الفهرس 
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Abstract
This study was carried out during the summer seasons of 2020 and 2021 at Agricultural Research Farm, Faculty of Agriculture, New valley University to study the general and specific combining ability and the relationships among the grain yield and its attributes for 81 S1 lines derived from two sources i.e., IY-148 and Mallawy-121, which were obtained from National Maize Research Program (NMRP), Field Crops Research Institute, Agric. Res. Centre (ARC).
In 2020 season top crosses were formed in three isolated blocks for 81 S1 lines using three testers i.e., SC168, TWC370 and IY335 at Agricultural Research Farm, Faculty of Agriculture, New valley University.
In 2021 season 243 top crosses with their parents (81 S1 lines and the three testers) were evaluated at Agricultural Research Farm, Faculty of Agriculture, New valley University, in a Randomized Complete Block Design (RCBD) with three replications. Experimental plot size was one row, 4 meters long and 70 cm apart and 25 cm between hills within row (2.8m2). Seedlings were thinned to one plant/hill before the first irrigation (three weeks after sowing). Fertilizer was applied at the rate of 120 kg nitrogen/Fad. in three doses. Normal cultural practices were applied as recommended in sandy soil as in the new valley.
The obtained results could be summarized as following:
The partitioning of summation of square for crosses to lines (L), testers (T) and L vs. T revealed highly significant differences among each of crosses, lines, testers and their interaction for all studied traits i.e., plant height, ear height, days to 50% silking, grain yield/plot, ear length, ear diameter, no. of rows/ear, no. of kernels/row, and 100-kernels weight.
The greater contributions of L vs. T interaction than both of lines and testers indicates higher estimates of variance due to specific combining ability for traits i.e., number of kernels/row, 100-kernel weight, and days to 50% silking. Otherwise, the greater contributions of lines than both of testers and L vs. T interaction indicates higher estimates of variance due to general combining ability and predominant of lines influence for traits i.e., ear length, ear diameter, number of rows/ear, plant height, ear height and grain yield/plot.
These results possessed different genetic performance for the studied traits of the current S1 lines. Thirty-five S1 lines surpassed their general mean of lines in range of 0.59 to 244.88 with an average of 62.86% for grain yield/plot. Out of them, the superior fourteen S1 lines exceeded the general mean of lines in range of 48.49 to 244.88 with an average of 99.74% for grain yield/plot.
The remarkable results that the SCI 168 (T1) ranked in the first order among the testers for ear height, days to 50% silking and grain yield/plot and surpassed their general mean by 11.78, 3.47 and 71.30%, respectively. Moreover, the TWC 370 (T2) was the longest tester and exceeded the general mean by 6.58%. Otherwise, the IY 335 (T3) was the poorest tester for the previous four traits.
The mean of 243 S1 top crosses ranged from 91.67 (L1T1) to 182.17 (L10T3) with an average of 138.82 cm, 41.33 (L63T2) to 110.5 (L36T1) with an average of 78.96 cm, 5.67 (L59T2) to 20.17 (L52T2) with an average of 15.64 cm, 2.67 (L59T2) to 5.50 (L29T1) with an average of 4.61 cm, 9.33 (L22T2) to 18.33 (L36T1) with an average of 14.72, 8.33 (L56T3) to 40.67 (L33T2) with an average of 27.76, 33.00 (L56T2) to 75.00 (L64T1) with an average of 66.66 day, 16.10 (L56T3) to 47.98 (L74T2) with an average of 35.64 g and 0.03 (L56T3) to 1.37 (L29T2) with an average of 0.61 kg for plant height, ear height, ear length, ear diameter, no. of rows/ear, no. of kernels/row, days to 50% silking, 100-kernels weight and grain yield/plot, respectively. These results exerted different genetic behavior of the obtained S1 top crosses for all studied traits.
Superior thirty-four S1 top crosses surpassed their general mean of 243 S1 top crosses by more than 50% comparing to its value with range of 50.82 to 124.59 with an average of 82.59% for grain yield/plot. Those superior S1 top crosses were divided into three groups as a- 16 S1 top crosses were derived from T1 and exceeded the general mean in range of 50.52 to 116.39 with an average of 78.07%; b- 17 S1 top crosses were derived from T2 and surpassed the general mean in range of 60.66 to 124.59 with an average of 88.33%; and c- one cross was derived from T3 and exceeded the general mean by 57.38% for grain yield/plot. It is clear result that the average (88.33%) of S1 top crosses derived from the T2 was in the first order followed by S1 top crosses (78.07%) derived from T1 and T3 came in the last order. The obtained results indicating that the T2 could be used as tester to mate the maize under New Valley climate conditions.
The mean of S1 top crosses were in different response according to the involved S1 lines, which ranged from 0.21 (L56) to 1.07 (L29) with an average of 0.61 over the three testers for grain yield/plot. The best ten S1 lines for grain yield/plot in ranking, which enhanced their S1 top crosses over the three testers were L29 (75.41); L26 (72.13); L17 (70.49); L74 (70.49); L5 (59.02); L33 (55.74); L20 (54.10); L25 (54.10); L30 (50.82) and L18 (47.54%) comparing to the general mean of S1 top crosses.
The preferable combinations among the superiority of both S1 lines and tester to mate together were the following S1 top crosses in ranking with T1 as L29T1 (93.44); L18T1 (91.80); L26T1 (91.80); L30T1 (91.80); L5T1 (75.41); L17T1 (67.21); and L74T1 (67.21), and with T2 as L29T2 (124.59); L17T2 (113.11); L74T2 (111.48); L33T2 (88.52); L25T2 (85.25); L18T2 (81.97); and L20T2 (80.33). It is being noted that the S1 lines i.e., L29, L17, L74 and L18, in ranking, shared both of T1 and T2 in different crosses.
The obtained results for S1 top crosses possessed different genetic make-up and explained the significant mean square of line x tester analysis for current S1 top-crosses, their parents i.e., lines and testers as well as their interaction for all studied traits.
The values of GCA effects of S1 lines ranged from -0.403** to 0.460** for grain yield/plot. Out of current 80 S1 lines, twenty-two S1 lines possessed positive and significant or highly significant GCA effects.
Concerning the testers, T2 was the best combiner, which possessed positive and highly significant GCA effect of (0.114**), followed by T1 (0.030*). Otherwise, T3 was the poorest with undesirable GCA effect of (-0.144**) for grain yield/plot.
The genetic behavior of GCA effects for S1 lines and testers were differed among the other studied traits.
The values of SCA effects of 243 S1 top crosses ranged from (-0.464** to 0.697**) for grain yield/plot. Fourteen S1 top crosses possessed positive and significant or highly significant SCA effects. The best ten S1 top crosses for SCA in ranking were L11T1 (0.697**), L77T1 (0.405**), L10T3 (0.390**), L35T2 (0.370**), L6T1 (0.357**), L2T3 (0.350**), L62T2 (0.337**), L27T2 (0.329**), L39T1 (0.318**) and L71T1 (0.317**). It is clearly results that T1 involved in half of these top top-crosses, followed by T2, indicating to their good specific combiners with shared S1 lines to inherit their genetic make-up into the current crosses. This finding is in accordance with the GCA effects of T1 and T2, but not for S1 lines, because the best ten S1 lines for GCA did not involve in the top ten crosses for grain yield/plot.
The genetic behavior of SCA effects for the S1 top crosses were varied among the other studied traits.
It remarkable results that the specific combining ability variance (σ2SCA) was more important than the general combining ability (σ2GCA) for all studied traits in current crosses of maize, revealing the preponderance of dominance variance in controlling the studied traits. These finds are in line with the variances of additive (σ2A) and non-additive (σ2D), where the dominance gene action was more importance in inheritance of these traits. Moreover, the estimates of combining ability ratio (CAR) were much lower than unity, indicating the preponderance of dominance variance in controlling these traits. In accordance results, the ratios of σ2GCA/ σ2SCA and (σ2D/σ2A)1/2 were expressing this situation of inheritance monitor of dominance, were the first one was very less (0.0016-0.0096) and the last one recorded very high values than unity (7.33-17.74) for all studied traits. Finally, the narrow sense heritability (Hn) exhibited very low values ranged from 0.26 (days to 50% silking) to 1.64 (grain yield/plot), and it’s coupled the same trend of non-additive and resembled that the dominance was the most likely to inherit the studied trait in the current crosses of maize. In the same context, the broad sense heritability possessed high values which ranged from 80.57 (days to 50% silking) to 98.64% (grain yield/plot), giving enough genetic variance for future improvement depending on non-additive behavior due to the less additive one for all studied in the current crosses of maize.
Concerning the correlation coefficient for S1 top-crosses, strong positive and significant or highly significant values were recorded and in arraying from 0.136* to 0.824** among all studied traits, except number of rows/ear with 100-kernels weight was not significant. The highest value of 0.824 was exerted between plant height and ear height, maybe due to the same genes controlled the height even for plant or ear. Moreover, the trend of positive and highly significant correlation estimates were recorded between grain yield/plot and other traits in ranking i.e., number of kernels/row, ear diameter, ear length, number of rows/ear, plant height, ear height, and 100-kernels weight. The obtained data expressed the strong and positive relationship for the genetic make-up in the inheritance of these traits inside the genome of the current new S1 top crosses of maize. Consequently, the selection program for grain yield should take importance for these traits especially number of kernels/row and ear diameter which recorded the highest correlation values with grain yield. Moreover, the selection for the previous traits individually or simultaneously should be expressed to increase the yielding ability.
Conversely to the previous results, days to 50% silking was possessed strong negative and significant or highly significant estimates with all other studied traits.
The stepwise regression analysis for dependent trait of grain yield/plot (GYP) was expressed three fitted models i.e., model 1 has only one independent trait of number of kernels/row (NKR) which gave R2 = 0.565, model 2 has two independent traits of number of kernels/row (NKR) and ear diameter (ED) with R2 = 0.613, and model 3 has three traits of number of kernels/row (NKR), ear diameter (ED) and days to 50% silking (SILK) with R2 = 0.626.
The stepwise regression revealed that the contributions of number of kernels/row and ear diameter were powerful in grain yield/plot of maize as outlined with R2 = 0.613 in model 2. This results are in line with the strong positive correlation estimates between grain yield/plot and both of number of kernels/row and ear diameter. Consequently, number of kernels/row and ear diameter should take remarkable importance and great place through the selection program for grain yield in maize.
The expected grain yield/plot for the obtained fitted stepwise models were insignificant difference comparing to the actual grain yield/plot into the three fitted models as revealed by values of t-test less than unity in all models. Moreover, the estimates of correlation coefficients between expected and actual grain yield/plot were positive and very high. These results displayed the effeteness of stepwise regression analysis to determine the strongest trait/s through their genetic contribution into high grain yield of maize.
The results of path-analysis illustrated that the number of kernels/row and ear diameter exhibited the highest positive direct effect on grain yield/plot. All others direct effects which were exerted from other variables were negative and neglected values on grain yield/plot. Moreover, the positive indirect effects on grain yield/plot were correlated in ranking with number of kernels/row and ear diameter across other variables. The values of indirect effect of number of kernels/row and ear diameter were positive via all traits, except days to 50% silking was in negative values. The obtained results of current path-analysis confirmed the previous findings of correlation and stepwise regression analyses that both of number of kernels/row and ear diameter should take importance as selection criteria in improvement program of maize.