25 Pakistan J. Agric. Res. Vol 23 No. 1-2, 2010. HERITABILITY AND SELECTION RESPONSE IN SEGREGATING GENERATIONS OF UPLAND COTTON Z. A. Soomro, M.B. Kumbhar, A.S. Larik*, M. Imran** and S.A. Brohi*** ABSTRACT: Heritability (b.s), genetic advance, phenotypic and genotypic vari- ance for different quantitative traits is important in determining the effective- ness of selection. In this study the potential effectiveness of selection in parents and their F 2 and F 3 progenies of Gossypium hirsutum for plant height, sympodia/ plant, bolls/plant, boll weight, seed index and seed cotton yield/plant was deter- mined. It was found that all the populations alongwith parents differed signifi- cantly (P < 0.01) and exhibited genetic variability among the genotypes for all the traits except sympodia/plant. Genetic parameters computed through variance com- ponents method show that all the traits were highly heritable in F 2 and F 3 genera- tions except sympodia/plant, indicating quantitative pattern of inheritance, of- fering better chances of selection for these traits in F 2 and F 3 generations. The traits namely plant height, bolls/plant and seed cotton yield/plant displayed high heritability (72.97 - 75.55%) with remarkable genetic advance (112.46 - 357.01%) indicating that these traits were predominantly governed by additive gene effects and direct selection may be effective. Boll weight and seed index exhibited low genetic advances irrespective to their high heritability estimates, probably due to non-additive gene effects, developing transgressive segregants through hybrid- ization is suggested. However, hybridization system, which exploits both fixable and non-fixable components, simultaneously, could be useful in the genetic im- provement of yield and yield components in upland cotton. Key Words: G. hirsutum; Heritability; Genetic Advance; Segregating Generation; Pakistan. INTRODUCTION Success in crop improvement programme depends on the amount of ge- netic variability and its utilization. In popu- lation improvement it is important to de- termine the extent of genetic variation for traits to be improved. The genetic informa- tion on broad sense (b. s.) heritability and genetic advance are very important to pre- dict the behavior of the parents to be uti- lized in breeding programme for selecting high yielding cultivars. High genetic ad- vance coupled with high heritability esti- mates offers a most effective response to selection (Larik et al. 1997). Khan et al. (2002) and Soomro et al. (2005) observed additive type of gene action for seed cotton yield and some yield components of Gossypium hirsutum due to high heritabil- ity and selection response. Considering the importance of this type of research, it was contemplated to ascertain heritability and genetic gain in upland cotton genotypes. The information so obtained shall be use- ful in formulating a sound future breeding programme in this crop for tangible ad- vancement. MATERIALS AND METHODS Five cotton (Gossypium hirsutum L.) cultivars namely TH-3/83, NIAB-78, CIM- 109, Mc-Nair-3150 and Reshmi were crosses in all possible combinations. The five parental cultivars and their 20 F 2 ’s and 20 F 3 ’s were grown in a RCB design with four replications at Sindh Agriculture Uni- versity, Tandojam, Pakistan in 2005-06. Seeds were dibbled in rows 75 cm apart @ of 3.5 kg ha -1 . Before first irrigation seed- lings were thinned to maintain plant to *Department of Plant Breeding and Genetics, Sindh Agriculture University Tandojam, Pakistan. **Fodder Programme, National Agricultural Research Centre, Islamabad, Pakistan. ***Department of Agronomy, Sindh Agriculture University, Tandojam, Pakistan.