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ThesisItem Restricted Combining ability and heterosis studies in a diallel cross of periwinkle (Catharanthus roseus L.)(Punjab Agricultural University, Ludhiana, 2022) Bolagam Ravikumar; Dhatt, K. K.The current investigation entitled "Combining ability and heterosis studies in a diallel cross of periwinkle (Catharanthus roseus L.)" was investigated at the Floriculture Research Farm of Punjab Agricultural University, Ludhiana during the years 2019 to 2022. Six inbred lines of periwinkle namely P1 (Vi-15-1), P2 (Vi-13-2), P3 (Vi-16), P4 (Vi-15-2), P5 (Vi-29) and P6 (Vi-14-3) were crossed in full-diallel fashion with an objective of identifying superior cross-combinations for high specific combining ability and qualitative traits and determine the inheritance of flower colour and size. The six inbred lines and their thirty cross combinations were evaluated for plant height, plant spread, number of primary branches per plant, leaf length, leaf breadth, internode length, corolla tube length, days to flowering, duration of flowering, number of flowers per plant, flower diameter, follicle length and number of seeds per follicle in Randomized Block Design and replicated thrice. Analysis of variance was highly significant for all the vegetative and flowering characters indicating presence of genetic variability in the genotypes. The analysis of variance for combining ability was highly significant for growth and flowering characters indicated presence of both additive and non-additive gene actions. The parents P5 (Vi-29) and P1 (Vi-15-1) were recorded preferable GCA effects for most of the traits. These were considered as good general combiners for crossing programmes. The cross combination of Vi-13-2 × Vi-29 had significant positive maximum SCA effects for plant height, plant spread and number of primary branches per plant. The follicle length and number of seeds per follicle were recorded highly significant positive SCA values in the combination of Vi-29 × Vi-14-3. The high significant positive reciprocal effects were recorded for plant height, leaf breadth, number of flowers per plant and number of seeds for follicle in the cross combination of Vi-14-3 × Vi-29. The plant spread, duration of flowering and corolla tube length were shown high significant positive reciprocal results in cross combination of Vi-14-3 × Vi-13-2. The highly significant positive heterobeltiosis was present in the progenies of Vi-29 × Vi-14-3, Vi-13-2 × Vi-29 and Vi-15-1 × Vi-14-3 for most of the studied traits. High to moderate values for phenotypic and genotypic coefficients of variation were shown for majority of the studied characters, recapitulate the presence of variability. The range of phenotypic and genotypic coefficient of variations among the parental lines was 5.35-34.41% and 3.96-34.02%, respectively. The PCV and GCV was 4.14-25.49% and 4.01-24.94% for the cross combinations, respectively. The heritability varied from 46.74-97.77% and 50.62-98.73% for the parental lines and cross combinations, respectively. It indicated that the traits were highly heritable to following generations. The average genetic advance as per cent mean was observed as 8.00-50.21% and 6.03-69.29% among the inbred lines and cross combinations, respectively. The flower colour and size were segregated with 3:1 (monohybrid), 9:3:4 (supplementary gene action), 9:6:1 (polymeric gene action) and 9:3:3:1 (typical dihybrid) in F2 generation of fifteen selected crosses from diallel crosses.
