Submitted to: Phytopathology
Publication Type: Proceedings
Publication Acceptance Date: 3/1/2005
Publication Date: 6/1/2005
Citation: Cohen, M.F., Brown, J., Mazzola, M. 2005. Infectivity of pythium toward apple seedlings in soil amended with low-glucosinolate brassica napus seed meal. Phytopathology 95:S20.
Technical Abstract: Incorporation of Brassica napus (rape)seed meal (RSM) into orchard soils is effective in preventing replant disease of apple. However, utilization of a low glucosinolate content RSM can increase the incidence of root infection by Pythium spp. Application of mefenoxam at the time of RSM incorporation can control Pythium but the development of resistance and negative impacts on non-target organisms, such as protozoa, do not make this a sustainable solution. Pythium root infection was greatest when apple seedlings were planted immediately following incorporation of low-glucosionate B. napus var. Athena RSM, especially if the meal was in a flaked rather than powdered form. Seedlings planted three weeks following amendment exhibited reduced Pythium infection rates even though the numbers of culturable Pythium in the soil had increased from the first week. Amended soils showed rapid declines in cis-oleic acid, a suitable energy source for many microorganisms, concomitant with increases in the numbers of bacteria and proportion of bacterial fatty acid markers in the soil, indicated both catabolism and transformation of RSM components into bacterial biomass. Declines in the infectivity of Pythium over time may be due to the loss of carbon substrate combined with increased competition.