VIEW ARTICLE

The Effects of Root Knot Nematodes on Bacterial Wilt in Alfalfa. O. J. Hunt, Research Agronomist, ARS, USDA, Reno, Nevada 89507; G. D. Griffin(2), J. J. Murray(3), M. W. Pedersen(4), and R. N. Peaden(5). (2)Research Nematologist, ARS, USDA, Logan, Utah 84321, (3)Research Assistant, U.S. Pasture Research Lab., State College, Pennsylvania 16802, (4)Research Agronomist, ARS, USDA, Logan, Utah 84321; (5)Research Agronomist, ARS, USDA, Reno, Nevada 89507. Phytopathology 61:256-259. Accepted for publication 8 September 1970. DOI: 10.1094/Phyto-61-256.

Meloidogyne hapla in association with Corynebacterium insidiosum increased the incidence of bacterial wilt disease in alfalfa Medicago sativa in studies at Logan, Utah, and Reno, Nevada. The incidence of bacterial wilt symptoms in Moapa and Ranger alfalfa plants infected with M. hapla approached the incidence in plants where the rootball was cut before inoculating with C. insidiosum. The cultivars DuPuits and Lahontan showed 90 and 42% C. insidiosum infection, respectively, where M. hapla and C. insidiosum were in association in uncut roots at Logan, Utah. Corynebacterium insidiosum alone on uncut roots resulted in bacterial wilt symptoms in only 14 and 5% of the plants in the two cultivars. Studies at Reno, Nevada, in which seedlings of the cultivars DuPuits were inoculated with M. hapla and C. insidiosum alone and in combination, then transferred to individual pots at 28, 44, and 65 days after emergence, showed no visible symptoms of bacterial wilt after 4 months with C. insidiosum alone and the untreated check. Meloidogyne hapla and C. insidiosum in combination caused bacterial wilt symptoms in 32, 25, and 56% of treated plants transferred to individual pots 28, 44, and 65 days after inoculation, and 57% in those continuously grown in initial pots. Corynebacterium insidiosum was present in plants inoculated with pure cultures of the organism alone. These studies indicate a close relationship between the incidence of bacterial wilt disease and presence of M. hapla in the plants. They also indicate that M. hapla may be hastening the colonization of alfalfa plants by C. insidiosum.