PATHAK, H. C.Patel, Jagadishbhai Bhikhabhai2018-06-062018-06-061995http://krishikosh.egranth.ac.in/handle/1/5810049311Six females consisting of two chewing tobacco varieties, A 145 and GT 6, each with three cytoplasmic sources, were crossed with 8 diverse pollinators in a line x tester mating design. The resulting 48 hybrids alongwith 14 parents were grown in a randomized block design with three replications, at B.T.R.S., Anand during 1994-95 and were evaluated for 14 characters. The objective of the study was to investigate the mean performance of parents and hybrids, magnitude of heterosis, components of genetic variances, general combining ability effects of the parents and specific combining ability effects of the hybrids over diverse cytoplasm. The analysis of variance revealed greatdeal of genetic variability for yield, its components and the quality traits. The analysis of variance also suggested that there was no difference between fertile and sterile hyhrids and hybrids from CMS (m) and CMS (u) sources for all the characters except days to flower, stem girth and nicotine content in the former, and for the plant height, days to maturity, nicotine and reducing sugar content in the latter. On the basis of mean performance, hybrids were significantly superior to parents for days to flower, plant height, leaf length, leaf breadth, days to maturity nicotine content and reducing sugar content. Among parents, males were significantly superior in cured leaf yield, plant height, leaf length, whereas females were significantly superior for days to flower and days to maturity. Estimates of heterosis were highly significant for cured leaf yield, majority of its components and quality traits. Two hybrids viz., CMS GT 6 (u) x 575-28-110 and GT 6 (t) X 362-32-30 gave significant heterosis, heterobeltiosis and standard heterosis for cured leaf yield, important yield components and quality traits. The analysis of variance for combining ability indicated the preponderance of additive gene action for all the characters except leaf thickness, reducing sugar and total nitrogen content, where non-additive gene action was predominant. GT 6 (t) and its CMS counterparts among females and culture 3-58-38, NPN 16 and GT 7 among males for cured leaf yield, important yield components and nicotine content; A 145 (t) and its CMS counterparts among females pm culture 256-26-39, culture 575-28-110 and culture 362-32-30 among males for quality traits; A 145 and its CMS counterparts for days to flower, days to maturity, thick leaf and thin stem showed superior mean performance and superior general combining ability. Among hybrids, only CMS GT 6 (u) x 575- 28-110 involving good x poor general combiners showed significant positive/desirable sea effect for cured leaf yield, many of its components and quality traits. In general, the hybrids involving, good x poor general combiners exhibited highly significant sea effect for different characters studied. The preponderance of additive gene action for yield and quality traits suggests the adoption of pedigree method of breeding for the isolation of superior stable genotypes. However, the presence of high degree of heterosis and sea effect for cured leaf yield and quality traits indicates the feasibility of utilizing hybrid vigour on commercial scale. Here, two hybrids viz., CMS GT 6 (u) x 575-28-110 and GT 6 (t) x 362-32-30 showing significant heterosis and significant/positive desirable sea effects for yield and quality traits hold promise. GT 6 females, culture 3-58-38, NPN 16 and GT 7 for yield and quality traits; A 145 females for earliness, dwarfness, thick leaf and thin stem; culture 161-67-36 for dwarfness and low nicotine content and culture 362-32-30 for high nicotine content showing superior combining ability effects, can be exploited as parents in future hybridization programme. The absence of depressing effect of CMS lines on yield, important yield components and quality traits suggests that CMS line can safely and profitably be used in heterosis breeding programme. Here, CMS (u) females, having, protruding stigma can advantageously be utilized.enPLANT BREEDING AND GENETICS, AGRICULTUREA STUDYThesis