الفهرس 
INTRODUCTIONOnly 14 pages are availabe for public view
 |  | from | 9 |  |  |
| | | from | 9 | | |
Abstract
Fifty cotton varieties and genotypes of (G. barbadense L.) were evaluated against damping-off disease under artificial inoculation conditions. Three varieties were the most susceptible ones namely, Giza 90, Giza 85 and Giza 92 and three genotypes were the most resistant namely, (Giza 83 x “Giza 75 x 5844”), (Giza 77 x Giza 70) and (Giza 89 x Pima S6) to damping-off disease.
The three susceptible varieties were used as female parents and the three resistant genotypes were used as male ones, then crossed in a line x tester pattern at Giza Agricultural Research Station in 2009/2010 season and were used to estimate heterosis, combining ability, type of gene action and heritability for yield component characters. The six parents and their 15 F1 hybrids were included in randomized complete block design with four replications , the plot contained three lines, each is 4 meters long and 70 cm apart, spaces between plants were 30 cm then thinned at the rate of 1 plant. All the normal culture practices were applied as recommended for ordinary cotton cultivation at Sakha Agricultural
Research Station in 2010/2011 season .The obtained results can be summarized as follows:
1. Mean squares due to all the 15 genotypes including parents and
F1’s were highly significant for all studied traits. Parents vs. crosses mean squares over all crosses were highly significant for lint percentage and seed index. All crosses were found to be highly significant for all studied yield and its components traits.
2. The mean performance of parents and their F1 hybrids gave a wide range of variation for all studied characters. Female parent, G92 gave the highest mean performance for all studied characters except for lint percentage. Male parent [G83x “G75x5844”] gave
the highest mean performance for boll weight, number of bolls/plant, seed cotton yield/plant, lint yield/plant and seed index.
3. According to parental combinations, mean performance for F1 hybrids varied for all studied characters. Cross [G92x (G83x “G75x5844”)] gave the highest mean performance for number of bolls/plant, seed cotton yield per plant, lint yield per plant and seed index. Meanwhile, [G85 x (G83x “G75x5844”)] gave the highest mean performance for boll weight, lint percentage and lint index.
4. Heterotic values over the mid-parental value varied between all crosses. They were highly significant for boll weight in crosses [G92x (G89x PimaS6)], [G90x (G89x PimaS6)] and [G85x (G83x “G75x5844”)]; for seed cotton yield per plant in crosses [G92 x (G83x“G75x5844”)], [G92x (G89xPima S6)] and [G90x (G89x Pima S6)]; for lint yield per plant in cross [G92x (G89xPima S6)];
for lint percentage in crosses [G90 x(G77xG70)] and [G85 x(G77xG70)]; for seed index in crosses [G92x (G83x “G75x
5844”)], [G92x (G77xG70)], [G92x (G89xPima S6)], [G90 x (G89xPima S6)] and [G85 x(G83x”G75x5844”)] and for lint
index in crosses [G90 x(G77xG70)] and [G85 x(G77xG70)].
5. Heterotic values over the better-parent were highly significant for only boll weight in the cross [G90x (G89 Pima S6)] and seed index in the cross [G92x (G89xPima S6)].
6. The estimates of variance due to SCA were positive and higher in magnitude than the variance of GCA for all studied traits.
Moreover, additive effects had a minor role in the inheritance of these traits.
7. Comparison of the GCA effects of individual parents cleared that the male parent, [G83x (G75x5844)] was the best combiner for all studied traits. On the other hand, comparing the specific combining ability showed that the cross [G85x (G83x ”G75x 5844”)] was the best combiner for most of the studied traits.
8. Dominance estimates were higher than the additive estimates for all studied traits.
9. Estimates of heritability in broad sense for yield and its components revealed high heritability values in the broad sense for all traits under investigation. Regarding the narrow sense heritability estimates, number of bolls per plant, seed cotton yield per plant and lint cotton yield per plant were high indicating that these traits could be improved through selection programs in the early segregated generations. While it was low for the rest of the studied traits (boll weight, lint percentage, seed index and lint index) meaning that selection should take place in the late segregated generations to improve such traits.
10. Results of SDS-PAGE analysis revealed a total number of 5 bands with molecular weights (MW) ranging from 12.45 to 96.36 KD for six parents and their F1’s (9 crosses). Four out of five detected protein bands were seen in all tested cotton genotypes.
Meanwhile, one protein band with molecular weight of 32.83 KD was absent in all female parents which were highly susceptible to damping-off disease and was present in all male parents which were highly resistant against damping-off disease. In addition, that protein band was present only in the crosses [G92 x (G83x “G75x5844”)], [G92x (G77xG70)] and [G92x (G89xPimaS6)].