الفهرس 
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Abstract
Cotton is the cheif fiber crop throughout the worlds In Egypt, it occupies about one fourth of the total cultivated area. Inprovement of yield in cotton through conventional br&eding methods as well as application of the optimum agronomic practices has reached a level at which phenomena]. increase seems to be rather diffecult. This warrants to think of some new breeding approach which might increase the yield considerably. The discovery of an effective biological system in cotton involving sytopla— smic male sterility and pollen fertility restoration open a new approach to further improvement of cotton. It provides the possibility of commercial utilization 0± F1 hybrids to achieve new levels of productivity. Combining ability is often desirable to select the lineth as parents of crosses, in addition to selections for other characters that are desired to produce successful cotton hybrids.
It is worth to note that the problem is large, but it is suffcjent to say that production of hybrid cotton has not yet reached the farmar’s fields There are a great difflculties before reaching this point.
Altiough a number of experiments has been conducted to meaau. hybrid vigor in cotton, the use of small population’s and space planting has generally limited
applieabilit-1r of the results to commercial practice.
In the present investigation a diallel cross of give local and introduced cotton varieties belonged to Ge barbadense and G, hirsutuni was undertaken including tIie reciprocal to study;
1. The manifistation of hybrid vigor;
2; Combining ability;
3 Gene effects of 16 agronomic traits under two population densities.