A unique strategy to improve the floral traits and seed yield of Brassica oleracea cytoplasmic male sterile lines through honey bee-mediated selection

Abstract

Improvement in flower structure and seed yield is one of the main objectives when developing cytoplasmic male sterile lines (CMS) in vegetable Brassicas for their successful use in the development of F1 hybrids. However, it is found that the introgression of alien cytoplasm alters the reproductive structure of Brassica oleracea genotypes and the altered floral structure in these lines can be improved only marginally even after several generations of manual selection. We have tested an alternative selection strategy using honey bee (Apis cerena indica) as the selection agent in five selection cycles in three CMS lines of cauliflower (Ogu1A, Ogu2A and Ogu3A). Selected plants with the highest seed yield, determined through honey bee selection, were bulked to raise the plants for next generation. The reproductive structures of the CMS plants improved significantly after five cycles of honey bee-mediated selection. Seed yield/plant, nectar quantity, size of nectary and flower size improved significantly in all three CMS lines at the end of the selection cycles. Quantity of nectar increased from 0.45 to 1.45 µl and from 0.37 to 1.49 µl per flower in CMS lines Ogu1A and Ogu3A, respectively, after five cycles of selection; similarly, quantity of seeds per plant improved from 13.48 to 20.71 g and from 12.77 to 17.57 g in the same CMS lines, respectively. The extent of improvement in nectar quantity and seed yield was comparatively lower in CMS line Ogu2A. The occurrence of different floral deformities was also reduced in all three CMS lines after five cycles of honey bee-mediated selection. CMS lines Ogu1A and Ogu3A responded better to honey bee-mediated selection than did CMS line Ogu2A. This novel strategy of honey bee-mediated selection can be used to develop CMS lines with higher seed yield in different crops where cytoplasmic male sterility is commercially used in hybrid seed production.