Molecular mapping and inheritance of restoration of fertility (Rf) in A4 hybrid system in pigeonpea (Cajanus cajan (L.) Millsp.)

Commercial hybrids in pigeonpea are based on A4 cytoplasmic male sterility (CMS) system, and their fertility restoration is one of the key prerequisites for breeding. In this context, an effort has been made to understand the genetics and identify quantitative trait loci (QTL) associated with restoration of fertility (Rf). One F2 population was developed by crossing CMS line (ICPA 2039) with fertility restorer line (ICPL 87119). Genetic analysis has shown involvement of two dominant genes in regulation of restoration of fertility. In parallel, the genotyping-by-sequencing (GBS) approach has generated ~ 33 Gb data on the F2 population. GBS data have provided 2457 single nucleotide polymorphism (SNPs) segregating across the mapping population. Based on these genotyping data, a genetic map has been developed with 306 SNPs covering a total length 981.9 cM. Further QTL analysis has provided the region flanked by S8_7664779 and S8_6474381 on CcLG08 harboured major QTL explained up to 28.5% phenotypic variation. Subsequently, sequence information within the major QTLs was compared between the maintainer and the restorer lines. From this sequence information, we have developed two PCR-based markers for identification of restorer lines from non-restorer lines and validated them on parental lines of hybrids as well as on another F2 mapping population. The results obtained in this study are expected to enhance the efficiency of selection for the identification of restorer lines in hybrid breeding and may reduce traditional time-consuming phenotyping activities

Molecular mapping and inheritance of restoration of fertility (Rf) in A4 hybrid system in pigeonpea (Cajanus cajan (L.) Millsp.)

Commercial hybrids in pigeonpea are based on A4 cytoplasmic male sterility (CMS) system, and their fertility restoration is one of the key prerequisites for breeding. In this context, an effort has been made to understand the genetics and identify quantitative trait loci (QTL) associated with restoration of fertility (Rf). One F2 population was developed by crossing CMS line (ICPA 2039) with fertility restorer line (ICPL 87119). Genetic analysis has shown involvement of two dominant genes in regulation of restoration of fertility. In parallel, the genotyping-by-sequencing (GBS) approach has generated ~ 33 Gb data on the F2 population. GBS data have provided 2457 single nucleotide polymorphism (SNPs) segregating across the mapping population. Based on these genotyping data, a genetic map has been developed with 306 SNPs covering a total length 981.9 cM. Further QTL analysis has provided the region flanked by S8_7664779 and S8_6474381 on CcLG08 harboured major QTL explained up to 28.5% phenotypic variation. Subsequently, sequence information within the major QTLs was compared between the maintainer and the restorer lines. From this sequence information, we have developed two PCR-based markers for identification of restorer lines from non-restorer lines and validated them on parental lines of hybrids as well as on another F2 mapping population. The results obtained in this study are expected to enhance the efficiency of selection for the identification of restorer lines in hybrid breeding and may reduce traditional time-consuming phenotyping activities

Towards defining heterotic pools for accelerating hybrid breeding in pigeonpea

Recently released pigeonpea hybrids for cultivation in farmers’ fields have shown their potential to elevate the yield levels. For instance, the world’s first grain legume hybrid of pigeonpea ICPH 2671 showed 47% yield advantage over the check varieties. Generally, the development of such hybrids is based on selection efficiency of breeding program; breeders make thousands of random crosses between cytoplasmic male sterile (CMS) lines and tester lines. In order to enhance the selection efficiency, genomic diversity along with the phenotyping data have been used for predicting the best possible parental combinations. This approach has been successfully used in defining heterotic pools in many crop species such as maize, rice, sunflower, and rapeseeds.. With an aim to define heterotic pools in pigeonpea, a set of 104 parental lines (09 CMS, 13 maintainers and 82 restorers) have been re-sequenced following whole genome re-sequencing (WGRS) approach. WGRS yielded a total of 511 GB data with the coverage ranging from 5X to 10X. A total of 3.4 million SNPs have been identified across parental lines. Structural variations such as copy number and presence/ absence variations have been also identified. In parallel, these parental lines have been used to develop test crosses in factorial mating design. F1 hybrids along with parental lines were phenotyped for yield and yield related traits at two locations in India, namely ICRISAT, Telangana State and ARS-Gulbarga, Karnataka. The availability of genome-wide SNP variations combined with the phenotypic data will be used for deploying genomic selection to define hetereotic pools in pigeonpea for accelerating hybrid breeding program