In 2007, five maize inbred lines were crossed in all possible combinations without reciprocals by using a half diallel crosses mating design to obtain 10 single cross. Inbred parents and their F1 single crosses were evaluated through 2008 season to evaluate the role of general and specific combining ability and heterosis for some agronomic traits. Results indicated that mean squares of genotypes were highly significant for all studied traits, i.e., ear diameter, ear length, number of kernels/row, 100-kernel weight, ear yield per plant, grain yield per plant and shelling percentage. General Combining Ability (GCA) and Specific Combining Ability (SCA) mean squares were highly significant for all studied traits. The GCA/SCA ratio was less than unity for all studied traits; this means that these traits are predominantly controlled by non-additive gene action. Significant positive GCA effects were found for all studied traits. Based on GCA estimates, it could be concluded that the best combiners were Rg5 and Rg8 inbred lines for most of studied traits. This result indicated that these inbred lines could be considered as good combiners for improving these traits. Significant positive SCA effects were found for all studied traits. Based on SCA effects, it could be concluded that the best crosses for ear diameter and 100-kernels weigh was G507AxG516; for ear length was G516xRg8; for kernels number/row was G516xG278; for ear yield/plant, grain yield/plant and Shelling percentage was G278xRg5. These crosses could be selected and used in breeding programs for improving these traits. Results showed positive significant heterosis values for all studied traits. The best crosses over both their mid-parents and better-parents for ear diameter and 100-kernel weigh was G507AxG516; for ear length and kernels number/row was G516xG278; for ear yield/plant and grain yield/plant was G278xRg8 and for Shelling percentage was G278xRg5.

Six populations; P1, P2, F1, F2, BC1 and BC2 of four bread wheat crosses were used in this study to determine quantitative genetic parameters for yield and its components characters under normal and water stress treatments. The means of the six generations were recorded for plant height, spikes number plant-1 , grains number spike-1 , 100-grain weight and grain yield plant-1 in four crosses namely; Line 1 × Sakha 93, Line 1×Sakha 94 , Sakha 93×Gemmiza 9 and Sakha 94 × Gemmiza 9 generated from four diverse parents. The experiment was carried out in 2006/2007 to 2008/2009 seasons at Sakha Agric. Res. Station, ARC. The means of the four crosses significantly decreased under the water stress treatments for yield and its components characters as the effect of water stress at most cases. The T-test of differences between parents of each cross under each treatment showed highly significant values in most cases in the four studied crosses under both treatments. The results showed the importance of additive gene effects in the inheritance of plant height and spikes number plant-1 , while, additive, dominance and epistasis were the important in the inheritance of grains number spike-1 , 100-grain weight and grain yield plant-1 at most cases under both normal and water stress treatments. Moreover, additive genetic variance played the greatest and the important role in the inheritance of plant height, spikes number plant-1 and grain yield plant-1 at most cases under both water treatments. On the other hand, dominance genetic variance was the greatest and the important in the inheritance of grains number spike-1 and 100-grain weight at most cases under both water treatments. On the other side, heritability in broad sense had medium to high percentages for all studied characters at all cases under normal and water stress treatments. Meanwhile, heritability in narrow sense had moderate to high values for yield and yield components characters at most cases under both water treatments, except grains number spike-1 which had low values at most cases under both water treatments. Genetic advance under selection was low for plant height at most cases under both water treatments. While, it was high for spikes number plant-1 and grain yield plant-1 at most cases under both water treatments. Also, it was founded to be low to high for plant height, grains number spike-1 and 100-grain weight at most cases under both water treatments.

Two field experiments were conducted out during 2012 and 2013 seasons to estimate combining ability, heterosis for six inbred lines (Three American inbreds: P97, B73and Oh.43 and three Egyptian inbred lines: R39, Inb.1021 and Inb.1004) and its F1 crosses. The most important results obtained from this investigation can be summarized as follows:  The differences among means of parental inbreds and also among means of crosses were significant or highly significant for all studied traits.  Mean squares of crosses were highly significant for all studied traits, indicating wide range of genetic variability among the studied crosses and this is primary requirement for further computation.  Both general and specific combining abilities mean squares were found to be highly significant for all studied traits.  GCA/SCA variances ratios were found to be lower than unity for six traits i.e. time to tassel emergency, time to silk emergency, number of rows/ear, number of kernels/row, grain yield/plant and shelling percentage and higher than unity for plant height and 100-Kernel weigh.  Significant positive general combining ability (GCA) effects were found for most studied traits. The best combiners were P2 (P79) and P4 (Inb.1021) for earliness traits; P5 (Inb.1004) and P6 (Oh.43) for plant height; P5 (Inb.1004) for number of rows/ear; P1 (R39) for number of grains/row; P2 (P97), P3 (B73) and P4 (Inb.1021) for 100-grain weight; P1 (R39) for grain yield/plant; P1 (R39) and P2 (P97) for shelling percentage.  Significant positive specific combining ability (SCA) effects were found for most studied traits. The best cross combinations P3×P4 for number of rows/ear; P1×P5 for number of grains/row; P1×P3, P1×P6, P2×P3, P2×P5, P3×P5 and P4×P6 for 100-Grain weight; P1×P2, P1×P5, P2×P5, P3×P6 and P4×P5 for grain yield/plant; P1×P5, P3×P6 and P4×P5 for shelling percentage.  Results showed significant or highly significant heterosis over mid-parents and better parents for all studied traits. The best crosses over mid and better parents were (P1×P5) for number of rows/ear; (P1×P6) for number of grains/row; (P2×P5) for100-grain weight;(P1×P6)for grain yield and (P1×P4) for shelling percentage.  The study recommends using inbred line P3 (B73) and crosses P1×P2, P1×P3 and P3×P6 in breeding program of maize to improve the yield and its components where they recorded the highest value of the grain yield/plant and gave a better combining ability.

This investigation was carried out at Sakha Agric. Res. Stat. KafrelSheikh, Agric. Res. Centre, Egypt, during 2014 and 2015 growing seasons. A study was undertaken on some genotypes of Egyptian cotton (Gossypium barbadense L.) to estimate the mean performance, heterosis over better parent (heterobeltiosis), combining ability and type of gene action for some earliness, yield and its components traits in some Egyptian cotton genotypes by using line x tester mating design between seven cotton genotypes i.e.,

In 2012, six maize inbred lines were crossed in all possible combinations without reciprocals by using a half diallel cross mating design to obtain 15 single crosses. 15 F 1 single crosses were evaluated through 2013 season under 2 irrigation treatments, every 12 day (Normal irrigation) and every 18 days (stress), to assess the role of general and specific combining ability of inbreds in hybrid behavior under recommended irrigation and water stress conditions. Results showed that mean squares due to crosses, general (GCA) and specific (SCA) combining abilities were significant or highly significant for all studied traits under both nonstressed and water stressed conditions, except of SCA for plant height under both conditions, which was insignificant. This result indicated that both additive and non-additive gene effects are very important in the inheritance of these traits. The ratio of GCA/SCA were less than unity for anthesis date under both conditions, silking date under normal irrigation, ear leaf area at stress condition, ear length under both conditions, and ears yield per plant at stress condition, indicating that the non-additive genetic effects were more important and played the major role in the inheritance of these traits under these conditions. On the other hand, GCA/SCA ratios were more than unity for silking date under stress condition, ear leaf area at normal irrigation, plant height under both normal and stress conditions, and ears yield per plant at normal condition, indicating that the additive genetic effects were more important and played the major role in the inheritance of these traits under these conditions. The best general combiners were: P 2 (Rg5) and P6(B 73) under both conditions, and P4 (R39) under normal for earliness;P1(Inb. 209),P5(Sids7) under normal, and P2 (Rg5) under both conditions for ear leaf area; P5(sids7) under normal, and P6(B73) under both conditions for plant height(shortness);P1(Inb.209) and P3(sids34) under both conditions for ear length; and P1 (Inb.209) under normal, and P2 (Rg 5) under both conditions and P4 (R39) under stress for ears yield per plant. The best cross combinations were: eight crosses (No. 3, 4, 5, 6 , 9, 10, 12 and 13) under normal, and five crosses (No. 2, 3, 6, 9 and 13) under stress for earliness; two crosses No. 2 and No. 12 under normal, and three crosses No. 6, 13 and 15 under stress for ear leaf area; crosses No. 5 and 6 under normal and cross No.5 under water stress for plant height (shortness);four crosses i.e. No.4, 8,10and 12 under normal, and four crosses No. 2, 12,13 and 15 under stress for ear length; and three crosses i.e. No. 1, 12 and 13 under normal, and six crosses No. 2, 4, 6, 12, 13 and 15 under stress for ears yield per plant.

Combining ability estimation is an important genetic attribute for maize breeders in anticipating improvement in productivity via hybridization and selection. This research was carried out to investigate the genetic structure of the 27 F1 maize hybrids established from nine lines derived from Maize Research Department and three testers, to determine general combining ability (GCA), determine crosses showing specific combining ability (SCA) and superiority percentages for crosses. Nine lines, three testers, 27 F1 hybrids and two check commercial hybrids (SC162 and SC168) were studied in randomized complete block Design (RCBD) with three replications during 2016. The results of mean squares showed that significant and highly significant for most studied traits (days to 50% tasseling, days to 50% silking, plant and ear height, ear position, ear length, no. of kernels per row, 100-kernel weight and Grain yield). Estimates of variance due to GCA and SCA and their ratio revealed predominantly non-additive gene effects for all studied traits. Lines with the best GCA effects were: P2 (line 11) and P6 (line 21) for grain yield, for testers Gm174 and Gm1021 had significant GCA effects for grain yield. The hybrids P5×Gm1021, P6×Gm1021, P7×Gm1021, P8×Gm1002, P9×Gm1002 had significant and negative SCA effects for grain yield. Crosses P1×Gm174, P2×Gm1002, P5×Gm1021, P6×Gm174, P6×Gm1021, P7×Gm1021, P8×Gm1002, P9×Gm1021 were the best combinations manifested and significant superiority percentages over than check varieties (SC162 and SC168) for most studied traits. Therefore, these hybrids may be preferred for hybrid crop development. Abbreviations: GCA general combining ability; SCA specific combining ability

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Two series field experiments were done for the period of 2014/2015 and 2015/2016 seasons at Abo-Saied Village, Kafr El-Sheikh Center, Kafr El-Sheikh Governorate to study the effect of plant population and distribution and nitrogen levels on yield and quality of sugar beet, "CV. Zwan Poly". The studied plant distributions were 25, 30 and 35 cm on both sides of terrace (Mastaba) 80 cm width and 20, 24 and 28 cm on both sides of terrace (Mastaba) 100 cm width, which resulted in three plant populations of 30000, 35000 and 42000 plants/fad. The used design was split-plot with 4 replicates. Results showed that plant population and distribution had significant effects on all studied traits. Cultivating beet seeds at 35 cm distance between hills on both sides of mastaba 80 cm width (30000 plants/fad) resulting significant increases in number of leaves/plant, foliage fresh weight/plant, plant weight, root weight as well as sucrose percentage, total soluble solids(TSS) and purity percentages. Increasing N-levels from 69 to 92 and 115 kg N/fad significantly increased root weight, root diameter, root length, number of leaves, foliage fresh weight/ plant and plant weight in both years, while it significantly decreased sucrose, TSS and purity percentages in both years. Generally, it could be accomplished that cultivating sugar beet on both sides of mastaba 80 cm width and 25 cm between hills and fertilizing plants with 115.0 kg N/fad could be recommended for maximizing root yield under the ecological circumstances of this research.