Genetic studies of earliness, yield and fiber length upland cotton ( gossypium hirsutum L.)
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The Inheritance of yield, fibre length and airlines in Upland cotton (Gossypium hirsutum L.) w s studied using Pi. P2r F1' F2, B1' 82 populations in five Inter varietal crosses. The commercial variety., UKAS9/240. (Pi) was a common parent In 11 the five crosses involving th early maturing varieties. i.e., PRS 74, SR 1054-2, K 3400-7, K 4371. K 4614. The six population were grown In randomised blocks experiment with four replications t the Cotton Research Station, Kibos. The six characters studied were seed cotton yield, lint yield, lint percentage, lint index, fibre length and days to first poll opening_ For these characters, the means,variances and standard errors were calculated, and the estimates of these parameters were in turn used in subsequent genetic analyses. Scaling test was used to determine the presence of additive, dominance and epistatic gene effects. The gene effects were then estimated by Gamble·s (1962) six parameter model. using gen ration means. The six parameters represented the mean effects (!9.), additive (~) and dominance (~) gene effects, and the three types of dlgenic epistatic effects, (a ), (-ad) nd (-dd). Heritability in narrow sense w estim ted using additive and phenotypic variances. The magnitude s nd significance of the gen effects were examined and compared in order to estimate their relative import nee in the inheritance of the characters. Significance of the gene effects was tested by test. The means were used In estimating het roses and inbreeding depression, nd potence ratio. Correlations and regressions ( 11 ) among th.:lvarious characters were calculated from the observations on single plants of F2 populations. 1~e results indicated that additive gene effects were present in all the characters studied, and their contribution to genetic variance was :important. Dominance gene effects were also important in seed cotton yield, lint p~rcentage, fibre length and days to first boll opening, but were unimportant in lint index where additive gene effects were predominant. Both additive x additive epistasis and dominance x dominance epistasis appeared to be less important than additive x dominance epistasis, which made more contribution to the inheritance of seed cotton yield, lint yield, lint percentage- Dominance x dominance gene effects were more important for fibre length and earlinesso Heterosis for Beed cotton yield and lint yield over mid-parent was not importanto Heterosis over better parent was negative in all characters, therefore, unimportant. Inbreeding depression occured in all characters and in all crosses. The highest positive correlation coefficients were recorded between seed cotton yield and lint yield (0.987·· to 0.996··)0 Days to first boll opening did not show significant correlation with other characters in most crosses, and the correlation coefficients were often negative. All the yield components and fibre length showed significant positive correlation with each othero High correlation coefficients also occurred between lint percentage and lint index (0.230·· to 0.687··)0 Correlation coefficients between othQr characters varied and were generally lower than ( 111) rho se between he yield components Seed cotton y eld howed high coefficients of determination for lint yield, while lint index showed fairly hi9h coefficient ts f determination for lint percent ge. Hybridi atlon and selection 1n the present cross would be useful in d velo i;:'1v9 rleties with improved characters su h s earliness, hi9h yield of seed cotton and long fibr. ecurrent selection and mass selection wo 1 be effective in Improving cotton populations. It appeared t~at lint percentage and lint index could be more easily improved by selectin9 transgressive segregates in the F2 populations then seed cotton yield could be.