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Nigella sativa</em> L. is an important medicinal plant widely used in the food and pharmaceutical industries. Considering the increasing demand for medicinal plants worldwide and the need to produce cultivated and breeding varieties, it is necessary to study the genetic resources. The gain from selection for a trait depends on the relative importance of genetic factors in the occurrence of phenotypic differences among genotypes; in other words, the success of breeding programs depends on the genetic variation and heritability of traits. Therefore, this study investigated the genetic variation and inheritance of seed yield and yield component traits in different black cumin genotypes and identified desirable genotypes for use in breeding programs.

This study investigated the genetic variation in 20 different black cumin genotypes (Iranian and foreign) regarding different agronomic traits as a randomized complete block design with three replications at the research farm of Shahrekord University. The genotypes were planted in the middle of March. Each genotype in every repetition was cultivated in four rows, each 1.5 meters long. The distance between the rows of cultivation was 30 cm, with seeds planted 15 cm apart within the row at a depth of 1-2 cm. The traits studied included seed yield, number of capsules per plant, number of seeds per capsule, thousand seed weight, capsule diameter, number of branches per plant, and plant height. Based on the expectation of mean square components, environmental, genetic, and phenotypic variance were calculated, and then the genotypic and phenotypic coefficient of variation and broad-sense heritability were estimated. Statistical analyses, including analysis of variance and comparison of the mean traits between genotypes, were performed using the least significant difference (LSD) test using SAS 9.0 software. Pearson correlation between traits and cluster analysis based on Ward's method according to squared Euclidean distance using R 3.6.1 software. Also, to ensure the correctness of grouping, multivariate tests and analysis of variance tests were performed based on a completely random, unbalanced design.

The analysis of variance showed a significant difference between the studied genotypes for all the agronomic traits (p<0.01</em>). The plant height in the studied genotypes varied from 22 cm (Nige7) to 58.4 cm (Nige1). The highest number of capsules per plant was observed in the Nige 53 genotype, with 20.45 capsules, and the lowest number of capsules per plant was observed in the Nige63 genotype, with 5.3 capsules. The number of branches per plant ranged from 3.9-11.5 per plant. The yield ranged from 263.56 kg/ha (Nige3) to 1409.39 kg/ha (Nige78 genotype). The phenotypic coefficient of variation varied from 48.58% (seed performance) to 5.20 (capsule diameter), and the genotypic coefficient of variation varied from 48.29% (seed performance) to 4.7 (capsule diameter). The highest genetic coefficient of variation (48.29%) belonged to the grain yield trait. The estimated heritability for the assessed traits ranged from 73.81% for number of branches per plant to 98.8% for seed yield. Heritability was 91.91% for the number of capsules per plant trait. According to the correlation coefficient results, seed yield per plant showed a positive and significant correlation with the number of capsules per plant (r=0.87**) and branches per plant (r=0.54*). In the cluster analysis, the studied genotypes were divided into four different groups, and the results of the multivariate analyses indicated appropriate grouping and significant differences in the amount of grain yield and yield components among the groups resulting from the cluster analysis.

The high genetic variation among the studied genotypes indicates the high efficiency of this germplasm for improving grain yield and various traits and the high efficiency of selection in black cumin. Genotypes Nige53, Nige78, and Nige60 had high grain yields compared to other genotypes, which can be used to improve and increase grain yield in black cumin.

To study the general and specific combining ability and heterosis of six tomato lines, a 6×6 diallel design was used. The parents of the crosses were lines 486 (P1), 208 (P2), 151.6 (P3), Kim (P4), 1010 (P5), and 542 (P6) with different characteristics for yield and other studied traits. All lines were obtained from the Vegetables and Irrigated Pulse Crops Research Department, Seed and Plant Improvement Institute, Karaj, Iran. The parents together with 15 F1 hybrids resulting from their half-diallel crosses (21 genotypes) were planted in a randomized complete block design with three replications in the research farm of Qazvin Agricultural Research Center, in 2019, and fruit yield, number of fruits per plant, fruit weight and total soluble solids (TSS) were measured. The results of the analysis of variance based on second Griffing’s method with the assumption of fixed parents showed that the difference among all genotypes and the difference in general combining ability (GCA) of parents and the specific combining ability (SCA) of hybrids were significant for all studied traits, indicating the role of both additive and non-additive gene effects in the inheritance of traits. Baker's ratio as well as Hung and Holland's ratio for all studied traits were obtained from 0.5 to 1.0, which indicated the role of both additive and non-additive gene effects with the higher contribution of additive effects in controlling all traits. A comparison of parents showed that Kim for fruit yield and number of fruits per plant, line 1010 for fruit weight, and line 468 for TSS had the highest positive and significant GCA. Among the hybrids, hybrid 1010×151.6 for fruit yield and fruit weight, Kim×542 for number of fruits per plant, and Kim×151.6 for TSS had the highest positive and significant SCA. In total, the results of this experiment showed that hybrids 151.6×208 and 151.6×1010 for fruit weight, hybrid 542×1010 for the number of fruits per plant and hybrid 151.6×208 for TSS had the highest positive and significantly better parent heterosis (heterobeltiosis), and were the most valuable hybrids in this experiment, but for fruit weight, only hybrid 468×151.6 had positive and significant mid-parent (standard) heterosis.

 Cantaloupes, are a group of Cucumis melo cultivars, that have round, fragrant fruits with netted skin. Our country, is one of the top five producers of cantaloupe, and melon in the world. Its original origin, is still debated, but one of the important centers of its diversity, is Iran. Although, native cultivars, such as, Saveh cantaloupe, Samsoori, Rish Baba, and various types of Tiles, are often of good quality, and taste, but they are sensitive to a variety of fungal and viral diseases and as a result, their yield is low. On the other hand, every year new cultivars and hybrids, are introduced by seed companies, which are welcomed by farmers, due to, their better agronomic characteristics, and resistance to a wider range of diseases. Continuation of this process, in addition to severe genetic erosion of native cultivars, and populations, and even the complete elimination of some of them, will have consequences such as, dependence of production on foreign companies, annual departure of currency from the country, and non-exploitation of the country's genetic resources. Therefore, it seemed that by creating a diverse population resulting from the crossing of superior native cultivars with cultivars of commercially resistant hybrid to diseases, and then, successive selections, new cultivars, with desirable traits of both parents, could be achieved. Thus, in this study, heritability, minimum and maximum mean values of parents, and F1 and F2 generations, aggressive segregation, and relative frequency of qualitative traits, in F2 generation, and selection of the best genotypes, in two dispersing NGF2 populations, were investigated.

 Parental cross, was performed in the spring of 2017, between Samsoori cantaloupe cultivar (round, striped fruit, cream skin color, completely reticulate, green flesh, very early ripening fruit, poor transportability and durability, free pollinator and high homogeneity) as the selected native paternal parent, and commercial cultivar from Gallia group, that called Cory and as maternal parent (round fruit, completely reticulate, no striped skin, yellow to cream skin color, high transportability and durability, green and very sweet flesh, high resistance to various plant diseases and viral diseases) and produced by Seminis Company. The first-generation seeds, obtained from parental crosses, were planted in the greenhouse in the fall of 2017, and were self-sown. In the spring of 1397, 1000 seeds of F2 generation, along with parent seeds, and their first generation, were planted in a seedling tray, in the greenhouses of the Faculty of Agricultural Technology (Aborihan) of Tehran University, and transplanted to the ground, in the rental research production farm, located, in Filistan village-Golzar sector-Pakdasht. Controlled pollination, (isolation of male flowers, and manual inoculation) was performed, for all second-generation plants. Selection for subsequent generations, was done by pedigree method, all plants in F2 generation, were evaluated, and selected. Morphological traits, such as, plant form and phenological traits, such as, day to fruit harvest, were evaluated, and recorded. Plant health, was assessed against common and important fungal, viral and mites, under normal field conditions by scoring the severity of infections in four categories. Fruit quality traits were measured based on nominal, sequential and interval scales and quantitative fruit traits were also measured. Tables of minimum and maximum values, variances, general heritability, transgressive segregation, etc for quantitative traits, also relative frequency percentages and observed genetic ratios for quantitative traits, were calculated.

 The results showed that all quantitative traits in the F2 population had a general heritability above 90%. The mean of all quantitative traits except soluble solids and fruit flesh thickness in F1 population was lower than the parental average. In F2 population, for all quantitative traits, positive transgressive segregation was observed, compared to, the superior parent, and negative transgressive segregation was observed, compared to, the less valuable parent. In the F2 population, nearly 80% of the genotypes, were completely reticulate, and 20% had less or no netting, on the fruit skin. These results were almost consistent with genetic ratios of 3.1. Also, 35% of F2 population genotypes, were striped and more than 80% of them had yellowish skin color and green flesh color. Due to, the fact that, selection based on traits with high heritability, will be more reliable, and successful in early generations, so, it is better, to select the best genotypes, in this population, based on fruit weight, soluble solids, and early maturity, respectively.

In the F2 population, positive transgressive segregation was evident for all quantitative traits, favoring the superior parent, while negative segregation was observed for the less valuable parent. Traits exhibiting high heritability showcased a pronounced influence of genetic variance over environmental variance. Consequently, selecting cultivars based on these traits in early generations is expected to yield more reliable and successful outcomes. Therefore, it is better, to selection, the best genotypes in the early generations, in the F2 population, based on fruit weight, (with high genetic efficiency), soluble solids, day to fruit ripening, and with the pedigree management, of the populations, it is finally, possible to achieve lines, that have the desirable traits, of both parental cultivars. The resulting lines, can be used to produce, new hybrids, or provided, to the farmer, as a single cultivar.

Creating new efficient technologies such as doubled haploids is a fast solution for producing inbred lines. In this study, using the microspore embryogenesis method, doubled haploid (inbred) pepper lines were produced. The Topcross test was performed using 32 doubled-haploid lines produced and the topcross parent of California Wonder to examine the general combining ability of the lines. Hybrids derived from crosses line × tester in 2018- 2019 were planted. In order to evaluate the general combining ability of the lines, days to germination, days to flowering, days to fruit set, fresh fruit weight, dry fruit weight, fruit length, fruit width, thickness of fruit diameter, number of seeds, average yield per plant, number of fruits per plant and plant height were measured and analyzed. Comparison of means by Duncan test showed that top-cross progeny of DH55, DH64, DH57, DH53, DH217, DH202, and DH90 doubled haploid lines respectively with average of 8.58, 7.22, 7.18, 5.99, 5.93, 5.80 and 5.69 kg per plant had the highest fruit yield, among them the highest amount was related to the Topcross offset from DH55× California Wonder with an average of 8.58 kg per plant. The heritability of the evaluated traits was over 70%, among them the number of days to germination and the average fruit yield per plant were the highest. The above-mentioned lines also had the highest positive and significant general combining ability for the average yield per plant. Therefore, these 7 lines can be used as superior parent lines in future breeding programs.

In order to investigate phenotypic and genotypic correlations between physiological characteristics related to drought tolerance and genetic variation and estimating the genetic parameters of these indices in rain-fed condition, 19 genotypes of bread wheat were cultivated in a randomized complete block design with three replications in the research field of Agricultural Research Campus Natural Resources of Razi University of Kermanshah, Iran during 2014-15. analysis of variance (ANOVA) showed significant differences for the grain yield (YS), the cell membrane stability )CMS), the relative water loss )RWL(, the leaf water loss (LWL), the relative water protective (RWP), the water use efficiency )WUE( and the leaf greenish value )LGV( under rain-fed condition. The polygon view of GT biplot showed that genotype no. 12 (wc-4931) was the best genotype compared to other genotypes due to YS, WUE, ELWR and LGV. A high positive genetic and phenotypic relation was observed between WUE and Ys, FV/FM and LWL and, ELWR and LGV. In other hand, High heritability and genetic gain were observed for YS, CMS and WUE that reflect the additive gene action. Accordingly, due to the high propotion of additive effects in CMS, YS and WUE, it was suggested that the evaluation of genotypes must be done at erarly generarion of inbreeding.

In order to investigate the heterosis and genetic relationships of different tomato lines for some qualitative characteristics, five diverse tomato lines were evaluated in a complete diallel cross design. Analysis of variance showed significant differences (P<0.01) among the genotypes for total soluble solids, total acidity, maturity index, antioxidant capacity, ascorbic acid, total flavonoids, and total phenols. The highest heterobeltiosis was observed for total phenol and total flavonoid. Results of Hayman's analysis showed that contributions of additive and non-additive effects were involved in the control of the studied traits. The genetic analysis by Hayman method showed that the attributes except the total phenol, were under the control of the dominance type of the gene action, and their low inheritance indicated the more involvement of non-additive type of gene action. Therefore, due to low heritability and lack of high selection potential, hybridization methods and heterosis phenomenon could be used in the first generation to improve these traits. In contrast, the high specific heritability of total phenol indicated that this trait is controlled by the additive gene effect. Therefore, due to the high selection potential for total phenol, it is possible to modify the population by selection the best genotypes for this trait. Overall, hybridization methods can be used to improve fruit quality traits in tomatoes.

In order to estimate heritability, heterosis, general and specific combinability for traits of leaves number per plant, number of days to first flowering, plant fresh weight, stem fresh weight and the length of the flowering stalk, seven local populations of Iranian lettuce (‘Siahe Dezful’, ‘Gorgan’, ‘Varamin’, Jahrom and ‘18’, ‘21’, ‘27 Mazandaran’) were crossed using a complete diallel crosses design. (These lines were obtained during several generations of selfing in their province). Overall, 49 genotypes including Parents and all possible hybrids were evaluated in a randomized complete block design with three replications. The first method of Griffing’s, Model I was used to estimate the combinability. Analysis of variance revealed high significant differences among F1 hybrids and their parentes for all the studied traits. Therefore analysis of combinabilities showed that general combining ability (GCA) in all the studied traits were greater than specific combining ability (SCA), indicating the importance of additive genes action in controlling these characters than non- additive effects.  High narrow sense heritability (h2ns) for the traits including the length of the flowering stalk and plant fresh weight (0.89 and 0.74, respectively) indicated low effects of environment on the expression of those traits and increased role of additive gene effects. High heterosis effect over the better parent was found for plant fresh weight (11.9 percent) and leaves number per plant (12.42). Results of this research can help to implement more effective and efficient activities in lettuce.

The experiment was carried out on 560 half sib and full sib hybridsof apple during 2014-2015. This study was conducted on 6 and 7 year-old plants in Seed and Plant Improvement Research Institute, Iran. The program related to composed of 7000 seedlings made by 44 cross combinations (2004-2005) based on morphological marker technique in 2006-2007. The plants were grown in the hybrid orchard obtained through a large screening program to select early and mid-early hybrids. In this study, some important quantitative and qualitative pomological traits were evaluated and genotypes were classified into three groups using cluster analysis based on measured traits. In estimation of correlation between phenological traits, there were no significance relationships between yield per tree and growth vigor, period of flowering, flowering density, ripening time and height of tree, but yield had significance and positive correlation with percent of fruit abscission. Flowering density had no significant effect on some phenological traits. In estimation of heritability of some important traits, the highest and lowest general heritability were from yield and period of flowering (64.10% and 5.75%, respectively). General heritability of early ripening was 41.15 percent.

Five CMS lines and four restorer lines (tester) were crossed in a line × tester designe 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 2014 and 2015 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. At grain yield AGK30 line had the highest positive and significant GCA and AGK2 had the highest negative and significant GCA it trait. At evaluation of tester, RGHK50 tester had the highest positive and significant GCA and RGHK56 had the highest negative and significant GCA it trait. At evaluation of specific combining ability RGHK56×AGK44 hybrid had the highest positive and significant SCA and RGHK25× AGK110 hybrid had the highest negative and significant GCA it trait.

To identify the high yielding lines with optimal characteristics, 40 recombinant inbred lines derived from a cross between ‘Norstar’ (winter wheat) and ‘Zagros’ (spring wheat) cultivars were examined using a randomized complete block design with three replications in 2014 at the Research Station of Faculty of Agriculture, University of Tabriz, Iran. The measured characters consisted of peduncle weight, penultimate weight, spike weight, kernels per spikes, biomass, grain yield, 1000 kernel weight, plant height, peduncle length, penultimate length, spike length, harvest index, flag leaf area and straw yield. Significant differences were observed among lines for all the studied traits, except spike weight, flag leaf area and straw yield. Higher genetic diversity was observed among inbred lines with respect to kernels per spike, number of spikes, biomass and straw yield. Peduncle weight, penultimate weight, kernels per spike, number of spikes and 1000 kernel weight had high heritability. The highest genetic gain was obtained for peduncle weight, penultimate weight and kernels per spike. Based on trait means, lines NO 93, 28, 296 and 31 were identified as superior genotypes. Correlation, stepwise regression and path analysis revealed that kernels per spike and number of spikes were more effective components on grain yield. The analyses were carried out using WARD algorithm and standardized data. Cluster analysis was performed based on all traits and lines were classified into four groups. In factor analysis, four first factors explained about 82 percent of total variations.

In order to evaluate genetic diversity among squash landraces from Northwest Iran by morphological and physiological traits، 18 squash landraces belong to pumpkin، ornamental and confectionary groups were planted in completely randomized block design with three replications in Agricultural Research Center of Urmia in 2013. Morphological characteristics related of fruit، seed، leave and flower and physiological characteristics such as photosynthesis rate، TSS and pH were investigated in the studied genotypes. The highest genetic coefficient of variation was observed for fruit yield and plant length. Most of the studied traits had moderate to high heritability. For characteristics such as fruit weight، fruit length، fruit yield and seed yield، the highest expected genetic advance was observed whereas in the cases of primary branching، leaf length، ratio of leaf length to width، flagpole diameter and length and anther length the lowest expected genetic advance was seen. The seven principal components explained approximately 86. 95% of total variance. In the first component، the contribution and importance of traits such as fruit weight، fruit width، internodes، primary branching، fruit yield، seed and 100 seeds weights، TSS، pH، fruit and peduncle lengths، male and female sepals lengths، skin thickness، seed to fruit weight ratio and net photosynthesis rate was high. Based of cluster analysis، the highest genetic distance in the confectionary group was observed between Kenar Burazh and Saatlou landraces، and in the pumpkin group it was observed between Khoy and Zayeh Kandi landraces.

Combining ability، gene action، heritability and other genetic parameters in bread wheat under drought stress condition were evaluated using half diallel design. Nine wheat cultivars and 36 derived F1 assessed in a randomized complete block design with three replications in Shahid Bahonar University of Kerman research field in 2013. Evaluated genotypes showed high diversity for all traits. General combining ability (GCA) was highly significant for all traits and specific combining ability (SCA) was significant for all traits except stem angel. These results show the additive and non-additive effects on genetic control of these traits. Validity test of Hayman model showed the effect of epistasis on genetic control of all traits apart from stem angle. This dilemma makes breeding more obscure for these traits. Narrow heritability varied from 0. 06 for flag leaf angel to 0. 49 for stem angel. High Baker ratio، absent of epistasis and high narrow heritability show high response to selection in breeding programs for stem angel. Selection during segregation generation would be effective for this trait. Non-additive effects (dominant and epistasis) were highly important in genetic control of other traits. Bulk، single seed descent and double haploid methods are appropriate for these traits in breeding programs.

A partial set of diallel crosses conducted among seven bread wheat genotypes contain (Gasspard،M86-4،M86-6،DN-11،WS82-9 and M86-12) along with 21 hybrid، based on randomized complete block design (RCBD) with three replication were evaluated. The experiment was accomplished in a research field of agriculture and natural research center of Tehran Province in 2012-2013 in order to study genetic analysis of yield and some related traits like، grain number spike-1، plant height، grain yield،، kernel weight-1، peduncle length-1 non -fertile floret، and day to flowering. Significant (p≤0. 0l) differences were observed among genotypes for all the studied traits. The fitness of an additive-dominance model was accompanying for traits like: kernel weight، grain yield. However، for the remaining trait، when one parent was excluded، the assumptions were fulfill. Based on the estimates of average degree of dominance and result of graphical analysis gene action for the، plant height، kernel weight and number of non -fertile floret in the spike was partial dominance، while days to heading and grain yield were controlled by over dominance gen action. Broad -sense heritability estimates ranged from 51 Percent for grain yield to 75 Percent for days to heading. Narrows- sense heritability estimates ranged from 28 Percent for (grain yield to 48 Percent for grain number. Spike-1. The WS82-9 had the highest GCA effects for، grain yield،، kernel weight plant height and peduncle length and the DN-11 line and Chamran cultivar had the highest positive and significant differences for the number of grain spike-1 and kernel weight respectively. So this parents can be used for identifications and introduction of new bread wheat varieties in breeding programs. The hybridization of the 2 × 1 and 3 × 5 showed the highest values (sij) for number of grains per spike-1 and kernel weight-1 (yield two important components) respectively.

In order to estimate heritability، heterosis، general and specific combining ability and relationships between them in traits of fruit number per plant، days to the first fruit harvest، yield per plant، average fruit weight and rind thickness، seven local populations of Iranian melon (‘Tashkandi’، ‘Khatouni’، ‘Garmak’، ‘Aran1’، ‘Mirpanji’، ‘Suski-e-Sabz’ and ‘Golpaygan’) were crossed using a complete diallel crosses design، Griffing’s method 1، Model I. Parents and all possible hybrids were evaluated in a randomized complete block design with three replications. Analysis of variance revealed high significant differences among F1 hybrids and their parentes for all studied traits. Therefore analysis of combining abilities showed that specific combining ability (SCA) for yield per plant was greater than general combining ability (GCA)، indicating the importance of non-additive genes controlling this character. General combining ability effects were significant for most parents in all the studied traits. High estimation of narrow sense heritability (h2ns) for the traits of fruit number per plant، fruit weight، days to the first fruit harvest and rind thickness (0. 83، 0. 82، 0. 79 and 0. 74، respectively) indicated low effects of environment on the expression of those traits and very important role of additive gene effects. High estimate of h2ns (0. 83) was found for fruit number per plant. High heterosis effect over the better parent was found for yield per plant (15. 78 percent)، therefore، it is suggested to apply both additive and non-additive genetic effects to develop superior hybrids in melons.

Partial diallel design can be used to investigate the general and specific combining ability, and heterosis. Combining ability and heterosis were studied in a 6×6 partial diallel cross to see the nature of gene action for fruit quality indices in cucumber (Cucumis sativus L.) during 2007 to 2009. Analysis of variance revealed highly significant differences among all the F1 hybrid means and their respective six parental values for all the traits examined. The mean squares of general combining ability (GCA) and specific combining ability (SCA) were also highly significant. SCA genetic variances were greater than GCA and more important for the seedcell size, showing the additive and non-additive gene action. Fruit color was controlled by additive type of gene action due to high GCA variances. Fruit shape and overall performance were controlled additively and non-additively due to high general combining ability. Line 605 and 118 were found to be the best general combiner and its utilization produced valuable hybrids with desirable SCA F1 hybrids.

Melon is an economically important crop and Iran is considered as its diversity center. To investigate gene action, heritability and number of effective factors for yield and related traits, six generations, namely: P1, P2, F1, F2, BC1, and BC2 of two crosses of Mirpanji × Tashkandi and Mirpanji × Abasali were produced and evaluated in the spring of 2008, applyig a complete block design of three replications. Significant differences were observed among generations for all the traits. In Mirpanji × Tashkandi, a positive significant cross heterosis over the more dominant parent was found for yield as well as for the acceptable yield (13.76 and 27.34% respectively). Estimates of gene effects as based upon a six-parameter model (according to Mather and Jinks in Mirpanji × Tashkandi cross) showed that a simple additive-dominance model is adequate for the evaluated characteristic except for days to maturity and for fruit length. Both additive and dominance gene effects were important in the governing and acceptable yields in Mirpanji × Tashkandi cross, while epistatic genetic effects were not important. Chi square and Joint Scaling Tests in Mirpanji × Abasali cross indicated that a simple additive-dominance model was not adequate for the evaluated characteristic, while epistatic genetic effects did prove their importance.

Combining ability and heterosis were studied in a 6×6 partial diallel cross during 2007-2009 to see the nature of gene action in cucumber (Cucumis sativus L.). Analysis of variance revealed high significant differences among all the F1 hybrid means and among their respective six parental values for all the traits examined. The mean squares attributed to General Combining Ability (GCA) and Specific Combining Ability (SCA) were also highly significant. SCA genetic variances were greater than those of GCA and more important for the traits of Marketable Yield as well as Simple Weight Index, showing the dominance of non-additive gene action. Early yield and nonmarketable yield were controlled by additive and non-additive type of gene action due to high GCA variances. Line 504 with its bearing of high general and specific combining ability is finally found desirable regarding cucumber hybrid seed production and therefore is recommended.

Arab horse is one of the popular pure breed in Iran that is registered by World Arabian Horse Organization (WA. H. O.). In this research 13 conformation traits were studied on a random sample of the Iranian Arab horses. Animal model with Derivative Free Restricted Maximum Likelihood (DF-REML) approach and DFREML software were used to estimate variance components of traits. Mean of the inbreeding coefficient for the population under study was 2. 12 percentage. The inbreeding coefficient of each horse was considered as a covariate. The effect of inbreeding on the whithers height (P<0. 01)، mid body، croup height and fore and back canon bones circumference was significant (P<0. 05). The lowest and highest heritability were equal to (0. 050 ± 0. 008) and (0. 614 ± 0. 087) and related to neck length and croup height respectively. This research was done at Islamic Azad University، Ghaemshahr Branch in (2007).