Identification of sources of resistance to four species of root-knot nematodes in tobacco

Resistance to the southern root-knot nematode, Meloidogyne incognita races 1 and 3, has been identified, incorporated, and deployed into commercial cu ltivars of tobacco, Nicotiana tabacum. Cultivars with resistance to other e conomically important root-knot nematode species attacking tobacco, M. aren aria, M. hapla, M. javanica, and other host-specific races of M. incognita, are not available in the United States. Twenty-eight tobacco genotypes of diverse origin and two standard cultivars, NC 2326 (susceptible) and Speigh t G 28 (resistant to M. incognita races 1 and 3), were screened For resista nce to eight root-knot nematode populations of North Carolina origin. Based on root gall indices at 8 to 12 weeks after inoculation, all genotypes exc ept NC 2326 and Okinawa were resistant to M. arenaria race 1, and races 1 a nd 3 of M. incognita. Except for slight root galling, genotypes resistant t o M. arenaria race 1 responded similarly to races 1 and 3 of M. incognita. All genotypes except NC 2356, Okinawa, and Speight G 28 showed resistance t o M. javanica. Okinawa, while supporting lower reproduction of M. javanica than NC 2326, was rated as moderately susceptible. Tobacco breeding lines 8 1-R-617A, 81-RL-2K, SA 1213, SA 1214, SA 1223, and SA 1224 were resistant t o M. arenaria race 2, and thus may be used as sources of resistance to this pathogen. No resistance to M. hapla and only moderate resistance to races 2 and 4 of M. incognita were found in any of the tobacco genotypes. Under n atural field infestations of M. arenaria race 2, nematode development on re sistant tobacco breeding lines 81-RL-2K SA 1214, and SA 1215 was similar to a susceptible cultivar dth some nematicide treatments; however, quantity a nd duality of yield were inferior compared to K 326 plus nematicides.