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 t...esters, 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
Two field experiments were carried out during the 2014 and 2015 seasons to evaluate certain genotypes of Egyptian cotton under well irrigated and water stress conditions. The cross combination Giza 69 x Australy recorded the best values for better parent heterosis for all physiological measurements and earliness index under well irrigated a...nd deficit conditions. Of the female parents, Giza 86 was found to be a good general combiner for most yield characters under both normal and stress conditions, followed by Giza 94. Data illustrated that Giza 45 was the best general combiner for most fiber quality traits under both conditions. The cross combinations Giza 86 x Dandra and Giza 69 x Pima S6 showed significant positive SCA values for seed cotton and lint yield/plant under well irrigated and water deficit conditions. However, the combinations Giza 77 x PimaS6 and Giza 94 x 10229 recorded significant positive SCA effects for seed cotton yield/plant under stress. Whilst, the cross Giza 68 x 10229 recorded significant desirable SCA effects for most fiber quality properties. In this context, the estimates significant positive general and specific combining ability effects indicated that the epistasis and/or dominance effects for F1 hybrid in cotton could be important to a certain extent.
Grain number per spike was studed in 6 winter wheat varieties and all their 30 direct and reciprocal F1 hybrids. Parents
included 4 released Romanian variety, the old american Atlas 66 and a dwarf breeding line, Oradea 79. This line has a low number of
grains/spike, but is important in breeding program for here reduced height. General and
genetic effects were estimated using Griffing’s method 1, model 1, as modified by Cabulea (1983).
For this diallel crosses, gene interactions and the interaction between cytoplasm and nuclear genes were highly significant and
the ratio of additive and non-additive effects was close to one.
The variety Fundulea 29 showed the highest general combining ability and it is recommended as a good parent for increasing
grain number/spike. Mid-parent heterosis was significant in 9 out of the 30 cases, mostly in hybrids involving the breeding line Oradea 79.
In 3 cases the number of grains/spike of F1 hybrids was significantly lower than the average of the parents. The breeding line Oradea 79 had
a significant negative general combining ability, but showed significant positive specific combining ability in most crosses, as well as a
significant positive effect of its cytoplasm. These results are considered to indicate that there are chances of improving the grain
number/spike in some crosses with Oradea 79.