Development of Ogura CMS restorers in Brassica oleracea subspecies via direct RfoB gene transformation.

KEY MESSAGE: The Ogura CMS RfoB restorer developing via RfoB gene transformation was utilized to produce specific morphological Ogura CMS restorers and clubroot resistance lines in Brassica oleracea subspecies. Brassica oleracea vegetables including cabbage, cauliflower, kohlrabi, Brussels sprouts and Chinese kale are morphologically very different despite being members of the same species. The Ogura cytoplasmic male sterility (CMS) system is the most stable strategy for the hybrid breeding of these species. However, this limits the utilization of some excellent genes due to the lack of fertile restorer genes in the system. Herein, to efficaciously use Ogura CMS, the Ogura CMS RfoB restorer was produced by transforming the modified RfoB restorer gene into the Ogura CMS line 'CMS2016' of B. oleracea var. capitata. This gene was shown to recover fertility of natural Ogura CMS lines in B. oleracea subspecies and create transient Ogura CMS RfoB restorers such as the clubroot resistance Ogura CMS RfoB restorer. Interestingly, clubroot resistant individuals without transgenic elements were screened in the progenies of hybrids between B. oleracea inbred lines and the clubroot resistance Ogura CMS RfoB restorer. In addition, 18 different morphological Ogura CMS restorers were developed to specifically recover fertile of Ogura CMS cultivars in B. oleracea subspecies.