To evaluate the effect of environment on the GENERAL and specific COMBINING ABILITY of Virginia tobacco genotypes, five varieties were intercrossed in combination in 2007 in a Half – diallel design. In 2008, the ten F1 population and the five parental lines were sown in two different conditions (drought stress and non-stress) using a complete randomized block design with three replications and two locations (Tirtash and Rasht Tobacco Research Center). The studied traits were: leaf length, leaf width, leaf numbers per plant, leaf area index, plant height and dry leaf yield. Dialle analysis in all environments revealed interactions of GCA×E for most traits, emphasizing the importance of calculation of effects for each environment separately. SCA×E was highly significant for all traits except for the chlorophyll content and leaf area index, indicating that the specific hybrids weren’t stable across the environments. The significant interactions indicated that the magnitude of differences among GCA and SCA effects of genotypes changed with environment. In GENERAL, the GCA/SCA ratio over all environments was significant for all quantitative traits except for leaf length, indicating the predominant role of additive genetic effects in the inheritance of most traits. The cultivars NC89 and k394 were the best GENERAL combiners, while NC89×k394, VE1×Coker254, Coker347×Coker254 were the best specific combinations for dry leaf yield over all investigated environment.

The leaf number per seedling length of longest stem cotyledon length and width, unifoliate internode length and leaf blade length and width were measured on over 2000 individual 30-days old seedlings. The seedlings were transplanted to the field and individual plants fresh and dry weight number of shoots per plant and plant height were measured on 900 plants in each of four harvests. Days until 50% flowering percentage of ground cover fresh and dry weight of leaves/plant ratio and size of trifoliate leaves were also measured in experimental plots. The path analysis for yield indicated that most effective traits on fresh and dry yield are plant height and number of shoots respectively. Based on multivariate analysis of variance of 30 half-sib families for all traits measured on seedling and mature plants significant differences were obtained showing genetic variation between families under study. Additive variance for most traits was significant. HeritABILITY based on family mean was more than individual plant base. GENERAL COMBINING ABILITY for yield and relative traits were estimated. This information will be used for constructing synthetic varieties from families having good GENERAL COMBINING ABILITY.

At the recent years, many sunflower restorer lines (Rf-lines) have been derived from exotic sunflower hybrids in Seed and Plant Improvement Institute at Karaj. Twenty four of these new Rf-lines (Resistant to Plasmopara halstedii), were crossed with three testers at the Oilseed Crops Research Department. Sixty hybrid combinations were evaluated in replicated field trials to estimate the GENERAL COMBINING ABILITY (GCA), and the gene effects. Analysis of the GENERAL COMBINING ABILITY for the grain yield and seed oil content showed that R-43, R-72, R-82, R-217, R-231, R-256, R-103, R-87, R-55 and R-45 for grain yield and R-43, R-256, R-46, R-87 and R-45 for oil seed content had high GCA values. Evaluation of gene effects indicated the involvement of additive and nonadditive effects for plant height, growth duration, head diameter, 1000 seed weight, grain yield and merely additive effect for seed oil content.

To produce new hybrids and study the COMBINING ABILITY of new sunflower inbred lines, 60 F1 hybrids derived from crossing between 30 inbred lines and 2 testers along with Azargol, SHF81-85, SHF81-90 and Cms1052/1*14 as checks were evaluated using simple lattice design with two replications in Agricultural Research Station of Islamabad-e-Gharb in 2011. Analysis of variance showed that genotypes were significantly different for all recorded traits except days to end of flowering and seed oil content. Hybrids B86-353.1AF81-196, B86-284.1AF81-196 and B86-345.1AF81-196 had the highest seed yield (5583, 5331 and 5235 kgha-1, respectively). COMBINING ABILITY analysis using design II of Comstock and Robinson showed that GENERAL COMBINING ABILITY of inbred lines and testers for seed yield was significant at 1% level. Inbred lines B86-353, B86-284 and B86-345 had the highest GENERAL COMBINING ABILITY for seed yield, whereas inbred lines B86-373.2 and B86-382.2 had the highest negative COMBINING ABILITY for days to maturity. Specific COMBINING ABILITY effect was significant for some agronomic traits such as seed yield, head diameter, plant height and days to maturity. The highest specific COMBINING ABILITY for seed yield belonged to hybrids B86-300.2AF81-112 and B86-346.2AF81-112. Hybrid B86-287.1AF81-196 had the highest negative specific COMBINING ABILITY for days to maturity.

To study COMBINING ABILITY and genetic parameters of seed yield trait in rapeseed, eight lines of rapeseed were evaluated by a design of half diallel cross. Seeds of F1 generation and their parents were grown in a 6 × 6 simple lattice design with two replications. According to the analysis of variance, GENERAL COMBINING ABILITY (GCA), specific COMBINING ABILITY (SCA) and mean squares of genotypes were significant for seed yield at 0.05 and 0.01 probABILITY level, respectively. We used GGE biplot approach for graphical diallel cross analysis. The biplot displays the most important entry by tester patterns of the data and allows the information to be extracted visually. The biplot analysis indicated that the first two principal components explained 74.3% (47.7 and 26.6% by PC1 and PC2, respectively) of the variation for seed yield. GGE biplot graphical procedure results indicated that one parent, Opera, had the highest positive GCA and parents of Fornax had the highest negative GCA. The largest SCA obtained from ORIENT and the smallest SCA came from TALAYE. Also, the SCA mostly came from OPERA and TALAYE, ORIENT and TALAYE. Overall, the results of this study suggest that, within individual hybrid crosses, sufficient heterosis for yield exists to justify hybrid development in rapeseed.

In order to produce new hybrids and evaluate the GENERAL and specific COMBINING ABILITY of sunflower inbred lines and restorers, four inbred lines and six restorers were selected in 2004. Twenty-four F1 hybrids were derived in 2004 and evaluated on a RCBD design with three replications in 2005. The results of variance analysis showed that treatments were significantly different for all traits except grain yield. RHa107F81-127/2×Aha107F81-240, Azargol and RHa107F81-127/2×AHa107F81-30 had the highest grain yield with 4471, 4274 and 4131 kgha-1, respectively.  Variance analysis of COMBINING ABILITY by design II of Comstock and Robinson showed that GENERAL COMBINING ABILITY of restorers and inbred lines for grain yield was not significant. Rha107F81-127/2 restorer and AhaF81-120 inbred had the greatest GENERAL COMBINING ABILITY for grain yield.  The results GENERALly showed that male parents or restorers play important role to produce hybrid cultivars and Rha107F81-127/2 has a good potential to be applied in breeding programs.

GENERAL COMBINING ABILITY of sugar beet parents were determined for different quantity and quality characteristics. Forty six sugar beet hybrids obtained from crosses of 23 diploid pollinators with two male sterile parents as tester together with three checks were evaluated for 10 important agronomic and technological characters at Kamalshar Research Station in Karaj in 2004.Experiment was carried out as a 7*7 lattice design with four replications. There were significant differences between treatments for root yield, sugar content, nitrogen, sodium, potassium, white sugar yield, extractable sugar, sugar yield, purity and molassed sugar at 1% probABILITY level. The check varieties were excluded before the analysis of data for COMBINING abilities. GENERAL COMBINING ABILITY of lines was significantly different for sugar content and extractable sugar at 1% and for root yield, sugar yield, white sugar yield, sodium, purity, and molassed sugar at 10% probABILITY level and for potassium at 5% probABILITY level. As the GENERAL COMBINING ABILITY was significant for the above traits it could be concluded that they are controlled by additive gene effects. In addition, specific COMBINING ABILITY of lines was significantly different for sugar content, extractable sugar and potassium at 1% and for nitrogen at 5% probABILITY levels. There for, non-additive effects of genes are involved in the control of these traits. 

The present research was carried out for evaluation of GENERAL COMBINING ABILITY of P. atlantica. Parental trees were selected, isolated, pollinated and finally the fruits were harvested, in 2002 and 2004. Some characteristics were measured in seed technology laboratory and remaining seeds were sown and some characters were measured in field. The highest cross abilities for fruitfulness (%) was obtained in crossed female 9 with male 3 and 11, in 2002. The most seed producer belonged to cross 9 female with 9 or 11 as males. The highest germination percentage was found in females 12, 13 and 8 when crossed with all of the males, in 2002. It is worth knowing that female 9 showed a good performance in the most measured characteristics. The highest seed weights were shown to be in crossing of males 8, 10 and 1, in 2004. Meanwhile, the best combiners among maternal trees were 22, 18 and 12. The most superior parents for seed weight production in 2004 were shown to belong to males 4, 8 and 1 and the best maternal combiner trees were 22, 21 According to the results, males number 10 and 11 and females 9 and 13 in 2002, and females 17, 18, 21 and 22 and male 1 and 8 in 2004, have shown to be the superior P. atlantica trees. Thus, in order to improve P. atlantica for achievement of successful seed and seedling production, a pilot plan could be beneficial.

Objectives of the study were to assess GENERAL COMBINING ABILITY on fifty genotypes of tall fescue. During 2006, the genotypes were sown in the nursery polycross. Polycross seeds were sown based ob a randomized complete block design with 3 replications to evaluate GENERAL COMBINING ABILITY of several traits in tall fescue during 2007. Analysis of variance showed significant differences among the genotypes for most of the studied traits. The highest coefficients of variation were obtained for forage dry yield, forage fresh yield, number of stems and rust resistance. Least coefficients of variation were obtained for crown diameter per plant, plant height and peduncle length. Broad-sense heritABILITY was very high for forage dry yield, forage fresh yield, number of stems, crown diameter per plant and plant height. Genetic advance was optimistic for dry yield, forage fresh yield and number of stems. Cluster analysis classified the genotypes into three groupes. Using principal components analysis, the first three components determined 78/80% of the total variance. GCA for trait forage dry yield, forage fresh yield, number of stems, crown diameter per plant were the most important traits in the first component. The highest values were observed for GCA on 9 genotypes for forage dry yield and forage fresh yield, 10 genotypes for crown diameter per plant, 5 genotypes for plant height and 5 genotypes for peduncle length. Thus, selecting genotypes for the characters must be effective in achieving suitable parent for producing synthetic variety.

During early stages of breeding programs for large populations of forage plants, GENERAL COMBINING ABILITY (GCA) can be used to select superior families for development of a synthetic variety. Tall fescue is one of fescue species that are economically important and widely used as a forage grass. Tall fescue is self-incompatible and wind cross pollinated. This study was conducted to evaluate GENERAL COMBINING ABILITY of 25 polycross families of the species during 2012 and 2013 at a research station in Isfahan, in center part of Iran. Number of days to pollination, plant height, number of fertile tiller, length, and width of flag leaf, spike length, seed and forage yield of the families were evaluated. For number of days to pollination, genotype 13 and genotype 23 had the most and the least GCA (6.24 and -7.76), respectively. For fresh forage yield and dry forage yield, genotypes numbered 15, 18 and 19, 20, 23 and 24 had the most GCA. The six mentioned genotypes also had the most values for seed yield. It seems that crosses between the genotypes may produce synthetic varieties with high yield capacity. Cluster analysis grouped the families in four clusters. Analysis of variance showed that the third group had the highest mean for forage yield. Variation in GCA values was observed in most of the studied traits. Simultaneous studies of cluster analysis and GCA of the genotypes can help to find the best parental genotypes to produce synthetic varieties in future breeding programs.