الفهرس 
Material and methodsOnly 14 pages are availabe for public view
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Abstract
SUMMARY
This study investigated the extent of heterosis, combining ability
and their interactions with three nitrogen levels ( as three different
environmental conditions) and genetic components in sunflower
(Helianthus annuus, L.) for flowering date, plant height, number of
leaves/ plant, head diameter, 100- seed size, number of seeds/ head,
1000- seed weight, husk percentage, seed yield per plant and oil
percentage. Path coefficient analysis for seed yield, were also calculated.
The seven inbred lines in this study were derived from Giza- 1 (PI),
Introduced 30 (P2), Peredovic (P3), Raistra 70 (P4), CR2 (P5), nno (P6)
and CHO (P7) after ten selfed generations. These parents were chosen to
represent a wide range of variability in most of the studied traits (oil
percentage, yield and certain other agronomic characters). In 1993
season, these inbred lines were sown and crossed in all possible
combinations without reciprocals to obtain seeds of 21 crosses. In 1994
season, three adjacent experiments were fertilized by 20,30 and 40 kg N/
fed., respectively. Each experiment, the parental inbred lines and their 21
Fl hybrids and three hybrids of sunflower (Hysun 354, G 101 and Vidoc)
were grown in a randomized complete block design with three
replications. Each plot consisted of two ridges without separation
between plots, 4 meters long and 60 em apart. Seeds were sown in hills
of25 em within ridge.
Data were recorded on seven to ten individual guarded plants
chosen at random from each plot in each fertilization experiment, except
flowering date, oil and husk percentages which were determined on the
mean plot basis. The analysis of variance was performed for the studied
traits in each experiment and then a combined analysis was carried out
whenever, homogeneity of error variance was realized. Heterosis was
computed as the percentage deviations of F1 mean performance from mid
and! or better parent also, from the yield of the three hybrids for
individual crosses. The data were genetically analyzed by the procedures
developed by Griffing (1956), Hayman (1954 a, b) and Jinks (I 954).
The results obtained can be summarized as follows:
1- Nitrogen levels mean squares were significant for all the studied
traits.
2- Significant genotype mean squares were detected for all the studied
traits in the separate nitrogen levels and their combined analysis.
Insignificant genotype x nitrogen level interaction mean squares
were obtained for all traits.
3- Mean squares for parents vs crosses were of appreciable magnitudes
in separate experiments as well as the combined data for all cases
except flowering date, plant height, number of leaves per plant and
seed yield per plant traits. ~ itsignificant interaction between
parent vs crosses andnitrogen levels meansq~ was detected for
all the studied traits. The cross (PI x P4) in the combined analysis
showed high significant heterotic effects relative to better parent for
seed yield per plant. Also the crosses (PI x p2), (PI x P4) and (PI
x P7) had significant heterotic effects relative to the better parent for
oil percentage in the combined data. Also, these crosses were the
most evident for heterosis estimates in this study for most traits. The
cross (pI x P4) significantly out-yielded by 57.03, 30.3 and 41.54 %
when compared with the three hybrids Hysun, G 101 and Vidoc,
respectively. Also, the two crosses (PI x P2) and (PI x P7)
significantly out- yielded the check hybrids Hysun by 37.72 and
35.90 %, G 101 by 14.28 and 12.77 % and Vidoc by 24.13 and
22.49 %, respectively, in the combined analysis.
4- The mean squares associated with general and specific combining
abilities were significant for all traits except number of leaves/ plant
at the 40 kg N/ fed. which showed an insignificant S.C.A. It is
evident that additive and additive by additive types of gene action
were the more important part of the total genetic variability for this
exceptional case. For other cases, both additive and non additive
genetic effects were involved in determining the performance of
single cross progeny. Also, the results revealed that all other cases
exhibited high GCA/ SCA ratios which exceeded the unity
indicating the predominance of additive and additive by additive
gene action in the inheritance of such cases. The same conclusion
was detected by genetic component analysis.
5- The mean squares of the interaction between nitrogen levels and both
types of combining ability were non significant for all traits,
revealing that additive and non additive effects were not influenced
by the environmental conditions. (nitrogen levels).
6- The parental inbred lines No. P6, P5, PI, PI, P2, PI, P2, P5, PI and
P4 appeared to be the best general combiners for number of days to
flowering, plant height, number of leaves per plant, head diameter,
1OO~seed size, number of seeds per head, IOOO~seed weight, husk
percentage, seed yield per plant and oil percentage, respectively.
7- The two crosses (pI x P4) and (pI x P7) produced the highest
desirable S.C.A effects for seed yield! plant. Also, the cross (PI x
P7) had the highest S.C.A. effects for oil percentage followed by
both crosses (PI x P6) and (PI x P2).
8- Studies on degree of dominance revealed the existence of
overdominance for flowering date, number of leaves per plant,
number of seeds per head and seed yield! plant in the three nitrogen
levels. Meanwhile, the complete dominance was present for head
diameter, and oil percentage in the three nitrogen levels and husk
percentage in the first and third nitrogen levels. The partial
dominance was detected for other cases.
9- High to moderate values for heritability in broad sense were obtained
in all traits, i.e. for number of days to flowering, number of leaves
per plant, head diameter and number of seeds per plant in the three
nitrogen levels, and 100- seed size in the first level of nitrogen,
values of heritability of narrow sense were much lower than those of
broad ones. For other cases, high heritability values in broad sense
along with moderate ones in narrow sense were detected.
10- The parental inbred lines (P6) and (P7) for flowering date and plant
height in the three nitrogen levels, (PI) for number of leaves per
plant in the three nitrogen levels and 100- seed size in the second
nitrogen level, (P7) for husk and oil percentages in the three levels
of nitrogen, (P5) for seed yield in the three nitrogen levels seemed to
be carry most of dominant genes that responsible for these traits.
However, (P5) for flowering date, number of leaves per plant; husk
percentage, and head diameter in the three nitrogen levels and
munber of seeds/ head in the second and third nitrogen levels, (PI)
for oil percentage and (P2) and (P4) for seed yield! plant in the three
nitrogen levels possessed more recessive genes for the previous
traits.
11- Significant positive correlation values were obtained between seed
yield per plant and each of plant height, number of leaves per plant,
head diameter, IOO-seed size, 1000- seed weight and number of
seeds per head in the three separate levels of nitrogen. Based on
path coefficient analysis, the most important sources of variation in
plant yield were the direct effect of 1000- seed weight and number of
seeds per head at the three nitrogen levels.