ABSTRACT
MAIN CONCLUSION: 'Petaloid' cytoplasmic male sterility is commonly used as a stable genetic mechanism in carrot hybrid breeding. Its introgression in tropical carrot showed morphometric changes and molecular markers were identified for detection at early stage. Cytoplasmic male sterility (CMS) is the only genetic mechanism in carrot for commercial exploitation of heterosis and production of low cost affordable hybrid seeds. The 'petaloid' CMS system is stable and commonly used in hybrid breeding in temperate carrot but there is no information available on existence of natural CMS system in tropical Asiatic carrot. Therefore, the present study was aimed to investigate morphometric traits and organizational features of cytoplasmic atp9 gene sequences in newly converted CMS lines (BC4-7) of tropical carrot. The CMS lines had root traits at par with fertile counterparts while floral traits had variation. Petal colour and length, petaloids colour and shape and style length showed differences among the CMS lines and with their maintainers. Molecular markers are effective to establish male sterility at genetic level, for this, six fixed and stable CMS lines were screened with seven novel primer combinations. Out of which five pairs produced clearly distinguishable bands in CMS lines and their fertile counterparts. The study confirmed that the region between 3' end of atp9-1/atp9-3 gene and 5' end of region of homology to Arabidopsis thaliana mtDNA is ideal for developing the trait specific markers. These new CMS lines have potential to use in hybrid development and molecular markers will be useful to confirm male sterility to rogue out fertile plants.
