Population dynamics in introgression of wild male sterile cytoplasm into Brassica oleracea: a small population based breeding modelr

Cytoplasmic male sterile (CMS) lines are used widely in vegetable brassicas to develop F1 hybrids. However, the population dynamics in introgression of male sterile cytoplasm into the nuclear background of B. oleracea is not understood. We have tested 3 models of back crossing using different number of plants for last 12 years. A back cross introgression model using single plant for initial 3 generations and 6 plants thereafter till BC9 was most effective in ensuring uniformity and complete recovery of recurrent parent nuclear genome. The agronomic and floral performance was tested at different stages of back crossing. Inbreeding depression for various traits was highest when single plant was used till BC9 followed by 6 plants from BC4 onwards. Lowest inbreeding depression was recorded in the backcross model based on 12 lants from BC4 onwards. However, when 12 plants were selected from BC4 onwards, there was significant difference among A and B lines for various agronomic traits at BC9 stage. Hybrids were produced using these CMS lines after 2 generation of bulking. Performances of hybrids were at par for the CMS lines developed using 6 plants and 12 plants from BC4 onwards. However, the population developed through single plant selection till BC9 lost its vigor completely and was not able to recover the original characteristics even after 2 generation of bulking. For the first time we report a small population based model for introgression of desirable traits into B. oleracea nuclear background. This model will be immensely useful in introgression of desirable traits in brassica vegetables through backcrossing because of its practical application.