In vitro maintenance of CMS lines of Indian cauliflower: an alternative for conventional CMS-based hybrid seed production

摘要

Three Ogura cytoplasmic male-sterile (CMS lines) of Indian cauliflower (Brassica oleracea var. botrytis L.; Ogu1A, Ogu2A and Ogu3A) were compared for their in vitro regeneration ability using two types of explant, hypocotyls and curds (i.e., pre-floral fleshy apical meristems). The highest rate of in vitro establishment and the highest multiplication index were recorded in Ogu3A. Ogu2A showed poor in vitro establishment. The choice of explant had a significant impact on the morphogenetic potential of all three lines. Among the two types of explant, curds proved to be more efficient for the initial establishment of cultures. The highest rate of in vitro establishment and multiplication index were recorded for Ogu3A on Murashige and Skoog (MS) medium supplemented with 2.5 mg l(-1) kinetin, 0.2 mg l(-1) alpha-naphthaleneacetic acid and 0.2 mg l(-1) gibberellic acid. The three CMS lines also showed significant variations in the numbers of roots induced per shoot. The maximum number of primary roots per shoot was recorded in Ogu3A on 0.5 x MS medium supplemented with 1.0 mg l(-1) indole-3-butyric acid. In vitro-raised plants were hardened and used successfully for F-1 hybrid development. When the F-1 hybrids developed using in vitro-maintained or conventionally maintained CMS lines were compared, it was observed that variations in plant height, days to 50% curd maturity (DCM), and net curd fresh weight (FW) were lower in those F-1 hybrids developed through in vitro-maintained CMS lines. In F-1 hybrids developed from in vitro-raised CMS lines, the range of standard deviation (SD) values as percentages of the mean value for DCM and net curd FW were 2.5 - 3.7% and 6.6 - 10.7%, respectively. In contrast, the corresponding SD values ranged from 5.8 - 7.9% and from 13.6 - 19.9% for F-1 hybrids developed from conventionally maintained CMS lines. This in vitro protocol, using curd explants, will be useful for the rapid multiplication of breeding lines of cauliflower without inbreeding depression, and for high-quality hybrid seed production.