The analysis of a full diallel cross of ten tobacco varieties showed that genetic control of resistance to root-knot nematodes (Meloidogyne incognita) in tobacco was governed by partial dominance. When measuring the overall genetic variance, the portion of additive variance was found to be very substantial. This property may well be inherited by progenies and with a high degree of heritability (0.60-0.63). Partitioning the total sums of squares of the genotypes into the sum of squares for general (GCA) and specific combining ability (SCA) of parents and hybrids points to additive and non-additive gene activities in generating resistance to root-knot nematodes in tobacco. Because of significant reciprocal differences, the maternal cytoplasm plays an important role in the inheritance of resistance to root-knot nematodes. The proportion of additive and heritable variance was significant and to such an extent (60 %) that a selection for resistant lines might be a promising project. Since some varieties show a high GCA for resistance, they could be regarded as donors for resistance for progenies. In addition, the significantly high SCA and resistance of several hybrids would suggest successful selection of lines with resistance to root-knot nematodes in tobacco.
