Novel CMS lines in pigeonpea [Cajanus cajan（L.）Millspaugh] derived from cytoplasmic substitutions,and their effective restoration and deployment in hybrid breeding

The availability of stable cytoplasmic male sterile（CMS or A） lines coupled with a robust restoration system（R lines） is an essential prerequisite for efficient hybrid breeding.CMS-enabled hybrid technology holds immense potential to enhance the long-stagnant productivity of pigeonpea. In the present investigation, cytoplasmic substitutions were made in the nuclear backgrounds of early-maturing pigeonpea varieties or lines. Three new CMS lines（ICPL 88039 A, Pusa 992 A, and DPP 3-2A） resulted from genetic crosses involving cytoplasmic donors from A2（GT 288A） and A4（ICPA 2089） categories. In addition to visual inspection of anthers, pollen-staining techniques and scanning electron microscopy（SEM）analysis were used to confirm pollen sterility. Further, given the relevance of the plant mitochondrial genome to CMS manifestation, 25 mitochondrion-specific DNA markers were assayed on these newly developed A lines and isogenic maintainer（B） lines. DNA polymorphism between Pusa 992 A and Pusa 992 B as revealed by the nad7a_del marker confirmed the successful combination of sterilizing cytoplasm（A4） and nonrestoring nuclear background（Pusa 992）. Such cytoplasm-specific DNA markers are required for A2-CMS as well. Further, to assess restoration ability, potential restorers were crossed with these CMS lines, and as a consequence, promising A × R combinations exhibiting 100%pollen fertility could be identified. In parallel, we also analyzed the inheritance patterns underlying fertility restoration using ICPL 88039A-derived F2 and BC1F1populations,and established a monogenic dominant model to explain the phenomenon of A2-CMS restoration. In summary, we report the successful development of new CMS lines and describe their effective deployment in hybrid breeding of pigeonpea.