S.S. Dey

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

Summary 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 _- 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_ MS medium supplemented with 1.0 mg l-1 indole-3-butyric acid. In vitro-raised plants were hardened and used successfully for F1 hybrid development.When the F1 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 F1 hybrids developed through in vitro-maintained CMS lines. In F1 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 F1 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.

Molecular breeding for resistance to black rot [Xanthomonas campestris pv. campestris (Pammel) Dowson] in Brassicas: recent advances

The Brassicas are affected by several diseases, of which black rot, Xanthomonas campestris pv. campestris (Pam.) Dowson (Xcc), is one of the most widespread and devastating worldwide. The black rot bacteria causes systemic infection in the susceptible plants and penetrate the plants through the hydathodes or wounds. Typical disease symptoms are ‘V’ shaped necrotic lesions appearing from the leaf margins with blackened veins. Periodic outbreaks of the black rot pathogen have occurred worldwide, especially in the continental regions, where high temperatures and humidity favor the incidence of disease occurrence causing huge yield loss. The challenge to control the losses in vegetable brassicas production is made more difficult by the adverse climatic changes and evolution of new pathogenic races. The development of black rot resistant hybrids/varieties is the most reliable long term practical solution for effective disease control. Identification of new resistant genetic resources, tightly linked markers with resistance loci and QTL mapping would facilitate the breeding programme for black rot resistance. Information regarding genetics of resistance and mapping of resistance genes/QTLs will accelerate the marker assisted resistance breeding in brassica crops against Xcc. In future we need to identify the race specific candidate genes for and their validation through transgenics and gene expression. Moreover, it is imperative to identify functional markers for resistance genes through identification of R gene families and their relationship with resistance expression. This comprehensive review will help the researchers working in this area to understand the dynamics of black resistance breeding and to formulate future breeding strategies.

Genetic analysis of important antioxidant compounds in cabbage (Brassiaca oleracea var. capitata L.)

ABSTRACT The paucity of research on development of antioxidant-rich hybrids in cabbage by utilizing combining ability estimates, gene action, and heterosis motivated us to undertake this study. We made 60 crosses between 5 cytoplasmic male-sterile lines and 12 male-fertile testers during the summer of 2015, as per the line × tester design. The seedlings of all the parents and 60 F1 crosses, along with three checks, were transplanted during the Rabi (winter) season of 2015–2016 and evaluated using a randomized complete-block design. Combining ability, gene action, and heterosis were determined for different antioxidant compounds. Experimental results revealed that the range of cupric ion reducing antioxidant capacity (CUPRAC) [parents = 1.26–7.33 and hybrids = 0.04–6.54 μmol trolox/g], ferric reducing ability of plasma (FRAP) [parents = 1.65–4.76 and hybrids = 0.16–4.67 μmol trolox/g], β-carotene (parents = 0.44–2.29 and hybrids = 0.04–1.89 μg/100 g), and chlorophyll-a (parents = 0.71–4.08 and hybrids = 0.19–3.08 mg/g f.w.) for hybrids was lower than that of the parents because of outbreeding depression. The parental lines 6A, 208A, 83-5-8, and Sel-5-83-6 were found to be good general combiners for most of the antioxidant compounds studied. Based on the mean performance, specific combining ability effects and heterosis, five hybrid combinations viz., 9A × KIRC-8 for CUPRAC and FRAP; 208A × C-122 for ascorbic acid; 6A × Chhaki-2 for total carotenoids and β-carotene; 831A × Chhaki-2 for chlorophyll-a; and 6A × 83-5-8 for chlorophyll-b and total chlorophyll content, were most promising. The ratio of general combining ability (GCA) and specific combining ability (SCA) variances, i.e., [2 σ2g/(2σ2g + σ2s)], which reflects the relative importance of GCA versus SCA, was less than unity for different antioxidant compounds, which implied that for these traits, nonadditive gene effects were more important than additive effects. The numerical values of range for contribution of lines × testers interaction for different traits (41.47–70.18%) were found to be higher than the individual contribution of lines (11.24–47.22%) and testers (8.31–21.76%). Hence, heterosis could be exploited for developing antioxidant-rich hybrid cabbage.

Genetic divergence and interaction among CUPRAC, FRAP and total phenolics content in cauliflower (Brassica oleracea var. botrytis L.)

Antioxidant capacity and total phenolics content were estimated in 46 cauliflower lines to determine genetic variability, heritability and correlation among them with the objective to formulate breeding strategies for development cultivars with higher antioxidant capacity. The genotypes comprised of six CMS lines, few advance breeding lines and other core collection of our institute. Significant variability was recorded for CUPRAC, FRAP and total phenolics content indicating the scope for improvement in these traits based on various breeding strategies. Phenotypic co-efficient of variation (PCV) was higher (43.01, 73.07 and 64.28) than genotypic co-efficient of variation (GCV) (41.34, 71.83 and 63.88) in all cases indicating the role of environment in expression of these traits. However improvement for these traits is possible through selection and heterosis breeding as broad sense heritability (92.44% to 98.75%) and genetic advance as percentage of mean (82.46% to 130.87%) was high for all the traits. Correlation coefficient analysis revealed that CUPRAC, FRAP and total phenolics had significant positive correlation among each other. However, none of them had any significant correlation with marketable yield. Fourty six genotypes were classified into 6 groups based on non-hierarchical cluster analysis and phenotypic divergence. This study will pave the way for breeding of cauliflower cultivars and hybrids with higher antioxidant capacity and phenolics content.

‘Ogura’-based ‘CMS’ lines with different nuclear backgrounds of cabbage revealed substantial diversity at morphological and molecular levels

A comprehensive study on characterization and genetic diversity analysis was carried out in 16 ‘Ogura’-based ‘CMS’ lines of cabbage using 14 agro-morphological traits and 29 SSR markers. Agro-morphological characterization depicted considerable variations for different horticultural traits studied. The genotype, ZHA-2, performed better for most of the economically important quantitative traits. Further, gross head weight (0.76), head length (0.60) and head width (0.83) revealed significant positive correlation with net head weight. Dendrogram based on 10 quantitative traits exhibited considerable diversity among different CMS lines and principle component analysis (PCA) indicated that net and gross head weight, and head length and width are the main components of divergence between 16 CMS lines of cabbage. In molecular study, a total of 58 alleles were amplified by 29 SSR primers, averaging to 2.0 alleles in each locus. High mean values of Shannon’s Information index (0.62), expected (0.45) and observed (0.32) heterozygosity and polymorphic information content (0.35) depicted substantial polymorphism. Dendrogram based on Jaccard’s similarity coefficient constructed two major groups and eight sub-groups, which revealed substantial diversity among different CMS lines. In overall, based on agro-morphological and molecular studies genotype RRMA, ZHA-2 and RCA were found most divergent. Hence, they have immense potential in future breeding programs for the high-yielding hybrid development in cabbage.

Genetic divergence studies in tulip (Tulipa gesneriana L.)

Twenty one tulip genotypes were assessed for their genetic divergence based on 16 agro-morphologicaltraits following Mahalanobis D2-statistic. On the basis of D2 values, the 21 genotypes were grouped in tofive clusters, of which cluster II accommodated 6 genotypes, while cluster IV had single genotype. The highmagnitude of D2 cluster means indicated that there is a considerable diversity in the population studied. The D2 and inter-cluster coverage divergence were utilized for the choice of parents to decide the cross combination toproduce heterotic effect. The highest inter cluster D2 value was recorded between clusters III and V (11005.75)indicating that crosses may be attempted between the genotypes of cluster III (Character, Christian Dream, Hamilton and Horizon) and cluster V (Apeldoorn, Blushing Apeldoorn, Golden Apeldoorn, Strong Gold, TulipHb) to obtain new desirable recombinants in tulip. The study of cluster mean value of 5 clusters indicated highrange of variation for days to sprout, days to flower, wrapper leaf area, percent sprouting & flowering, plantheight and scape length among the different clusters. The cluster V includes genotypes with earliness andexhibited longest duration of flowering, highest wrapper leaf area and bulb weight. Genotypes of this clusteralso possessed desirable floral traits (scape length, floral size and scape thickness) and bulb traits (numberof bulbs per plant and bulb weight). Hence, genotypes from this cluster could serve as valuable parents todevelop superior cultivars. Out of 16 principal components first six accounted 91.88% of total variability. Thefirst principal component accounted for 57.25% of variability, while, the second and third accounted for 12.37and 7.54% of total variability, respectively. Hierarchical cluster analysis (HCA) was performed for getting moreclear idea among the genotypes. Based on HCA one dendrogram was constructed with two major clusters. These clusters could be divided into 8 minor sub-clusters.