Elucidating mitochondrial DNA-markers of Ogura-based CMS linesin Indian cauliflowers (Brassica oleracea var. botrytis L.) and their floral abnormalities due to diversity in cyto-nuclear interaction

Abstract

Background: Mitochondrial markers can be used to differentiate diverse mitotypes as well as cytoplasms in angiosperms. In cauliflower, cultivation of hybrids is pivotal in remunerative agriculture and cytoplasmic male sterile lines constitute an important component of the hybrid breeding. Thus, the breeders look for utilizing diverse male sterile cytoplasms in hybrid progamme. In diversifying source of male sterility,it is essential to appropriately differentiate among the available male sterile cytoplasms in cauliflower.PCR polymorphism atthe key mitochondrial genes associated with male sterility will be useful in developing mitochondria specific markers for the different male sterile cytoplasms. Also, the auto and alloplasmic cytonuclear combinations result in complex floral abnormalities.Thus, the study aimed at developing mitotype specific markers of the sterile cytoplasms and to unravel thegenetic effects of the cytonuclear interactions on flower morphology in Indian cauliflowers.Results: In PCR based analysis using a set of primers targeted to orf-138, 76 Indian cauliflower lines showed presence of Ogura cytoplasm though amplicons showed polymorphism within the ofr-138 sequence. The polymorphic loci were found to be spanning over 200-280 bp and 410-470bp genomic regions of BnTR4 and orf125, respectively. Sequence analysis revealed that such cytoplasmic genetic variations could be due to single nucleotide polymorphisms and insertion or deletions of31/51 nucleotides.The cytoplasmic effects on varying nuclear-genetic backgrounds led to varying degree of floral malformations ranging from reduction in flower size, stamens and style length, modification in position of styleand anthers, absence of non-functional stamens to other floral abnormalities. These floral malformations caused dysplasia of flower structure affecting female fertility and inefficient nectar production.Conclusions: The mitochondria specific markers can distinguish ogurabased male sterile cytoplasm. Large number of Indian cauliflower lines showed mitotype variations even within the ogura based cytoplasm. Variable nucleo-cytoplasmic interactions resulted into diverse type of floral malformationsin addition to pollen sterility even within the group of ogura based CMS lines. The finding provide important reference ameliorate understanding of mechanism of cytonuclear interactions in floral organ development in Brassicas. The study will help the breeders in selecting CMS lines without any floral abnormalities in B. oleracea.