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 88039A, Pusa 992A, 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 992A and Pusa 992B 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 BC1F1 populations, 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.