ABSTRACT
This study was carried out during three successive seasons, 2000, 2001 and 2002 at the Experimental Farm of Faculty of Agriculture in Sohag, South Valley University. The main objective of this study was to estimate heterosis, inbreeding depression, potence ratio, type of gene action, genetic advance under selection and heritability in broad and narrow senses for yield and some yield components in two intra-specific cotton crosses between three varieties belong is to (G. barbadense). Cross 1 was (Giza 80 x Giza 89) and Cross 2 was (Giza 83 x Giza 80). The six populations, Pi, P2, Fi, F2, Bci and Bc2 were grown in 2002 season. Data were recorded on seed cotton yield/plant, lint yield/plant, no. of bolls/plant, boll weight, lint percentage, seed index and lint index. The results indicated highly significant and negative heterosis relative to mid and better parents for boll weight, seed index and lint index in the second cross, and positive and highly significant heterosis over mid-parents for the same traits in cross 1. Highly significant negative heterosis relative to better parent for boll weight and lint index, but was highly significant positive for seed index in cross 1. Significant inbreeding depression was found for lint index in both crosses and seed index in cross 1 and significant inbreeding gain for no. of bolls/plant in cross 1 and boll weight and seed index in cross 2. Overdominance was found for seed cotton yield/plant in both crosses, seed index in cross 1, and no. of bolls/plant and boll weight in cross 2. While, partial dominance was obtained for the remaining characters. The role of non allelic interaction was recorded in governing most studied characters in the two crosses. The additive gene effects were significant and positive or negative for all studied characters except for seed cotton yield/plant in both crosses, lint mid/plant and no. of bolls/plant in cross 2 and seed index in cross 1. The dominance gene effects were important in the inheritance boll weight and seed index in both crosses, and were relatively high in magnitude compared with the additive effects in all characters. The additive x additive interaction effects were significantly negative for boll weight, seed cotton yield/plant and seed index in cross 1. Most of studied characters were significantly affected by one or two types of epistatic effects (j and 1), in both crosses except seed cotton yield/plant and lint yield/plant in both crosses, and no. of bolls/plant in cross 1. The estimates of heritability in broad sense were larger than their corresponding in narrow sense for all traits in both crosses. Maximum predicted genetic advance as percent of F2 mean (Ag%) were achieved for no. of bolls/plant in both crosses and seed cotton yield/plant and lint yield/plant in cross 2.