الفهرس 
Material and methodsOnly 14 pages are availabe for public view
 |  | from | 119 |  |  |
| | | from | 119 | | |
Abstract
SUMMARY AND CONCLUSION
The stated objectives of this study was to evaluate stability of gca and
sea under three different environments for several agronomic and fiber
properties for six cotton varieties.
A half-diallel genetic design of six parents, their 15 F1 hybrids and 15
F2 populations were used. Parents are the commercial varieties of Giza 77
(PI), Giza 81 (P4) and Dendera (P6), and the other, are the three promising
varieties; Giza 84 (P2), Giza 85 (P3) and Giza 83 x (Giza 72 x Delcero)
(Pe). Chosen parents, represent the range of variability existing in
Egyptian cottons for most studied traits. Crossing parental materials inters
by the diallel system was initiated at EI-Giza Agricultural Research
center, to generate Fl’ S and their corresponding F2’ S in 1992 and 1993
seasons. In 1994, the six varieties and their derived crosses were grown in
the three different locations of Sacolta (Sohag governorate), Kenayate
(Sharkiea governorate) and Sakha (kafr El-Shiekh governorate). The
experimental layout was a randomized complete blocks design with three
replications. Characters evaluated for gca and sea were :-
1- Seed cotton yield / plant. (g)
2- Lint yield / plant (g)
3- Number of bolls / plant.
4- Boll weight. (g)
5- Lint percentage. 0/0
6- Seed index (g)
7- Lint index (g)
8- Fiber fmeness in micronaire reading.
9- Fiber strength in Pressely index.
10- Fiber length ”2.5 % span length”. (mm)
11- Mean length ”50 % span length” (mm)
12- Uniformity ratio.
Data obtained was statistically analyzed on plot mean basis. The
ordinary analysis of variance was firstly performed on leachexperiment.
Combined analyses were carried out afterwards. Separate and combined
by locations genetic analyses to obtain gca and sea were conducted by
using (Griffing 1956, Singh 1973 a and b) in diallel cross analyses
designated as model I method II. Mid- and better-parent heterosis were
computed. Also, values of inbreeding depression and phenotypic
correlation were given.
Combined three locations analysis of parents, their FI’ S and F2’ s
revealed highly significant differences among genotypes for all traits
except for uniformity ratio.
Seed cotton yield / plant, lint yield / plant, number of bolls / plant and
boll weight are the most affected characters by the genotype x location
interaction than the other characters.
Parent showed substantial differential response to the environmental
changes for seed cotton yield / plant, number of bolls / plant, lint
percentage and Pressley index.
F1’ s and F2’ S combinations showed substantial differential response for
seed cotton yield, lint yield, number of bolls / plant, boll weight and lint
index.
The level of heterosis was quite different from location to location. The
most drastic differences were those pertaining to seed cotton yield / plant,
lint yield / plant, number of bolls / plant and lint percentage.
Estimates of mid-parent heterosis over locations were observed for
seed cotton yield / plant, lint yield / plant, number of bolls / plant, boll
weight, lint percentage, lint index and 2.5 % span length. However, highly
significant estimates of better-parent heterosis over locations were evident
for seed cotton yield / plant (18.0 0/0), lint yield / plant (17.8 0/0) and
number of bolls / plant (13.0 0/0).
A considerable number of hybrids manifested significant positive
heterosis for seed cotton yield, lint yield, number of bolls / plant, boll
weight and 2.5 % span length. Hybrids showing heterosis for the other
traits were less frequent.
Mean inbreeding depression effects was small and insignificant for all
traits. Also, mean F2 deviations was small and non-significant for all
characters which suggested that epistatic effects were not operative.
Highly significant estimates of gca mean squares were calculated for
all traits. Sea mean squares were detected only, for agronomic characters.
Significant differences in gca and sea effects between locations for
most traits suggested that a range of environments (multi-location
experiments) is needed to better evaluate hybrid combinations.
Gca / Sea ratio of variance components indicated that additive genetic
variance was less in importance for seed cotton yield / plant, lint yield /
plant, number of bolls / plant, weight per boll and seed index and of
greater importance for lint percentage, lint index and fiber properties.
Nevertheless, non-additive vanance was more important for yield and
most of the associated characters.
The size of gca effects corresponded closely with the rank of parental
means for all traits except boll weight (P4) is the best combiner for seed
cotton yield, lint yield, number of bolls / plant, lint percentage and lint
index. (P5) is good to improve number of bolls per plant and lint
percentage. (Pi) had high estimates of gca effects for Pressley index,
2.5 % and 50 % span length, while (P2) is valuable parent for micronaire
reading (fmer).
Moderate levels of heterosis and sea effects were observed in certain
crosses, for high cotton yield (P4 x P5) and (P3 x P6) had the best sca
effects and highly significant positive heterosis for seed cotton yield /
plant, lint yield / plant and number of bolls / plant. (P3 x P5) gave highly
significant and positive sea effects as well as heterosis for number of bolls
/ plant. (P, x P2) could be used in breeding programs to improve fiber
length characters.