Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/26/2010
Publication Date: 6/1/2010
Citation: Mazzola, M., Brown, J. 2010. Efficacy of brassicaceous seed meal formulations for the control of apple replant disease in conventional and organic production systems. Plant Disease. 94:835-842. Interpretive Summary: Organic soil amendments often have been promoted as a means to control soilborne plant diseases. However, the effective use of such an environmentally sensitive method of disease control has been impeded by a lack of understanding concerning the means by which amendments provide disease control. Tissues from plants belonging to the Brassicaceae have been promoted as a soil amendment for the control of soilborne plant diseases due to their production of glucosinolates, which yield anti-microbial compounds upon hydrolysis. In this study, various brassicaceae seed meals were found to require an active soil microbial community to provide long term control of the fungal pathogen Rhizoctonia solani. However, in the case of Brassica juncea seed meal, initial disease control corresponded with the release of glucosinolate hydrolysis products. B. juncea seed meal was also superior to Brassica napus or Sinapis alba seed meals for the control of root infection by Pythium spp. and long term suppression of the plant parasitic nematode Pratylenchus pentrans. B. juncea seed meal amendment was not suitable as a standalone treatment in the field as it promoted infection of apple roots by the pathogen Phytophthora cambivora. When used in concert with a post plant application of mefenoxam, B. juncea seed meal amendment was as effective as soil fumigation for control of apple replant disease. A composite amendment containing seed meal of B. napus and B. juncea may be a superior product for control of apple replant disease in organic production systems as this mixture appears capable of controlling all components of the causal microbial complex.
Technical Abstract: Brassica tissues are often promoted as a soil amendment for control of soilborne plant diseases due to their production of glucosinolates, which yield anti-microbial compounds upon hydrolysis. Studies demonstrated that mechanisms operating in the control of Rhizoctonia root rot of apple in response to Brassicaceae seed meal amendments varied in both a species and temporal manner. Seed meal of Brassica juncea, B. napus and Sinapis alba all required an active soil microbial community for the optimal induction of disease control. However, no one of the tested seed meals could provide comprehensive control of the pathogen complex that incites apple replant disease. In conventional production systems, a post-plant application of mefenoxam in concert with pre-plant application of B. juncea seed meal amendment was as effective as soil fumigation for the control of replant disease and enhancing tree growth and yield. For organic systems, a composite seed meal formulation was devised. When applied in a composite amendment, B. juncea seed meal abolished the B. napus-induced proliferation of resident Pythium spp. populations. The composite seed meal was as effective as Telone-C17 soil fumigation for the suppression of lesion nematode populations. In field trials, growth of Gala/M26 apple in soils treated with the composite seed meal formulation was equivalent to that attained in fumigated soils and significantly greater than the no treatment control.