Institute of Genetics, Acad. Sci. 1 Chisinau, Moldova Republic

Background and objectives
In the Moldova Republic, as well as in other regions of the world, rot of roots, stems, and seeds induced by the fungus genus Fusarium is responsible for great losses in yields of soybean. The study of the genetic mechanisms ensuring soybean resistance to diseases should contribute to the reduction of losses.

Materials and methods
Fusarium resistance was evaluated in F1, F2 and backcross generations of 10 hybrid populations. Sensitivity to soybean seedling blight was evaluated at the plantlet stage. The heritability was calculated according to Allard and Simmonds and the degree of dominance according to the method of Allard. The total contribution of the additive and dominance effects, as well as epistasis in the gene expression of soybean resistance to seedling blight, was determined.

Results and conclusion
Reaction of the hybrids originating from the cultivars differing in resistance showed that in major cases and especially in the combination MRxR and RxR, the F1 genotypes manifested enhanced resistance, while genotypes possessing a partial resistance predominated in F2. The genes showed partial to almost complete dominant inheritance. Heritability of soybean resistance to Fusarium in the F2 averaged 0.7.

Analysing the absolute values and t-test data of the genetic factors involved in the control of the heritability of soybean resistance to Fusarium showed that dominance gene action was the most important factor in the inheritance of resistance. Epistatic effects occurred at a lower frequency. The number of effective factors (genes) was estimated between one or two to five or more for various cultivars.

Taking into consideration the fact that the predominance of dominance effects contributes to early expression of resistance genes, it is concluded that soybean seedling blight resistant genotypes may be selected in early generations.