الفهرس 
Introduction
The performance of traits under heat stressOnly 14 pages are availabe for public view
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Abstract
This study was conducted at Assiut Agricultural Research Station, ARC; Egypt during the three growing seasons 2007/08, 2008/09 and 2009/2010. The genetic materials chosen to be used in this study as parents included eight durum wheat cultivars, which represents a wide range of diversity for several traits. Also, to study the genetic analysis of yield and its components of 8-parents diallel (excluding reciprocals) crosses in both F1’s and F2-populations under recommended and late planting dates. Each experiment was designed in a randomized complete block design with three replications.
Results obtained will be summarized as follows:
1. Analysis of variance
• Mean squares due to genotypes, parents and crosses were highly significant for all studied characters for F1 and F2 under both planting dates i.e. days to heading and maturity, plant height, spike length, flag leaf area, biological yield/plant, grain yield/plant, no of kernel/spike and 100-kernels weight. Also, highly significant recorded for mean squares due to no. of spike/plant, except mean squares due to crosses for F1 under late planting date. Same trend was found for harvest Index, except mean squares due to genotypes (G), parents (P) and crosses (C) for F1 and F2 under late planting date.
• Mean squares due to P vs. C were highly significant for all studied traits, except for F1 of no. of spike/plant, number of kernel/spike and harvest index under normal planting date and grain yield under late planting date.
• Mean squares due to GCA were highly significant for all studied characters for F1 and F2 under both planting dates, except for F1 of harvest index under late planting date.
• Mean squares due to SCA for F1 and F2 over the two planting dates were highly significant for all studied traits, except F1 mean squares due to biological yield/plant under late planting date and grain yield and harvest index under late planting date.
• Mean squares due to GCA/SCA ratios in F1 and F2, plant height, biological yield/plant, grain yield/plant and number of kernel/spike under both planting dates possessed higher value of GCA/SCA ratios comparing with other studied traits.
2. Performance of genotypes
Stress conditions (late planting date) reduced number of days to heading and maturity, flag leaf area, plant height, spike length, no. of spike/plant, no. of kernel/spike, 100-kernels weight, biological yield/plant, harvest index and grain yield/plant as compared with non-stress condition (recommended planting date).
The reduction values could be summarized as follows:
• Stress conditions reduced days to heading by 13.52 and 11.46 % over all genotypes when compared with recommended date for F1 and F2, respectively.
• The reductions in days to maturity time were 13.84 and 12.81 % for F1 and F2, respectively.
• Plant height decreased by 12.41 and 11.70 % for F1 and F2, respectively.
• The reduction percentages in spikes/plant were 24.39 and 51.43 % for F1 and F2, respectively.
• The reductions in spike length over all genotypes under late planting were 12.42 and 9.01 % for F1 and F2, respectively.
• The reduction values in flag leaf area over all genotypes under late planting were 30.07 and 31.59% for F1 and F2, respectively.
• The decreasing percentage in biological yield/plant over all genotypes under late planting was 26.96 and 14.96 % for F1 and F2, respectively.
• The reduction percentage in grain yield/plant over all genotypes under late planting was 32.30 and 18.85 % for F1 and F2, respectively.
• Number of kernel/spike decreased over all genotypes under late planting by 12.25 and 14.00 % for F1 and F2, respectively.
• The reduction values in 100-kernal weight over all genotypes under late planting were 23.31 and 22.65 % for F1 and F2, respectively.
• Late planting date reduced harvest index by 8.34 and 4.87% in F1 and F2, respectively comparing to recommended planting date.
3. General and Specific combining ability effects:
1. General combining ability for days to heading of F1 and F2 revealed that the parents of P1, P2, P6 and P7 could be considered good combiners under both normal and late planting dates. SCA effects of F1 and F2 for some crosses (P1 × P8, P2 × P8, P3 × P6, P3 × P8, P4 × P8, P5 × P8, 7 and P6 × P8) had negative and highly significant under both normal and late planting dates. They could be considered for breeding program for improvement of earliness in wheat.
2. GCA for days to maturity of F1 and F2 for parents P2, P3 and P7 were considered to be a good combiners under both normal and late planting dates. SCA effects for days to maturity in F1 crosses P2 × P5, P3 × P5, P3 × P6, P3 × P8, P4 × P5, P4 × P6, P4 × P7 and P6 × P7 showed negative and significant or highly significant under normal and late planting dates. Moreover, SCA effects for days to maturity of F2 population such as P3 × P4, P3 × P5, P3 × P6, P3 × P7 and P6 × P8 showed negative and significant or highly significant under normal and late planting dates.
3. The good combiner for plant height was P8 in F1 and F2 under normal and late planting dates. For SCA, the F1 crosses P1 × P8 and P6 × P8 showed positive and significant or highly significant under normal and late planting dates. Most of SCA in F2 populations showed negative effects under both planting dates.
4. The parental genotypes for number of spikes/plant of P4 and P7 showed highly significant GCA effects in F1 and F2 under normal and late planting dates. Also, SCA effects for number of spikes/plant proved that P6 × P8 cross had highly significant in F1 and F2 under normal planting date. Meanwhile, P3 × P6 showed significant and positive SCA in F1 and F2 under late planting date.
5. GCA for spike length of F1 and F2 parental genotypes of P1, P2 and P8, except P1 for F2 under late planting date, were considered good combiners under both normal and late planting dates. In addition to, SCA for spike length of F1 crosses P1 × P6, P1 × P7, P2 × P8, P3 × P4 and P6 × P8 and F2 population P1 × P8, P3 × P4 and P7 × P8) showed positive significant and highly significant under normal and late planting dates.
6. GCA effects of parental P1 and P2 were considered to be good combiners for flag leaf area under both normal and late planting dates except P2 for F2 under late planting date. SCA effects of F1 crosses P3×P6, P3 × P7 and P5 × P8 and SCA effects of F2 population P1 × P7 and P5 × P8 showed positive and significant or highly significant SCA effects under normal and late planting dates.
7. GCA of parental genotypes P2, P4 and P7 were revealed to be good combiners for grain yield under both normal and late planting dates, except P2 for F2 under late planting date. The best hybrids of F1 crosses displayed positive and significant or highly significant SCA effects for grain yield were P1 × P4, P1 × P6, P4 × P7 and P6 × P8 under normal planting date. Meanwhile, the hybrid P2 ×P4 showed significant and positive SCA estimates under late planting date. Other hybrids showed negative effects under late planting date.
8. General combining ability effects of F1 and F2 for biological yield were positive and highly significant for P4 and P7 under both normal and late planting dates. Therefore, they could be considered good combiners for biological yield. While, P2 showed the same trend, except under late planting date. The best hybrids displayed positive and significant or highly significant SCA effects of F1 for biological yield were P1 × P4, P1 × P6, P2 × P7, P4 × P7 and P6 × P8 under normal planting date. Meanwhile, the hybrid P2 × P4 showed significant and positive SCA estimates under late planting date. SCA effects of F2 population showed that P2 × P6 and P4 × P8 had positive and significant SCA effects under late planting date. Most population has negative effects under normal planting date.
9. General combining ability effects of F1 and F2 for number kernel/plant were positive and significant and highly significant for P2, P4 and P7 under normal and late planting dates. Therefore, they could express to be good combiners for number of kernel/spike. Cross P3 × P4 had positive and highly significant SCA effects in F1 and F2 under normal and late planting dates.
10. Under F1 and F2 parent (P5) was considered good combiner for 100- kernel weight under both planting dates. Five F1 crosses i.e. P1 × P8, P2 × P8, P3 × P8, P5 × P8 and P6 × P7 showed positive and significant or highly significant SCA effects for 100-Kernel weight under both normal and late planting dates. Under F1 and F2, one cross (P3 × P8) had positive and highly significant SCA effects for 100-Kernel weight under both planting dates.
11. General combining ability effects showed positive and significant and highly significant for P5 and P3 of F1 and F2 under both planting dates, respectively. Therefore, they could be considered good combiners for harvest index. SCA effects for harvest index of F1 revealed that four crosses of P1 × P2, P3 × P6, P5 × P7 and P7 × P8 were the best hybrids displayed positive and significant or highly significant under normal planting date. Meanwhile, the most hybrids showed negative and insignificant SCA estimates under late planting date. SCA effects for harvest index in F2 expressed that P2 × P4, P4 × P6 and P6 × P7 showed positive and significant under normal planting date. While, most hybrids showed negative effects under late planting date.
4. Heterosis
1. Days to heading
The heterosis effects relative to mid and better parents for days to heading were significant and negative (earlier) in some crosses and vice-versa for others. It ranged from -0.559 (P4 × P7) to -9.034 % (P6 × P8) and from -2.198 (P4 × P6) to -2.273 % (P3 × P6) over MP and BP, respectively.
Same trend could be found for heterotic values under late planting date, which ranged from -13.947 (P3 × P6) to -13.415 (P6 × P7) and from -3.896 (P1 × P6) to -5.333 (P6 × P7) over MP and BP, respectively.
2. Days to maturity
Nine and Five crosses possessed negative and significant heterotic values over MP and BP under recommended planting date, respectively. These values ranged from -2.190 (P3 × P8) to -6.227 (P4 × P6) and from -2.030 (P3 × P5) to -5.185 (P4 × P6), respectively.
Same trend recorded under late planting date and ranged from -1.841 (P7 × P8) to - 6.195 (P4 × P7) over MP and BP, respectively. It is clear results that the crosses of P3×P5, P4×P6 and P4×P7 showed negative and significant values of heterosis over MP and BP under both planting dates for days to maturity.
3. Plant height
Positive and significant or highly significant heterotic values were found for eighteen and four hybrids over MP and BP under normal planting date, respectively. It ranged from 3.919 (P2 × P6) to 9.775 (P1 × P8) and from 4.542 (P4 × P5) to 5.176 % (P3 × P7) over MP and BP, respectively.
Same response could be fond for twenty one heterotic values under late planting date, which ranged from 3.258 (P5 × P7) to 12.049 (P2 × P3) over MP. Moreover twelve crosses varied from 2.759 (P1 × P4) to 7.888% (P2 × P3) up to BP. The cross P1 × P3 has positive and significant values of heterosis over MP and BP under recommended and late planting dates.
4. Number of spikes/ plant
Positive and significant or highly significant heterotic values were found for all crosses (twenty eight) and twenty one crosses over MP and BP under normal planting date, respectively. It ranged from 2.142 (P2 × P5) to 23.544 (P1 × P6) and from 0.921 (P6 × P8) to 17.984 % (P1 × P6) over MP and BP, respectively.
Only there are ten and eight crosses showed positive and highly significant heterotic values over the MP and BP under the late planting date, which ranged from 2.364 (P4 × P6) to 16.972 (P6 × P7) and from 2.113 (P2 × P5) to 16.555 (P6 × P7) over MP and BP, respectively.
5. Spike length
Positive and highly significant heterotic values were found for twenty six and twenty one hybrids over MP and BP under normal planting date, respectively. It ranged from 1.540 (P4 × P5) to 15.222 (P1 × P8) and from 1.083 (P2 × P7) to 13.398 % (P2 × P8) over MP and BP, respectively.
Moreover, twenty six and nineteen crosses possessed same trend and ranged from 0.834 (P2 × P3) to 12.345 (P2 × P8) and from 0.866 (P3 × P8) to 10.345 % (P3 × P4) over MP and BP under late planting date, respectively
6. Flag leaf area
Twenty three and eighteen positive and highly significant heterotic values were found over MP and BP under normal planting date, respectively. It ranged from 4.983 (P2 × P4) to 32.862 (P1 × P8) and from 3.004 (P1 × P6) to 22.646 % (P3 × P8) over MP and BP, respectively.
Also, heterotic values under late planting date were positive and highly significant for twenty five and eleven crosses over MP and BP, respectively, and varied from 2.241 ( P5 × P7) to 24.659 (P3 × P6) and from 3.242 (P1 × P5) to 21.597 % (P3 × P6) over MP and BP, respectively.
7. Grain yield/plant
Under normal planting date, positive significant or highly significant heterosis was found for twenty and seven hybrids over MP and BP and ranged from 3.829 (P3 × P7) to 55.491 (P1 × P6) and from 8.798 (P4 × P7) to 41.122 % (P1 × P6), respectively.
Moreover, estimates of heterosis under late planting date showed positive significant or highly significant heterosis for eleven and three hybrids over MP and BP and varied from 5.704 (P5 × P6) to 17.980 (P2 × P4) and from 4.297 (P2 × P7) to 11.532 % (P2 × P4) over MP and BP, respectively.
The highest positive heterosis over MP was recorded for the hybrids P1 × P6, P6 × P8, P1 × P4, P3 × P6, P1 × P8, P1 × P2, P2 × P7, P2 × P8, P2 × P3, P4 × P7, P3 × P8, P1 × P3, P2 × P8, P2 × P4, and P1 × P5 under the normal planting date and P2 × P4 under both planting dates.
The hybrids P2 x P7 and P4 x P7 exhibited sizeable and positive significant heterosis over MP and BP under both of normal late planting dates.
8. Biological yield/plant
Positive and significant or highly significant heterotic values were found for six and one hybrids over MP and BP under normal date, respectively. It ranged from 9.587 (P1 × P8) to 30.965 for cross (P1 × P6) over MP.
Same trend heterotic values under late planting date were positive and highly significant for five and one crosses over MP and BP, respectively. It ranged from 9.932 (P3 × P6) to 22.718% (P7 × P8) over MP.
9. Number of kernel/spike
Two hybrids (P1 × P3 and P3 × P4) possessed positive and highly significant heterotic values over MP under normal planting date. Their values were 11.445 and 17.488 %, respectively. Otherwise, there is no crosses has positive value over better parent.
Thirteen and three heterotic values under late planting date were positive and significant or highly significant over MP and BP and varied from 6.861 (P3 × P8) to 24.147 (P6 × P8) and from 7.273 (P6 × P8) to 10.803 % (P2 × P6) over Mp and BP, respectively.
10. 100-kernel weight
Under normal planting date, positive significant or highly significant heterosis was found for ten and four hybrids over MP and BP, respectively. It ranged from 6.349 (P2 × P4) to 25.765 (P1 × P8) and from 9.456 (P7 × P8) to 10.621 % (P1 × P8), respectively.
Same view was found under late planting date for fifteen and nine hybrids over MP and BP, respectively. It varied from 7.816 (P2 × P3) to 24.777 (P1 × P8) and from 7.675 (P1 × P6) to 19.946 % (P1 × P8) over MP and BP, respectively.
11. Harvest Index
Positive and significant or highly significant heterotic values were found for twenty five and twenty hydrids over MP and BP under normal planting date, respectively. It varied from 5.735 (P6 × P7) to 34.047 (P1 × P2) and from 6.046 (P2 × P6) to 28.494 % (P5 × P7), respectively.
Moreover, four and three heterotic values under late planting date were expressed same trend and ranged from 11.369 (P4 × P6) to 25.710 (P6 × P8) over MP and from 8.988 (P1 × P5) to 25.283 % (P6 × P8) over BP.
5. Heat susceptibility index and sensitivity
The results indicated that six parental genotypes i.e. P1, P2, P3, P4, P5 and P6 showed heat susceptibility index (HSI) of 0.712, 0.937, 0.281, 0.428, 0.923 and 0.342, respectively. These genotypes could be considered average susceptible to heat. One of them, P3 was less sensitive to heat.
Regarding F1-hybrids, the results indicated that thirteen hybrids i.e. P1×P8, P2×P4, P2×P5, P2×P6, P3×P4, P3×P7, P3×P8, P4×P5, P4×P7, P4×P8, P5×P8, P6×P7 and P7×P8 showed heat susceptibility index (DSI) of less than one. These genotypes could be considered average susceptible to heat. Twelve of them, P1×P8, P2×P4, P2×P5, P2×P6, P3×P4, P3×P7, P3×P8, P4×P5, P4×P8, P5×P8, P6×P7 and P7×P8 were less sensitive to heat. On the other hand, all F1-hybrids were less sensitive to heat (less than one), except eleven hybrids i.e. P1×P4, P1×P6, P2×P3, P2×P7, P2×P8, P3×P5, P3×P6, P4×P6, P5×P6, P5×P7 and P6×P8 were average sensitive to drought.
In the F2-populations, seventeen populations i.e. P1×P2, P1×P3, P1×P4, P1×P5, P1×P6, P1×P7, P2×P4, P2×P6, P2×P7, P3×P4, P3×P5, P3×P7, P4×P5, P4×P7, P4×P8, P5×P7, and P7×P8 showed heat susceptibility index (HSI) of less than one (less susceptible) and (less sensitive) in sensitivity test in the recommended planting date. On the other hand, eight F2-populations were less sensitive to heat (less than one) i.e. P1×P4, P1×P5, P1×P7, P3×P4, P3×P7, P4×P5, P4×P8 and P5×P7 showed heat susceptibility index (HSI) of 0.50, 0.89, 0.65, 0.59, 0.23, 0.95, 0.65 and 0.57 under late planting date, respectively.
In general, P3 and three hybrids i.e. P3×P4, P3×P7 and P4×P8 in F1 and F2 generations gave drought susceptibility index less than one (less susceptible), gave also values less than one (less sensitive) in sensitivity test.
6. Correlation coefficient
In the present study correlation coefficients among the various paris of all studied traits were calculated using the data of F1 and F2 progenies in the normal and late planting dates.
Days to heating was positively correlated with days of maturity and plant height under normal and late planting dates. Moreover, the correlation coefficients recorded higher value in late comparing to recommended planting date.
Days to maturity was positively correlated with days of heating, plant height, number of spike/plant and spike length. Otherwise, the negative values were recorded with number of kernel/plant and revealed higher trend under late planting date.
Plant height was positively correlated with days of heating, days of maturity, number of spike/plant and spike length. But, the negative values recorded with number of kernels/plant and harvest index.
Number of spike/plant was positively correlated with grain yield/plant, biological yield and number of kernel/plant under recommended planting date and grain yield under late planting date.
Spike length was positively correlated with flag leaf area under both of planting dates. Otherwise, negative values exhibited with harvest index under also both of planting dates.
Flag leaf area was positively correlated with 100 kernel weight under recommended and biological and grain yield/plant under late planting date.
Biological yield/plant was positively correlated with grain yield/plant and number of kernel/plant under both of recommended and late planting dates. Moreover, it was negatively correlated with harvest index under both planting dates.
Number of kernel/plant was negatively correlated with 100-kernel weight under both of planting dates.
Moreover, positive correlation values was observed between grain yield per plant and each of number of spike plant, biological yield/plant and number of kernel/plant under both recommended and late planting dates. Consequently, the selection for these traits will be more efficient to increase the grain yield under both of planting dates especially under late one, which matched the best tolerance.