This research was conducted to study effects of G × E interaction on 38 selected genotypes of cotton with two commercial cultivars Golestan and Sepid (control) in a randomized complete block design with three replications at three locations in Golestan Province in 2014-15. The measured characteristics were included: plant height, sympodial length, sympodial number, boll number, boll weight, seed cotton yield and earliness. Analysis of variance showed that genotype effect is significant in 1 or 5% probability levels on measured traits except for boll number and earliness. A significant interaction effect between genotype × locations in yield showed different variation trends in various locations. So that genotype 29 had the best performance in Hashemabad station but genotypes 24 and 18 showed their best performances in Gonbad and Anbarolum station respectively. Stability parameters were calculated and genotype No. 8 was defined according to regression slope close to 1 as the most stable genotypes among. This genotype had a smaller share in genotype and environment interaction according to Rick ecovalans and Shukla stability variance parameters and 10 and 33 were the most unstable genotypes in terms of performance. GGE biplot method showed that the first two principal components regression model explained 74% of the observed changes. GGE biplot graph plotted by software reflected the superior genotypes TJ82, ER26, DB29, DB19, DB25 and ER36 respectively. Also Hashemabad has been identified as appropriate region for ER26 genotype and TJ82 was identified as the best and most stable genotype.

Combining ability and heterosis were determined in a population obtained from the full diallel crossing of four different cotton genotypes (G. hirsutum and G. barbadense) for agro morphological traits and yield. High variation was observed for characteristics among parents and the F1 combinations. So, selection could be done for improved yield, yield components and agro morphological traits. Barbadense 5539 and Termeze14 (G. barbadense) had positive GCA for height, bolls/plant and sympodia branch/plant, Inverse, Sahel and Sepid (G. hirsutum) had negative GCA for these characteristics. G. barbadense genotypes showed negative GCA for monopodia branch/plant, sympodia branch length and boll weight, Inverse, G. hirsutm genotypes was observed positive GCA for this traits. The GCA: SCA ratios for the studied traits were higher than one indicating the presence of additive genetic effects for most of the characteristics studied, except for sympodia branch length.

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Jafari et al.: Effect of pix (mepiquat chloride) on the salinity resistance of the new cultivars of cotton (Gossypium hirsutum L.