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Interaction of Meloidogyne hapla and Fusarium oxysporum f. sp. medicaginis on Alfalfa. G. D. Griffin, Nematologist, USDA-ARS, Forage and Range Research Laboratory, Utah State University, Logan 84322-6300; B. D. Thyr, Former plant pathologist, USDA-ARS, University of Nevada, Reno 89503. Phytopathology 78:421-425. Accepted for publication 6 October 1987. This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological Society, 1988. DOI: 10.1094/Phyto-78-421.

The incidence of fungal infection and vascular discoloration from a single inoculation with Fusarium oxysporum f. sp. medicaginis was similar in Ranger alfalfa, susceptible to both Meloidogyne hapla and F. o. f. sp. medicaginis, and Nevada Synthetic XX alfalfa, resistant to M. hapla and susceptible to F. o. f. sp. medicaginis; less fungal infection and vascular discoloration occurred in Moapa 69 alfalfa, susceptible to M. hapla and resistant to F. o. f. sp. medicaginis. Fungal infection and root discoloration increased (P< 0.05) and plant growth decreased (P< 0.01) in Ranger and Moapa 69 at 2030 C when inoculation with M. hapla preceded inoculation with F. o. f. sp. medicaginis by 28 days. Plant mortality in Ranger and Moapa 69 also increased (P< 0.05) following sequential inoculations with the two organisms and was greatest at 25 C. In Nevada Synthetic XX, the incidence of fungal infection and root discoloration from combined inoculations (compared to the effects of a single inoculation with the fungus) increased (P< 0.05) only at 30 C, where resistance to M. hapla is lost. Combined inoculations suppressed the incidence of root-knot galling (P< 0.05) and nematode reproduction (P< 0.05) on both Ranger and Moapa 69, but not on Nevada Synthetic XX. Single inoculations with M. hapla reduced (P< 0.05) the growth of Ranger and Moapa 69 at 25 and 30 C and Nevada Synthetic XX at 30 C.

Additional keywords: additive, galling indices, Medicago sativa, northern root-knot nematode.