Selection in heterogeneous soybean populations: 3. Identification of valuable genotypes

Identification of valuable genotypes in hybrid populations within the theory of environmental markers (‘background traits’) involves elimination of phenotypic variation components that are useless for breeder by means of introducing environmental adjustment. Lack of satisfactory environmental markers for selection in MG 000-00 of soybean populations requires designing of environmental indices. A new index based on ratio of plant biomass to stem length displayed high environmental correlation with plant seed yield (0.94-0.99) and eliminated about 90% of ecological competitive variance. However, it tended to underestimate seed yield of weak competitors thus distorting selection results in dry years. Therefore, a double-step adjustment procedure to estimate genetically useful individual plant seed yield is proposed. At the 1st stage, genotypic competitive ability is adjusted according to its linear regression on total node number. At the 2nd stage, adjustment by the proposed environmental index is introduced. The described procedure was applied to model soybean populations simulating hybrid populations. This allowed increasing the best genotype frequency in the selected subpopulation from 18 to 55% (4-year average). Selection efficacy was stable and did not depend on environmental index, rainfall distribution and competitive ability of the genotypes included into the model populations.