Identification of the Chromosome Carrying the Factor for Resistance to Meloidogyne incognita in Tobacco
To identify the chromosome carrying the factor for resistance to Meloidogyne incognita in tobacco, crosses were made between resistant tobacco 'NC95' as pollen parent and each of the 12 tobacco monosomics (A-L) representative of the Tomentosae half of the Nicotiana tabacum chromosome complement. Of the F[sub1] seedlings, 927 plants were grown for observation. From these, 223 plants were selected as possible monosomics on the basis of morphological characteristics. These plants were self-pollinated, and the resulting F[sub2] plants were inoculated with both M. incognita acrita and M. incognita incognita. Sixteen F[sub2] populations, derived from the haplo-G monosome, were completely resistant. All of the F[sub2] populations derived from the other 11 monosomic crosses segregated into a 3:1 (resistant:susceptible) ratio. These results indicate that the factor for resistance to M. incognita is located on the G chromosome of N. tabacum. This is the first report establishing the N. tabacum chromosome that carries the factor for root-knot resistance. The results are consistant with our earlier evidence that M. incognita resistance in tobacco is derived from N. tomentosa, a species in the section Tomentosae of the subgenus Tabacum, genus Nicotiana. The other 12 chromosomes of N. tabacum have affinities with N. sylvestris, section Alatae, subgenus Petunoides, genus Nicotiana. Key words: genetics, Meloidogyne incognita, resistance, monosomic analysis, Nicotiana tabacum.