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Effects of Rhizobia, Metalaxyl, and VA Mycorrhizal Fungi on Growth, Nitrogen Fixation, and Development of Pythium Root Rot of Sainfoin. S. F. Hwang, Biological Sciences, Alberta Environmental Centre, Vegreville, AB, Canada T9C 1T4. P. Chakravarty, and D. Prévost. Forestry Canada, Northern Forestry Centre, 5320–122 St., Edmonton, AB T6H 3S5; and Research Station, Agriculture Canada, Sainte-Foy, PQ G1V 2J3. Plant Dis. 77:1093-1098. Accepted for publication 1 August 1993. Copyright 1993 The American Phytopathological Society. DOI: 10.1094/PD-77-1093.

The potential for Pythium species to reduce sainfoin (Onobrychis viciifolia) seedling growth and for rhizobia and vesicular-arbuscular (VA) mycorrhizal fungi to enhance seedling growth were studied under controlled conditions. Seedling emergence and shoot dry weights of cvs. Nova and Melrose in pasteurized soils infested with each of 18 isolates of Pythium spp. were reduced. Seedlings inoculated with arctic rhizobia grew more rapidly than noninoculated seedlings. Plant growth, nodule dry weight, nitrogenase activity, and mycorrhizal colonization of sainfoin dually inoculated with Rhizobium plus either Glomus fasciculatus or G. intraradices were greater than those of uninoculated plants or those inoculated with either rhizobia or mycorrhizal fungus alone; nitrogen content was higher in plants concomitantly inoculated with Rhizobium plus G. intraradices. Seedling survival and growth in Pythium-infested soil increased for seeds treated with metalaxyl. Interactions of VA mycorrhizal fungi and two isolates of Pythium were investigated under controlled conditions. Shoot dry weights of sainfoin plants inoculated with VA mycorrhizal fungi significantly exceeded those of nonmycorrhizal plants. Seedlings inoculated with VA mycorrhizal fungi had a lower incidence of root rot than nonmycorrhizal ones. This study suggested that a combination of rhizobia, metalaxyl, and VA mycorrhizal fungi could be used to improve the establishment and vigor of sainfoin in Pythium-infested soils.

Keyword(s): fungicide.