Response to root-knot resistant tobacco to concomitant populations of Meloidogyne species

Mixed populations of Meloidogyne species commonly occur in most flue-cured tobacco (Nicotiana tabacum L.) fields in the southeastern United States. The interaction of Meloidogyne arenaria race 2 (Ma) and M. incognita race 3 (Mi) on the Mi-resistant flue-cured tobacco 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 species. 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 tobacco 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 reproduction (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 population 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 inoculum 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 indicate 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.