Studies on heterosis and molecular diversity in forage sorghum [Sorghum bicolor (L.) Moench] hybrids

Pankaj Kumar

Studies on heterosis and molecular diversity in forage sorghum [Sorghum bicolor (L.) Moench] hybrids

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Date

2015-07

Authors

Pankaj Kumar

Publisher

G.B. Pant University of Agriculture and Technology, Pantnagar-263145 (Uttarakhand)

Abstract

The present investigation was carried out during Kharif seasons of year 2012-13 and 2013-14 at the Instructional Dairy Farm of G.B. Pant University of Agriculture and Technology, Pantnagar. The experimental material was developed by mating five pollinator parents of forage sorghum with ten cytoplasmic male sterile lines (CMS) in line x tester mating design. The field experiment with 68 treatments including 50 F1s, ten CMS lines, five pollinators and three standard checks was planted in randomized block design with three replications during both 2012-13 and 2013-14 kharif seasons. The observations were recorded during both the years, as per appropriate procedure, on shoot fly infestation, protein per cent, HCN content, foliar disease index per cent, regenerability score, plant height, number of leaves per plant, leaf length, leaf width, leaf area, stem diameter, total soluble solids, number of tillers per plant, IVDMD per cent, leaf:stem ratio, green fodder yield and dry fodder yield. Besides field experiment, sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE) to detect protein profile variation and microsatellite (SSR) marker analysis for molecular characterization, of twenty five parental (A, B and R lines) genotypes were also done. The analysis of variance revealed highly significant genotypic differences for all the characters studied which clearly indicated presence of sufficient variability for each trait in the experimental material. Significance of line vs. tester mean square revealed that testers were highly divergent from lines. Significance of parent vs. crosses and line x tester interaction mean squares for most of the characters including yield, suggested existence of considerable amount of average heterosis and predicted significance sca values among the crosses. Sufficient inherent genetic variability for two major foliar diseases viz. zonate leaf spot and anthracnose was observed in the experimental material. The parental genotypes SP 55609 A, ICSA 293 and PC 5 for zonate leaf spot and 11 A2, SP 55609 A, ICSA 702 and HC 260 showed low disease index per cent for anthracnose. Variable magnitude of three types of heterosis (heterobeltiosis, mid-parent heterosis and standard heterosis) exhibited for various characters by different cross combinations indicated sufficient divergence in parental material for these traits. Three crosses viz. 32 A2 x PC 6, ICSA 469 x PC 6 and MR 750 A2 x PC 8 showed significant and positive estimates of all three types of heterosis during both 2012-13 and 2013-14 as well as pooled over years, for green fodder yield. Whereas, three crosses viz. 32 A2 x PC 6, ICSA 293 x HC 260 and MR 750 A2 x HC 260 showed significant and positive estimates of three types of heterosis for dry fodder yield. Significant gca and sca values were observed for most of the characters. The variance ratio (σ2 gca / σ2 sca) of less than unity revealed preponderance of non-additive gene action for most of the traits, except plant height, total soluble solids per cent and green fodder yield. Near unity variance ratio for yield indicate importance of both additive and non-additive gene actions for inheritance of forage yield, thereby suggesting for scope of selection as well hybrid breeding for improvement of yield and its component in forage sorghum. The male sterile lines, 32 A2 and MR 750 A2 had significant gca effects with substantially good per se performance for fodder yield (green fodder yield and dry fodder yield), its components traits, forage nutritional quality and resistance to shoot fly infestation. Therefore, these lines may contribute to increase in yield besides improvement in nutritional quality and resistance of the crosses, if used as parents. Amongst testers PC 6 was one of the best combiner with significant high positive gca effects for green and dry fodder yield coupled with high mean performance. Based on significance of sca effects, higher per se performance and heterotic response for green and dry fodder yield, the best crosses identified were 32 A2 x PC 6 and ICSA 293 x HC 260. SDS-PAGE analysis of seed protein manifested that the 25 sorghum genotypes (10 male sterile, 10 maintainer and 5 restorer) differed from each other with respect to total number of protein bands, their thickness and intensity. Most of the CMS lines and restorer lines showed differentiation in protein profiles. CMS lines and the corresponding maintainer lines in general showed similarity in banding pattern however, some of the male sterile and maintainer lines viz. ICSA 469, ICSB 469, ICSA 702, ICSB 702, ICSA 276, ICSB 276, ICSA 264 and ICSB 264 showed variation in respect of number and intensity of protein bands. This variation may be due to difference in molecular weight of proteins, their polypeptide bands composition and disturbed protein metabolism. Diversity analyses of twenty five parental genotypes performed through twenty five SSR molecular markers analysis revealed that the genotypes could be grouped prepared into two major and several different minor clusters. The genotypes HC 260 and CSV 15 were found most diverse with 53.00 similarity coefficient. While the genotypes 2219 A and 2219 B, 11 A2 and 11 B2, ICSB 264 and ICSB 293 and MR 750 A2 and MR 750 B2 least similarity coefficient of (100.00). Twenty two primers were able to detect high level of polymorphism among the parental genotypes.