Suppression of specific apple root pathogens by Brassica napus seed meal amendment regardless of glucosinolate content

The impact of Brassica napus seed meal on the microbial complex that incite s apple replant disease was evaluated in greenhouse trials. Regardless of g lucosinolate content, seed meal amendment at a rate of 0.1% (vol/vol) signi ficantly enhanced growth of apple and suppressed apple root infection by Rh izoctonia spp. and Pratylenchus penetrans. High glucosinolate B. napus cv. Dwarf Essex seed meal amendments did not consistently suppress soil populat ions of Pythium spp. or apple root infection by this pathogen. Application of a low glucosinolate containing B. napus seed meal ar a rare of 1.0% (vol /vol) resulted in a significant increase in recovery of Pythium spp. from a pple roots, and a corresponding reduction in apple seedling root biomass. W hen applied at lower rates, B. napus seed meal amendments enhanced populati ons of fluorescent Pseudomonas spp., but these bacteria were not recovered from soils amended with seed meal at a rate of 2% (vol/vol). Seed meal amen dments resulted in increased soil populations of total bacteria and actinom ycetes. B. napus cv. Dwarf Essex seed meal amendments were phytotoxic to ap ple when applied at a rate of 2% (vol/vol), and phytotoxicity was not dimin ished when planting was delayed for as long as 12 weeks after application. These findings suggest that B. napus seed meal amendments can be a useful t ool in the management of apple replant disease and, in the case of Rhizocto nia spp., that disease control operates through mechanisms other than produ ction of glucosinolate hydrolysis products.