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Response of Root-Knot Resistant Tobacco to Concomitant Populations of Meloidogyne Species. TensonB S. Ng'ambi, Graduate Research Assistant, North Carolina State University, Raleigh 27695-7620. Rebeca C. Rufty, Associate Professor, Department of Crop Science, North Carolina State University, Raleigh 27695-7620; and Kenneth R. Barker, Professor, Depart-ment of Plant Pathology, North Carolina State University, Raleigh 27695-7616. Plant Dis. 79:1008-1013. Accepted for publication 20 May 1995. Copyright 1995 The American Phytopalhological Society. DOI: 10.1094/PD-79-1008.

Mixed populations of Meloidogyne species commonly occur in most flue-cured tobacco (Nicotiana tabacum L.) fields in the southeastern United States. The interaction of Meloi-dogyne arenaria race 2 (Ma) and M. incognita race 3 (Mi) on the Mi-resistant flue-cured to-bacco cv. Speight G-28 and on a root-knot susceptible flue-cured tobacco cv. NC 2326 (control) was evaluated under greenhouse conditions. Plants of both cultivars were inoculated with 1,500 or 3,000 eggs of Ma or Mi alone, or with a combination of 1,500 eggs of each spe-cies. Root penetration (number of juveniles per g of root) with the mixed population assessed 10 days after inoculation (DAI) was comparable to that of Ma alone on the Mi-resistant to-bacco cultivar, and of either nematode species alone on the susceptible cultivar. Also, nematode population density (number of nematodes per g of root, all stages except eggs), numbers of mature females per g of root, root damage (percent root area galled), and nematode reproduc-tion (number of eggs per g of root) on Speight G-28 30 and/or 48 DAI with mixed population were not greater than those attributable to Ma alone. Indeed, inoculation with the mixed popu-lation resulted in slightly lower nematode population density (except at 48 DAI), root damage, and nematode reproduction on Mi-resistant cultivar than with Ma alone at the 1,500 egg inocu-lum level. The concomitant inoculation of Ma and Mi on NC 2326 did not differ from single inoculation with Ma for all variables measured, except reproduction at 48 DAI. These data in-dicate that Speight G-28 resistance to Mi was not reduced with concomitant infections of Ma and Mi. Fewer Mi than Ma mature females were recovered from the susceptible cultivar in the mixed population, indicating that Ma was more competitive than Mi.