Development and utilization of an efficient cytoplasmic male sterile system for Cai-xin (Brassica rapa L.)

• An efficient cytoplasmic male sterile (CMS) line of Brassica vegetable Cai-xin (Brassica rapa L. ssp. chinensis var. utilis Tsen et Lee) were newly developed by backcrossing of six local inbred lines with a new eru CMS line of vegetable purple cai-tai (Brassica rapa L. var. purpurea Bailey) from South China.
• Through research, six newly developed Cai-xin eru CMS lines were evaluated and characterized for morphology, cytology and their heterosis utilization, this would broaden the CMS germplasm resources in Cai-xin.
• Heterosis analysis indicated that the six newly dereived eru CMS lines of Cai-xin provided a novel CMS system for breeding and heterosis utilization in Cai-xin.

Six cytoplasmic male sterile (CMS) lines of Brassica vegetable Cai-xin (Brassica rapa L. ssp. chinensis var. utilis Tsen et Lee) were newly developed by backcrossing of six local inbred lines with a new eru CMS line of the vegetable purple cai-tai (B. rapa L. var. purpurea Bailey) from South China. The sterility of these Cai-xin eru CMS lines was stable and complete. The line 4A represented typical sterility and produced six off-white and shriveled stamens without pollen grains in the anthers. Paraffin sectioning comparison of the anthers between the CMS line 4A and its maintainer line 4B showed that their developmental differentiations started at the early to middle mononucleate microspore stage. The tapetum in the CMS line 4A was vacuolized highly and expanded radically, which extruded the developing microspores and caused their adhesion with each other and failure to develope mature pollen. With six CMS lines as female parents and 6 fertile lines as pollen parents, 36 hybrids were produced and their potentials of heterosis were analyzed. In general, mid-parent heterosis was detected for most of the 14 agronomic, yield and quality traits, such as petiole length (19.01%), weight of main flower stalk (35.96%), and soluble protein content (1.20%). These results indicated that the six newly derived eru CMS lines of Cai-xin provided a novel CMS system for its breeding and heterosis utilization.