. and Picard, C. 2009. Novel approaches in plant breeding for rhizosphere-related traits. Plant and Soil 321:409-430.
• Hoagland, L., Carpenter-Boggs, L., Granatstein, D., Mazzola, M., Smith, J., Peryea, F., and Reganold, J. P. 2008. Impact of floor management strategies on nitrogen fertility and biological soil quality in newly established organic apple orchards. Biology & Fertility of Soils 45:11-18.
• Hoagland, L., Carpenter-Boggs, L., Reganold, J., and Mazzola, M. 2008. Role of native soil biology in brassicaceae seed meal induced weed suppression. Soil Biology & Biochemistry 40:1689-1697.
• Mazzola, M. and Manici, L. M. 2012. Apple Replant Disease: Role of microbial Ecology in Cause and Control. Annual Review of Phytopathology 50:45-65.
• Raaijmakers, J. M., and Mazzola, M. 2012. Diversity and natural functions of antibiotics produced by beneficial and pathogenic soil bacteria. Annual Review of Phytopathology 50:403-424.
• Weerakoon, D.M.N., Reardon, C. L., Paulitz, T. C., Izzo, A. D., and Mazzola, M. 2012. Long-term suppression of Pythium abappressorium induced by Brassica juncea seed meal amendment is biologically mediated. Soil Biology & Biochemistry 51:44-52.
• Handiseni, M., Brown, J., Zemetra, R., and Mazzola, M. 2012. Use of Brassicaceous seed meals to improve seedling emergence of tomato and Pepper in Pythium ultimum infested soils. Archives of Phytopathology and Plant Protection 45:1204-1209.
• Mazzola, M., Reardon, C. L., and Brown, J. 2012. Initial species composition and brassicaceae seed meal type influence extent of Pythium-induced plant growth suppression. Soil Biology & Biochemistry 48:20-27.
• Lamprecht, S. C., Tewoldemedhin, Y. T., Hardy, M., Calitz, E. J., and Mazzola, M. 2011. Effect of cropping system on composition of Rhizoctonia populations recovered from canola and lupin in a winter rainfall region of South Africa. European Journal of Plant Pathology 13:305-316.
• Spies, C.F.J., Mazzola, M., Botha, W. J., Langenhoven, S., Mostert, L., and McLeod, A. 2011. Pythium irregulare isolates from grapevines in South Africa represent one phylogenetic species that may include aneuploids or polyploids. Fungal Biology 115:1210-1224.

Progress 08/15/10 to 08/14/11

Outputs
OUTPUTS: Tree growth in response to brassicaceae seed meal amendments at three orchard replant field trials established at three different commercial and research organic orchards were monitored. The efficacy of different brassicaceae seed meal formulations on control of the pathogen complex that incites apple replant disease was determined at these three sites. The effect of plant plant back period on phytotoxicity and the interaction with apple rootstock genotype was assessed. Findings from these trials was disseminated to the producer community at various grower meetings including the International Fruit Tree Association meeting, at the annual meeting of the Washington State Horticultural Association, and at the annual scientific review of the Washington Tree Fruit Research Commission. Interest in this model as a potential soil-borne disease control strategy in other cropping systems was evidenced by invitation to discuss findings at the ECORAZ symposium sponsored by the Washington Red Raspberry commission, Western Region SARE and the Washington State University Center for Sustaining Agiculture and Natural Resources. This work as fostered new collaborations with scientists at the University of California-Santa Cruz and University of California-Davis in which the use of this technology for soil-borne pest control in strawberry production systems will be evaluated. This project has resulted in the hosting and mentoring of numerous graduate and undergraduate students currently conducting studies at the University of Washington, Washington State University, Sonoma State University, and Stellenbosch University (South Africa). PARTICIPANTS: Mark Mazzola, the PD, managed the overall research program including conduct of field trials and dissemination of findings to the grower and research community. Ms. Muditha Weerakoon, graduate student was trained through the conduct of this program and completed requirements for the MSc degree in plant pathology through the course of this program. She conducted studies concerning the development of long-term soil suppressiveness towards Pythium abappressorium in response to Brassica juncea seed meal amendment. Ms. Shashika Hewavitharana has commenced graduate studies in plant pathology and is contributing to this research program. Ms. Xiaowen Zhao conducted studies that addressed the effect of seed meal particle size on generation of biologically active chemistries in response to Brassica juncea seed meal amendment and control of plant pathogens and parasites. Mr. David Granatstein from the Washington State University Center for Sustaining Agriculture has provided extension resources for the dissemination of findings from this program to growers at various meetings. This project has served as a vehicle to provide training to a number of graduate students at various institutions including Mr. Maxwell Handiseni (University of Idaho), Mr. Aaron Agostini (Sonoma State University) and Ms. Manuela Vincente Domingues (Cordoba University, Spain), as well as the PDs own graduate students. In addition, undergraduate students Ms. Irene Mendoza and Ms. Laurie Bazan currently attending the University of Washington obtained training in soil biology and organic management systems through this research program. TARGET AUDIENCES: This program provided practicum experience to two undergraduate students (Ms. Irene Mendoza and Ms. Laurie Bazan) from the local Hispanic population, which is characteristically under-represented in the field of plant/microbial science research fields. Field days were conducted at the Washington State University Sunrise Orchard and at the Stormy Mountain Ranch Commercial Orchards to demonstrate the efficacy of seed meal formulations for the control of apple replant disease. These events were attended by growers, industry representatives, graduate students and the general public. Additional events were conducted in these orchard trials as part of formal Washington State University horticultural classes. Findings from these trials were also presented to growers at the International Fruit Tree Association conference, the annual meeting of the Washington State Horticultural Association, the Washington Tree Fruit Research Commission review and a Washington Red Raspberry Commission sponsored symposium on ecological farming. PROJECT MODIFICATIONS: Not relevant to this project.

Impacts
Data obtained from field trials to date will significantly improve the ability to predictably utilize brassicaceae seed meal amendments for the control of apple replant disease in organic orchard production systems. In these field trials, the seed meal formulations developed were shown to provide control of root populations of the plant parasitic nematode Pratylenchus penetrans (lesion nematode) and root infection by Pythium spp. as effectively as pre-plant soil fumigation. Correspondingly, apple tree performance in response to seed meal amendment over two growing seasons at two of the orchard sites is comparable to that attained in response to soil fumigation and at the third site, tree growth in response to seed meal amendment was 100% greater than the response in fumigated soil. However, in soils possessing low overall microbial activity significant tree death was observed when soils were treated in the spring of planting rather than the fall prior to planting. In addition, significant seed meal formulation by rootstock genotype responses have been observed. These findings will enable application of a prescription-based model for use in determining appropriate seed meal formulation based on soil type and apple rootstock when applying these materials for replant disease control. Long-term control of of Pythium root infection in response to pathogenic Pythium spp. was shown to be dependent upon transformations in orchard soil fungal communities. Such an approach is important in the irrigated orchard systems found throughout the west as various oomycetes, including Pythium and Phytophthora, are introduced into the orchard environment through irrigation water.

Publications

• Tewoldemedhin, Y. T., Mazzola, M., Mostert, L., and 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
• Tewoldemedhin, Y. T., Mazzola, M., Botha, W. J., Spies, C. F., and McLeod, A. 2011. Characterization of fungi (Fusarium and Rhizocotonia) and oomycetes (Phytophthora and Pythium) associated with apple orchards in South Africa. European Journal of Plant Pathology 130:215-229.
• Handiseni, M., Brown, J., Zemetra, R., and Mazzola, M. 2011. Herbicidal activity of Brassicaceae seed meal on wild oat (Avena fatua), Italian rye grass (Lolium multiflorum), redroot pigweed (Amaranthus retroflex) and prickly lettuce (Lactuca serriola). Weed Technology 25:127-134.

Progress 08/15/09 to 08/14/10

Outputs
OUTPUTS: Studies were completed concerning the effect of brassicaceae seed meal particle size on the efficacy of these amendments for the control of soilborne fungal pathogen Rhizoctonia solani and the parasitic nematode Pratylenchus penetrans (lesion nematode). The relative contribution of chemical and biological mechanisms in seed meal induced suppression of the oomycete plant pathogen Pythium abapressorium was determined. Three new orchard plantings were established to evaluate the capacity of seed meal formulations and host tolerance to provide effective control of apple replant disease. The effect of rootstock, seed meal formulation, and application period (autumn prior to planting or spring of planting) were evaluated. Results of these trials were reported to growers at the annual meeting of the Washington State Horticultural Association. Results of these trials were also disseminated to the producer and scientific community through field days held at the Washington State University Sunrise Orchard, the site of one field trial. In addition, these trials were used as an educational tool as part of the summer field tour conducted by graduate students in the Department of Crop and Soil Sciences at Washington State University. This project resulted in the hosting and mentoring of numerous graduate students currently conducting studies at Washington State University, the University of Idaho, Sonoma State University, and the University of Cordoba (Spain). PARTICIPANTS: Mark Mazzola, the PD, managed the overall research program including the conduct of field trials. Ms. Mudithat Weerakoon, graduate student, has conducted research concerning the development of suppressiveness toward the oomycete plant pathogen Pythium abappressorium in response to Brassica juncea seed meal amendment. Ms. Xiaowen Zhao conducted studies that addressed the impact of B. juncea particle size on generation of allyl isothiocyanate and subsequent control of the fungal plant pathogen Rhizoctonia solani. Mr. David Granatstein has provided extension resources for the dissemination of findings from this program to growers at various meetings. This project has served as a vehicle to provide training to a number of graduate students at various institutions including Mr. Maxwell Handiseni (Univ. of Idaho), Mr. Aaron Agostini (Sonoma State Univ.) and Ms. Manuela Vincente Dominguez (Cordoba University). This research program has also resulted in contact with commercial operations that are attempting to develop effective formulations of brassicaceae seed meals for use in organic strawberry and vineyard production systems. TARGET AUDIENCES: Field days were conducted at the Washington State University Sunrise Orchard to demonstrate the efficacy of seed meal formulations for the control of apple replant disease. These events were attended by growers, industry representatives, and research scientists. Additional events were conducted at this orchard trial as part of formal Washington State University classes in which the justification for such research and the findings of these trials were presented to undergraduate and graduate students. Findings from these trials were also presented to growers at the annual meeting of the Washington State Horticultural Association and the Washington Tree Fruit Research Commission. PROJECT MODIFICATIONS: Not relevant to this project.

Impacts
Field trials established during the current fiscal year will significantly improve our ability to effectively utilize brassicaceae seed meals for the control of soilborne plant pathogens in organic agricultural production systems. Of utmost significance is the finding that seed meal (SM) formulations consisting of Brassica juncea/Brassica napus or B. juncea/Sinapis alba SM when utilized with an effective tarping system can provide an initial growth response in apple on replant sites that is equivalent to that obtained through soil fumigation. Initial relative tree growth response did not differ among seed meal formulations, however the level of weed control was superior with the B. juncea/S. alba formulation. Of particular note was the effect of seed meal application date on growth of apple. At two orchards possessing soils with organic matter content ranging from 3.2-4.3% spring applications of seed meal were highly effective and yield a growth increment that was equivalent to or greater than that attained through soil fumigation. In contrast, when similar studies were conducted in a soil possessing low organic matter content (1.2%) and correspondingly lower microbial activity, autumn seed meal application was effective in controlling replant disease but spring application resulted in high levels of tree mortality. Significant mortality was observed irrespective of apple rootstock and was marginally higher in the B. juncea/S. alba treatment compared to the B. juncea/B. napus treatment. The herbicidal nature of these seed meals is well documented, but differential plant back periods required in different soil types has not previously been established. Such information is critical to the effective use of seed meal amendments in a disease control or fertility management program. Seed meal particle size was found to have significant effects on disease control efficacy, but the response was pathogen specific and affected chemistry-based but not biology-based mechanisms. Emission of ally isothiocyanate (AITC) from B. juncea SM-amended soil was initiated earlier and reached higher maximal concentrations in soils amended with fine particle (<1 mm dia) than coarse particle (2-4 mm dia) size. This corresponded with the level of R. solani suppression obtained with B. juncea SM through chemical mechanisms; fine particle size but not coarse particle size B. juncea SM suppressed apple root infection. Biological mechanisms associated with B. juncea SM-induced control of R. solani were not affected by seed meal particle size. Our findings demonstrate that particle size will affect the efficacy of B. juncea SM soil amendment for the control of R. solani AG-5, but will do so only through effects on chemistry-and not biologically-based mechanisms of pathogen suppression. Studies demonstrated that control of Pythium abappressorium through B. juncea SM amendment was also dependent upon chemical and biological mechanisms. The amendment was capable of inducing soil suppressiveness towards this pathogen of apple within two weeks of application. Preliminary evidence suggests that soil fungi are functional in the observed disease suppression.

Publications

• Weerakoon, M., and Mazzola, M. 2010. Brassica juncea seed meal amendment induces long-term suppressiveness to Pythium abapressorium under enclosed and open soil incubation conditions. Phytopathology 100:S134.
• Mazzola, M. 2010. Management of resident soil microbial community structure and function to suppress soilborne disease development, chapter 11 in M.P. Reynolds (ed.) Climate Change & Crop Production, CAB International Oxfordshire, UK, p. 200-218.
• Mazzola, M. and Zhao, X. 2010. Brassica juncea seed meal particle size influences chemistry but not soil biology-based suppression of individual agents inciting apple replant disease. DOI 10.1007/s11104-010-0529-5

Progress 08/15/08 to 08/14/09

Outputs
OUTPUTS: Studies were conducted to assess the effect of brassicaceous seed meal particle size on the structure and function of soil microbial communities and the generation of the active chemistry allyl isothiocyanate in response to soil amendment with Brassica juncea seed meal. Studies were initiated to determine the relative contribution of chemistry and soil biology to the suppression of the oomycete apple root pathogen Pythium spp. observed in response to brassicaceous seed meal amendments. Plantings were established at the Columbia View research and demonstration orchard and a commercial organic apple orchard on replant ground which will assess the efficacy of brassicaceous seed meal amendments for the control of apple replant disease. Initial brassicaeous seed meal soil amendments were applied at the Sunrise organic orchard and follow up treatments will be applied in the spring of 2010. This site will be planted with a susceptible and tolerant apple rootstock in May 2010 to evaluate the potential of seed meal formulations in concert with host tolerance for control of this disease complex. A field day describing this research project was conducted at the Sunrise orchard in July 2009. This project resulted in hosting or mentoring graduate students at Washington State University, the University of Idaho, and Sonoma State University. PARTICIPANTS: Mark Mazzola, the PI, managed the overall research program and conducted the field trials described. Ms. Muditha Weerakoon, graduate student, has conducted research on the effect of particle size on populations of Pythium spp. and disease control. Ms. Xiaowen Zhao conducted studies concerning the effect of particle size on populations of resident Streptomyces spp. and emissions of allyl isothiocyante from seed meal amended soils. Ms. Sheila Ivanov and Ms. Jing Yang provided technical support in the conduct of these studies. Dr. Gennaro Fazio, USDA-ARS, Geneva, New York, has provided apple rootstock genotypes that will continue to be used in these studies. Mr. David Granatstein has provided extension resources for the dissemination of this material to growers at various meetings. Training was provided to three graduate students and one postdoctoral research associate. TARGET AUDIENCES: Information was provided to grower groups through field days and presentations at grower annual meetings. PROJECT MODIFICATIONS: Not relevant to this project.

Impacts
To date, data from field trials have demonstrated that the use of individual brassicaceous seed meal soil amendments, when utilized with the highly susceptible apple rootstock M26, will not be compatible for control of apple replant disease in organic orchard production systems. However, data from the trial conducted in a commercial organic apple orchard which employed a novel composite seed meal formulation with the same highly susceptible apple rootstock indicate that this treatment has significant potential. The composite seed meal amendment controlled all elements of the pathogen complex inciting replant disease at this study site including Pythium spp., Phytophthora cactorum, Cylindcarpon destructans, Rhizoctonia spp. and the lestion nematode Pratylenchus penetrans. To date, growth of trees (increase in trunk diameter) established in seed meal amended soils is equivalent to that attained for trees cultivated in soils receiving preplant treatment with the fumigant 1,3-dicloropropene-chloropicrin. Seed meal species and particle size had significant effects on components of the microbial community known to function in suppression of the fungal pathogen Rhizoctonia solani. Brassica napus and Brassica juncea seed meals consistently elevated resident Streptomyces spp. to densities that were significantly higher than that attained with Sinapis alba seed meal amendments. Fine particles of Brassica juncea seed meal generated significantly higher levels of the active chemistry allyl isothiocyante than did coarse particles of the same seed meal when added to a soil system. These findings are important as both chemistry and biology contribute to control of the pathogen complex that incites apple replant disease.

Publications

• Mazzola, M. 2009. Active manipulation of native soil microbial community structure and function to suppress soilborne diseases. Pages 1-11 in, Proc. 19th Annual Interdisciplinary Symposium on Soilborne Diseases. Stellenbosch, South Africa.
• Mazzola, M., Brown, J. and Fazio, G. 2009. INTERACTION OF BRASSICACEOUS SEED MEAL AND ROOTSTOCK ON RECOVERY OF PRATYLENCHUS PENETRANS FROM ROOTS OF APPLE GROWN IN REPLANT ORCHARD SOILS. Abstract book Annual Meeting of the Society of Nematologists, Burlington, VT.
• X. Zhao, Y. Tewoldemedhin, A. Mcleod, and M. Mazzola. 2009. Multiple personalities of Streptomyces spp. from the rhizosphere of apple cultivated in brassica seed meal amended soils. Phytopathology 99:S150.
• Mazzola, M., Brown, J., Zhao, X., Izzo, A. D., and Fazio, G. 2009. Interaction of brassicaceous seed meal and apple rootstock on recovery of Pythium spp. and Pratylenchus penetrans from roots grown in replant soils. Plant Dis. 93:51-57.