الفهرس 
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Abstract
Cotton is the most important crop in Egypt. The aim of this investigation was to determine the extent of heterosis and combining ability estimates for some economic and fiber properties in Egyptian, American-Egyptian and Russian cottons. Ten parental cultivars andlor lines namely Giza 45, Giza 76, Giza 80, Giza 83, Giza 85, Giza 86, Giza 87, Giza 89, Pirna S6 and Karshensly2. All these Genetic materials belong to Gossypiunz barbadense L., representing wide range of variability in most of the studied traits were utilized. Crossing Among
the parental materials by line x tester system using the varieties, Giza 83, Giza 86, Giza 89 and Karsliensky.2 as testers and the other parental cultivars as lines was initiated in 1997 growing season. In 1998 season, two planting dates were carried out at Salcha Agricultural Experiment Station. The first was 17 April and the other was 17 May. Each planting date was designed in a randomized complete block wit11 four replications to evaluate the ten parental lines and their 24 FI hybrids. Data were recorded on ten guarded plants randomly sampled from each plot. The data obtained for each trait were statistically analyzed on individual plant mean basis. A line x tester analysis of variance firstly performed for each planting date, and then after combined data was carried out. Heterosis was completed, mean squares and as the percentage deviation of F1 mean performance from its mid-parents and better-parent average values for individual crosses. General and specific combining ability estimates were according to employing Kempthrone 1957 matting system. The studied characters were : a) growth habits and earliness measurements. days to first tnre leaf, days to appearance of first square, number of hiting node, days to first flower, square growth period, dates to first opening bolls, boll Summary growth period, number of vegetative branches per plants, number of fruiting branches per plant, plant height and earhness index, b) yield and yield component traits : seed cotton yield per plant, lint yield per plant, lint percentage boll weight, number of bolls per plant seed index and lint index; C) fiber properties traits: span length 2.5%, span length 50%, fiber strength and fiber fineness (Micronaire value) The obtained results can be sutnmarized.