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.

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 achieve favorable outcomes in breeding programs, selection of parents based on General COMBINING ABILITY (GCA) and Specific COMBINING ABILITY (SCA) is so important. In order to study the genetic parameters, general and specific COMBINING abilities and the type of disease resistance genes action against take-all disease in bread wheat, 6 wheat genotypes (729, 1622, 2109, 1528, 1546 and 1526) were crossed in one-way diallel cross. Seeds of F1 generations (F1s) and parents were planted in the research greenhouse of Vali-e-Asr University of Rafsanjan, Iran and take-all disease tolerance, stem and root dry weights, tiller number and elements such as manganese (Mn), zink (Zn), potassium (K) and iron (Fe) concentrations in plant tissue were measured. The results of Griffing analysis showed that general and specific COMBINING abilities were significant for all traits except tiller number and K element. In terms of Take-all disease resistance, the best general combiners were 1622 and 729 genotypes, respectively. The best resistant hybrids were 2109×1546, 546×1528 and 1622×1526 that had the highest specific COMBINING ABILITY. Evaluation of genetic parameters by Hayman method for disease index and disease score confirmed the results of Griffing analysis and showed that the dominance and over dominance of gene actions had the greatest importance in genetic control of the resistance to take-all disease (T-41 isolation). Finally, due to low narrow sense heritABILITY and low genetic ratio in resistance to take-all disease, it can be concluded that selection for resistance to take-all disease does not respond well in early generations, so selection after purity, that done by bulk, single-seed descent and double haploid methods can be effective in wheat breeding.

IntroductionLow diversity and poor genetic basis of germplasm in temperate regions is a significant challenge in maize breeding. Maize germplasms from tropical and subtropical regions often contain a broader genetic base and show larger diversity than germplasms from temperate regions. Therefore, it seems that foreign germplasms, especially germplasms from tropical and subtropical regions, can be used as a potential solution to strengthen the genetic base of germplasm in temperate regions. However, the efficiency of screening methods to identify superior and suitable sources of foreign germplasm remains a major challenge. The objective of this study was to determine the optimum number of testers and select suitable testers for screening maize lines derived from tropical and subtropical CIMMYT germplasm.Materials and methodsIn this experiment, three testers of temperate regions (MO17, B73, K1264/5-1) were crossed with 25 lines originated from the CIMMYT maize germplasm based on line × tester mating system. A total of 75 crosses along with the control hybrid (SC704) were evaluated in alpha-lattice experimental design in two replications each with four incomplete blocks in two regions (Moghan and Jiroft). Analysis of variance was done based on line × tester method, as well as separation of the effect of crosses into its components using the method suggested by Kemptorn (1957). GGE-biplot graphical analysis based on the methodology proposed by Fan et al. (2010) was also used to estimate the effects of general COMBINING ABILITY (GCA) and specific COMBINING ABILITY (SCA).Research findingsThe results showed that out of the 75 crosses, 32 crosses had higher and significant grain yield compared to the control hybrid SC704. The superiority of the superior cross compared to the control hybrid ranged from 1.46 to 3.77 tons per hectare. These findings highlighted the potential of utilizing tropical and subtropical CIMMYT germplasm to enhance maize yield in temperate regions of Iran. Based on the results, the lines No. 22, 9, 19, 12, 20, 5, 17, 21, 24, 14, 15, 23, and 11 had the highest positive GCA for grain yield, respectively. In general, in terms of grain yield, GCA, and SCA, it is possible to directly use lines No. 4, 5, 9, 11, 12, 19, 22, and 24 extracted from tropical and subtropical CIMMYT germplasm to improve grain yield in temperate regions. Evaluating the efficiency of the temperate maize testers also showed that two testers B73 and MO17 were highly efficient in selecting superior line derived from tropical and subtropical CIMMYT germplasm.ConclusionThe results of the current study showed that it is possible to use maize germplasms from tropical and subtropical regions of CYMMIT to improve grain yield in temperate regions. Also, one temperate maize tester has the ABILITY to distinguish superior sources (not all of them), although the use of two testers greatly reduces the risk of not choosing (deleion) a superior source.

Quantitative valuations of observed heterosis for 11 traits of 15 F1 hybrids generated by half diallel crosses of six diverse rice cultivars (Domsefid, Hashemi and Binam, three Iranian local cultivars; Dorfak, Kadous and IR30, three improved cultivars), were made in this study. Fifteen F1 hybrids and their parents were evaluated in a randomized complete block design with three replications at the Research Farm of the University of Guilan at Rasht, (Iran) in 2006. The studied traits were growth period, reproductive period, flag leaf area, plant height, panicle length, number of panicles per plant, number of grains per panicle, 1000-grain weight, grain yield, brown grain length and brown grain width. The significance of specific COMBINING ABILITY (SCA) and general COMBINING ABILITY (GCA) for all studied traits revealed that both additive and non-additive gene effects contributed to the inheritance of the traits. Assessment of standard heterosis based on check variety Dorfak showed that there was significant heterosis for all the traits studied in the 15 hybrids. For grain yield, the Dorfak×Domsefid cross had the highest heterosis.This hybrid had good heterosis values for many traits such as growth period, reproductive period and 1000-grain weight and was recommended as the most promising combination for developing high yielding hybrid rice varieties.

Five CMS lines and four restorer lines (tester) were crossed in a line × tester scheme in order to analyze general and specific COMBINING abilities and gene effects in sunflower for some agronomic traits. Hybrids were evaluated in a randomized complete block design, with three replications under optimum and limited water conditions in the Agriculture Research Station, Khoy, during 2015 and 2016 growing seasons. Plant height, head diameter, seeds per head, days to beginning of flowering, days to maturity, proline percent, protein percent, and Chlorophyll b were found to be controlled mainly by dominance effects. CMS lines AGK30 and testers RGHK25 and RGHK50 turned out to be the best general combiners for seed and oil yield. The highest positive and significant GCA for plant height, head diameter, and the number of seeds per head were achieved for RGHK25. The hybrid combination of AGK44 × RGHK56 showed high specific COMBINING ABILITY for seed and oil yield. In the study of general COMBINING ABILITY, the AGK110 line has a positive and consistent general COMBINING ABILITY, and AGK2 has a negative and significant general COMBINING ABILITY with catalase. In the test of the testers, the tester (RGHK50) had the highest GCA positive and meaningful drug tester (RGHK56), which had a significant negative and significant COMBINING ABILITY with catalase. In the study of hybrid hybrid COMBINING ABILITY (RGHK46 × AGK260), the highest positive and significant positive and significant hybrid confinement (RGHK46 × AGK44) had the highest SCA negative and significant levels. In the RGHK46 × AGK260 hybrid combinABILITY study, the highest positive and significant positive and significant hybrid confinement (RGHK46 × AGK44) had the highest SCA negative and significant effect on catalase identity. The AGK44 line has the ABILITY to combine publicly and positively with AGK110 capABILITY. The general COMBINING ABILITY was negative and significant with SOD. In the test of the testers, the RGHK 56 tester had the highest GCA positive and significant mean of the RGHK25 tester, which had a negative and significant general COMBINING ABILITY with superoxide dismutase. In the study of hybrid hybrid COMBINING ABILITY (RGHK50 × AGK260), the highest positive and significant positive and significant positive COMBINING ABILITY (RGHK50 × AGK44) had the highest SCA negative and significant values for SOD. In explaining the traits, plant height, Number of seeds per head and percentage of proline under stress conditions played a more significant role. Plant height and number of seeds per head were controlled by both growth and dominance effects. also In the study of general COMBINING ABILITY, the highest GCA positive and significant values were related to the AGK30 line and the most general negative and significant general COMBINING ABILITY was AGK2 line (Table 4-14). In the test of the testers, the tester (RGHK 46) had the highest GCA positive The drug tester (RGHK25) had the most significant negative and significant general COMBINING ABILITY with proline). In the study of hybrid COMBINING ABILITY (RGHK46 × AGK2), the highest positive and significant positive and significant hybrid confinement (RGHK25 × AGK260) had the highest SCA negative and significant values.

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.