الفهرس 
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Abstract
The present study was done in the Agronomy Department, Faculty of Agriculture, Mansoura University .The investigation was carried out at Sakha Agriculture Research Station, ARC Egypt, during 2014 and 2015growing seasons.Line x tester (TOP crosses) analysis: This design divided the variation of single crosses, into three portions, viz., 1) variation among testers (parents), 2) variation among lines (parents) and 3) variation due to line by tester interactions. Using a broad based genotype tester, the general combining ability of lines is tested in the top cross method. The analysis of variance indicated that the mean squares of genotypes for all studied characters were significant expect for electrolyte leakage and seed imbibing %, indicating the present of considerable amount of genetic variability among genotypes, parents and hybrids. The variations due to parent’s hybrids were also significant for most characters however. The variation due to parents vs. hybrids was also significant for most characters under investigation indicating the heterotic response for these characters.The data revealed that the ten parents were significantly deferent in earliness characters. The Russian genotype karshenky2 surpassed all cotton parents for earliness characters showed decrease in days to first flower and first fruiting branches with increase in earliness index followed by the promising cross Giza 89 X Pima S6.The upper Egypt parent ,Dandra, showed somewhat earliness characters. On the other side the Commercial variety Giza86 showed the reverse trend since recorded increased in days to first flower with high first fruiting node as well as decrease in earliness index followed by Giza45 and Giza 68 genotypes.The estimates of heterobeltiosis were ranged from -3.59 % to -19.34 % for days to first flower, most cross combinations showed significant negative heterosis ( desirable ) over better parent for days to first flower . Out of 21 F1 cross combination five hybrids were found significant negative heterosis (desirable) over better parent for first fruiting node and three cross combinations only recorded significant positive ( desirable values ) heterosis over better parent for earliness index . The cross combination Kar2 x Giza67 recorded the best values for all earliness traits followed by Kar2 x G.86.The data revealed that among the three male (testers) parents Karshenky2 was the best combine for earliness index and seed volume. However, it was the poorest male for boll weight, seed cotton and lint yield / plant. However, among the female parents (lines) Giza 67 was the best general combines for earliness index. Dandra and Giza 92 were good general combines for boll weight. The genotypic correlation were higher than phenotypic correlations for most case, indicating that genetic effects were greater than the environmental effects in the expression of these characters. This due to a result of modifying effects of the association of genetic characters.Development of high yielding varieties with acceptable fiber quality properties is one of the important objectives in cotton breeding programs.Cotton is one of the few crops which are accessible to the development of genotypes as varieties and at the same time amenable for commercial exploitation of heterosis.