2011 Annual Report 1a.Objectives (from AD-416) This research program seeks to identify and implement methods, which are compatible with organic production systems, for the control of disease phenomena that are biologically complex. Our goal is to develop a management program that ensures successful establishment of new fruit trees on old orchard sites and sustains productivity of these orchards through maximizing the efficiency of the biological resources resident to the orchard soil ecosystem. 1b.Approach (from AD-416) A composite brassicaceous seed meal in concert with use of a disease tolerant apple rootstock will be evaluated as an alternative to soil fumigation for control of apple replant disease in field trials. The impact of seed meal particle size on generation of biologically active chemistries (allyl-isothiocyanate) from Brassica juncea seed meal soil amendment, and composition of the resident soil microbial community contributing to disease suppression. The effect of different brassicaceae seed meals or composite seed meal amendments on composition and activity of resident soil fauna communities involved in N mineralization will be determined. The use of a composite seed meal to decrease rates nitrification and thus minimize N loss resulting from leaching will be assessed. D 3.Progress Report This project relates to objective 1 of the associated in-house project, which seeks to determine the relative contribution of chemistry and soil biology to the control of soil borne diseases that is realized through soil incorporation of mustard (Brassica juncea) plant residues. During FY2011 examination of the effect of brassicaceae seed meals on the long-term suppression of the soilborne pathogen Pythium abappressorium was continued. Results indicated that long-term control of Pythium in apple orchard soils obtained in response to Brassica juncea seed meal amendment resulted from specific changes in soil biology, and the active entity was likely a component of the soil fungal community. However, changes in the fungal community which were required to obtain disease control, were dependent upon generation of allyl isothiocyanate, a product that is produced in response to hydrolysis of the dominant glucosinolate contained in B. juncea seed meal. Production of allyl isothiocyanate in orchard soil resulted in a fungal community that was dominated by Trichoderma spp., an organism that is known to parasitize Pythium. Our results indicated that active management of resident soil biology through selection of an appropriate brassicaceae seed meal amendment can generate a biologically suppressive soil providing long-term control of root diseases caused by Pythium spp. Activity and progress were monitored through an annual report submitted to the USDA-CSREES.