الفهرس 
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Abstract
The present study was carried out at Shandaweel Res. Station, ARC, to estimate heterosis and combining ability in grain sorghum. Seven restorer lines and seven male sterile lines were crossed to produce 49 F1 hybrids. The parents and their crosses as well as the check hybrid Sandaweel-1 were evaluated in two experiments. In the first experiment, the irrigation was normal (6 irrigations) while in the second experiment one irrigation was skipped after the first irrigation (3 irrigations). The randomized complete block design was with 3 replicates in the two experiments. Data were recorded on days to 50% flowering, plant height, panicle length and width, no. of green leaves/plant, 1000-grain weight and grain yield/plant.
The obtained data were statistically analyzed for each experiment and combined over two experiments. Also, heterosis and combining ability were estimated from line x tester analysis and the correlations among each pair of traits were estimated.
The results obtained are summarized as follows:
I- Statistical analysis and genotypes performance:
The combined analysis of variance under two irrigation treatments (normal irrigation and water stress) for all genotypes showed highly significant differences between irrigation treatments for all studied traits. Differences among genotypes were highly significant for all studied traits. The interaction between genotypes and irrigation treatments was highly significant for all studied traits. Furthermore, mean squares due crosses (C), parents (P), P vs. C, females (F), males (M), FxM and their interaction with irrigation treatments were highly significant for an studied traits except few cases.
1- Most of the F1 crosses were earlier than their early parent and thirty-eight, 23 and 15 were significantly earlier than the check Shandaweel-1 under normal, water stress and under the two irrigation treatments, respectively. The female parents ICSA-630 and ICSA-572 gave the earliest crosses compared with the other females. The male parents ICSR-102 and ICSR-31 gave the earliest crosses compared with the other male parents. It can be concluded that the average of number days to 50% flowering for all studied genotypes increased under water stress, which means that water stress delayed flowering in grain sorghum.
2-Most of the F1 crosses were taller than their parents and twenty-one, 20 and 22 crosses were highly significantly taller than the check under normal, water stress and under the two irrigation treatments, respectively. The female parents ICSA-363 and ICSA-364 and the male parents ICSR-66 and ICSR-31 gave the tallest plants when crossed with other parents. Results showed that the reduction in the average of plant height for female, male lines and F1 crosses under irrigation treatments was 14.80, 11.71, and 12.98 %, respectively.
3- Some of F1 crosses had high number of green leaves compared with their parents and the check variety. Female parents ICSA-364 and ICSA-363 gave crosses with higher number of green leaves compared with the other female parents under both irrigation treatments. The male parent and Dorado gave crosses with higher number of green leaves compared with the other male parents. The reduction in the average of Number of green leaves /plant for female, male lines and crosses under water stress condition was 26.42, 36.1 and 33.80 % respectively.
4-Most of crosses had longer panicles than their parents. Thirteen, 11and 19 crosses had significant longer panicles than the check under normal irrigation, water stress and under the two irrigation treatments, respectively. The female parents ICSA-364 and ICSA-610 gave the longest panicles when crossed with the male parents. The male parents ICSR-31 and ICSR-66 gave the longest panicles when crossed with the female parents. The reduction in the average of panicle length for female, male lines and crosses under water stress condition was 13.27, 16.34 and 12.69 % respectively.
5- Some of crosses had higher panicle width than the best parent. Most of F1crosses had smaller panicle width when compared to check. The female parents ICSA-605 and ICSA-364 and the male parents ICSR-66 and ICSR-89037 gave the widest panicles width when crossed with other parents. The reduction in the average of panicle length for female, male lines and crosses under water stress condition was 24.16, 32.77 and 35.88 % respectively.
6- Most of crosses had higher 1000- grain weight than the higher parent. Nine, 5 and 10 crosses had significant higher 1000- grain weight than the check under normal, water stress and under two irrigation treatments, respectively. The female parents ICSA-363 and ICSA-364 and the male parent ICSR-66 gave the heaviest 1000- grain weight when crossed other parents. The reduction in the average of 1000-grain weight for female, male lines and crosses under water stress condition was 12.30, 11.96 and 12.50 %, respectively.
7- Most of the F1 crosses had higher grain yield /plant than their parents. Sixteen, 11 and 16 crosses gave highly significant more than the check under normal, water stress and under two irrigation treatments, respectively. The female parents ICSA-364 and ICSA-605 and male parents ICSR-66 and ICSR-102 gave the highest yield/plant when crossed with other parents. The reduction in grain yield/plant for the female, male lines and F1 crosses under water stress condition was 31.41, 19.69 and 22.98%, respectively
8- The female parents ICSA-364, ICSA-605, and ICSA-490 and the male parent ICSR-31 showed DSI values less than one. Also, ten F1 crosses showed DSI values less than unity. The more drought tolerant crosses were (ICSA-630 x ICSR-31), (ICSA-490 x ICSR-89037) and (ICSA-572 x ICSR-102).
-II Heterosis :
1- Heterotic values for days to 50%flowering under normal irrigation ranged from -6.54 to 18.48%, twelve crosses had negative and highly significant heterosis. Under water stress ranged from -6.80 to 19.14%, seven crosses had negative and significant heterosis. The F1 crosses (ICSA-364 x ICSR-89035), (ICSA-572 X ICSR-31), (ICSA-572 X ICSR-102),(ICSA-572 X ICSR-89035) and (ICSA-572X ICSR-89035) showed the highest negative values of heterosis over the best parent under both irrigation treatments.
2- Heterotic values for plant height under normal irrigation ranged from -38.79 to 67.83%, twenty-five crosses had positive and highly significant heterosis. Under water stress ranged from -45.00 to 83.5%, twenty-seven crosses had positive and significant heterosis.
3- Heterotic values of number of green leaves under normal irrigation ranged from -43.33 to 57.14%, eighteen crosses had positive and highly significant heterosis. Under water stress it ranged from -45.45 to 78.57%, nine crosses had positive and highly significant heterosis.
4- Heterotic values of panicle length under normal irrigation ranged from -16.78 to 26.97%, seventeen crosses had positive and significant heterosis. Under water stress it ranged from -25.79 to 42.48%, seventeen crosses had positive and significant heterosis.
5- Heterotic values of panicle width under normal irrigation ranged from -27.27 to 36.36%, eleven crosses had positive and highly significant heterosis. Under water stress it ranged from -27.22 to 48.33%, twenty-one crosses had positive and highly significant heterosis.
6- Heterotic values of 1000- grain weight under normal irrigation ranged from -29.61 to 23.04%, twelve crosses had positive and highly significant heterosis. Under water stress it ranged from -27.81 to 15.98%, ten crosses had positive and highly significant heterosis. The F1 crosses (ICSA-364 x ICSR-102), (ICSA-605 x ICSR-66), (ICSA-605 x ICSR-102), (ICSA-605 x ICSR-89037) and (ICSA-630 x ICSR-31).gave positive and highly significant heterotic values for 1000-grain weight compared with the best parent.
7- Heterotic values of grain yield/ plant under normal irrigation ranged from -65.93 to 65.45%, fifteen crosses had positive and significant heterosis. Under water stress it ranged from -62.88 to 68.81%, twenty-six crosses had positive and significant heterosis. The F1 crosses, (ICSA-363 x Dorado), (ICSA-572 x Dorado), (ICSA-605 x ICSR-31), (ICSA-605 x ICSR-102), (ICSA-610 x ICSR- 31) and (ICSA-610 x Dorado) gave the highest heterosis values over the best parent under both irrigation treatments.
III- Combining ability:
III-1- General combining ability:
1- The male line ICSA-364 was a good combiner for all studied traits except earliness.
2- The female lines IcSA-363, ICSA-572 and ICSA-630 and the male lines ICSR-31, ICSR-59 and ICSR-102 are good combiners for earliness.
3- The female lines ICSA-363 was a good combiner for no. of green leaves, 1000-kernel weight and grain yield/plant.
4- The female line ICSA-605 was a good combiner for panicle width, grain yield and intermediate plant height.
5- The two male lines ICSR-31 and ICSR-66 are good combiners for most studied traits except few cases.
III-2- Specific combining ability (SCA)
1-crosses no. 15, 17 and 49 had negative and highly significant SCA effects for days to 50 % flowering under both irrigation treatments, indicating that these crosses would be considered good combinations for earliness.
2- Crosses no. 4, 8, 9, 17, 19, 21, 22, 23, 33, 36, 41, 44 and 49 were considered as good combiners for tallness under both irrigation treatments. While the crosses number 11, 15, 30 and 31 were considered to be the best combination for shortness
3- Crosses no. 28 and 40 had positive and significant SCA effects under both irrigation treatments for no. of green leaves/plant.
4-Specifice combining ability under both irrigation treatments showed that the crosses number 25, 33 and 48 had positive and significant SCA effect for panicle length.
5-The cross (ICSA-490 x ICSR-89035) was considered good combination for increasing panicle width under both irrigation treatments.
6-The crosses number 16, 28, 32, 33, 40 and 48 were considered the best combination for increasing the 1000-grain weight under both irrigation treatments.
7-The crosses no. 5, 6, 12, 17, 22, 28, 36, 43 and 48 had positive and significantly SCA effects for grain yield/plant under both irrigation treatments. The crosses (ICSA-610 X ICSR-31), (ICSA-572 x ICSR-89035) and (ICSA-572 x ICSR-31) were considered the good combination for grain yield/ plant under both irrigation treatments.
IV- Phenotypic correlation:
The correlation between grain yield/ plant and each of plant height, panicle width, number of green leaves/ plant and 1000- grain weight was positive and highly significant, while it was positive and insignificant with days to 50% flowering and panicle length.