Recognition and understanding the genetic control of traits, combining ability and genetic structure are directly related to the success of breeding programs. For this purpose, a 7 × 7 one-way DIALLEL design was conducted in a randomized complete block design with three replications. The measured traits were included plant height, height to the first capsule, number of days to 50% and 90% of flowering, number of capsules per plant, number of seeds per capsule, number of days to physiological ripening, number of branches, leaves number and length, 1000-seeds weight, capsule weight, length and width, chlorophyll a, b and total chlorophyll, biological andeconomic yields, harvest index, oil and protein percentage. ANALYSIS of variance showed that there was a significant difference between genotypes and DIALLEL ANALYSIS showed that the additive variance of all traits and dominant variance of all traits except height to the first fruit-bearing capsule were significant. The oltan cultivar was the best and Ardestan genotype was the worst genotype in terms of general combining ability. Sabzevar×TS-3 and Sirjan×Fars were the best hybrids in most traits. The general heritability was between 0.90 to 0.96 for biologic yield and number of branches, respectively and narrow heritability was between 0.36 to 0.91 for the number of branches and harvest index, respectively. The ANALYSIS of variance by Hayman method confirmed the results of Griffing ANALYSIS.

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.

In order to determining and identification of the nature of gene action in inheritance of different traits, 56 genotypes (crosses and reciprocals) developed from DIALLEL crosses of eight maize inbred lines along with parents were evaluated for important quantitative traits using randomized compelet block design with three replications in the Experimental Field Station of Seed and Plant Improvement Institute, in 2005 cropping season. DIALLEL ANALYSIS revealed the presence of over-dominance gene action in controlling grain yield, kernel number per ear row, kernel depth, ear length, plant height. Genes with partial dominance action were revealed in controlling number of rows per ear, numer of leaves and days to tasseling, while genes controlling 300 kernel weight and ear diameter showed dominant effects. Graphic ANALYSIS showed that for early reproduction stage, and increasing the grain yield, member of rows per ear and kernel number per row, length and diameter of ear, leaf number, plant height, dominant genes ware involved, while, for 300 kernels weight, recessive genes were effective.

Blast disease is considered as the most serious disease of rice throughout the world. To genetically analyze leaf blast resistance, five rice cultivars namely Khazar, Hashemi, Kadoos, Fuji and Rashti were crossed together in the framework of a defective half DIALLEL design. Parents and the resulting lines were cultured in greenhouse in the form of a randomized complete block design. Following inoculation with five blast isolates of: IA-66, IA-38, IA-79, IA-181, and IA-l77, such characteristics as number of blast lesions on the leaf, percent of leaf infection area as well as lesion size were evaluated using international standard method for evaluation of blast disease (S.E.S). The results recorded from the ANALYSIS of variance indicated that there exist significant differences among genotypes. The significance of general combining ability, specific combining ability and also the relationship between general and specific combining ability indicated the effect (simultaneous) effect of additive and non- additive gene action (with a greater share going to additive gene action). In the control of these characteristics a dominant gene also plays its role. High narrow and broad sense heritabilities were reported for all these characteristics. Considering the high heritability in these characteristics and the additive effect of the resistance genes, it can be concluded that Khazar, Kadoos and Fuji resulting lines could suitably be used for cultivars for increasing the resistance against the above mentioned blast disease agents.

Genetic control of infection type of stripe rust was studied in a half-DIALLEL design using six wheat varieties, Tiritea (a susceptible control), Tancred, Kotare, Otane, Karama, and Briscard. These varieties and their 15 F1 DIALLEL hybrids were evaluated by three stripe rust pathotypes, 7E18A-, 38E0A+, and 134E134A+. For each pathotype a randomized complete block design was conducted with 21 treatments. Data for infection type were analyzed on the basis of Morley Jones, Waiter and Morton, Griffing, and Hayman's graphical methods. Positive and negative degrees of dominance were observed for every pathotype, indicating the host-pathogen interaction. Analyses of variance showed the importance of both additive and dominance genetic effects in controlling the infection type of stripe rust. However, the role of additive effects was more important than non-additive effects. Average of broad-sense and narrow-sense heritability estimates was 0.92 and 0.89, respectively. In the graphical ANALYSIS of Hayman, degree of dominance ranged from partial dominance to overdominance depending on the pathotype. Briscard, in all pathotypes, Karama in 7E18A- and 38E0A+and Kotare in 134E134A+, had mainly recessive genes. Significant negative geperal combining abilities(more resistance)were also obtained for Kotare in 7E18A-, for Briscard in 38E0A+,and for Briscard, Karama, and Kotare in 134E134A+.In conclusion, regarding the high heritability of infection type, it is possible to use the above mentioned varieties in breeding programs in order to reduce the infection type of stripe rust in wheat      

Bilateral DIALLEL crosses of eight rapeseed genotypes were used to graphically analyze and estimate of genetic parameters for agronomic and physiological characteristics. F1 along with their parents (64 genetypes) were planted in a randomized complete block design with three replications at Gorgan Agriculture Research Station, in 2019-2020. The results of ANALYSIS of variance showed that a and b components were significant for all traits. The results of the Jinks-Hayman test indicated that hypothesis of the genetic ANALYSIS were satisfied for pod length, number of pod per lateral branches, number of pods per plant and 1000-grain weight traits. ANALYSIS revealed significant values for D and H1 estimation for all traits, which indicated the existence of both additive and non-additive effects on genetic control of these traits. While the proportion of non-additive variance was higher than the additive effects for all traits, which was in agreement with high mean levels of the degree of dominance. The positive and significant sign of F confirmed that there are much more dominant alleles than recessive alleles in parents, regardless of whether they have a negative or positive effect. Based on Hayman graphical ANALYSIS, 1000-grain weight was influenced by the dominance of genes. Narrow-sense inheritance levels were low for all traits, which could indicate a greater impact of environmental and non-additive effects on their genetic control. The results showed that selection-based methods were not very effective in canola yield improving and production of hybrids and exploiting the effects of gene dominance is necessary.

Ten genotypes including six F1 progenies and their parents were grown in Kashmar Cotton Research Station in two separate experiments (non-stress and drought stress conditions), in a randomized complete block design with three replications. DIALLEL ANALYSIS was done based on Griffing’s method II for seed cotton yield, boll seed cotton weight, percentage of earliness, the number of bolls and height of plant. Results showed that the variance of genotypes was significant for boll seed cotton weight and height of plant in non-stress environment and for seed cotton yield and height of plant in stress condition. The effect of general combining ability of boll seed cotton weight and height of plant were significant in non-stress environment. Also it was significant for seed cotton yield and height of plant in drought condition. The effect of specific combining ability wasn’t significant for any trait. DIALLEL ANALYSIS showed that additive gene effect had an important role in controlling the mentioned traits. Combined DIALLEL ANALYSIS indicated that additive variance was important for seed cotton yield and height of plant. Broad sense heritability was high for all traits in both conditions, whereas narrow sense heritability varied from low to high in both conditions.