For the purpose of graphical analysis and estimation of genetic parameters related to yield and its components, six tobacco genotypes was crossed in half -diallel mating design. In this study, the F₂ progenies and their parents were evaluated in a randomized complete block design with three replications. The results of analysis of variance indicated a significant difference between genotypes for plant height, leaf number, leaf dry weight and leaf fresh weight. Hayman graphical method was utilized for analysis of data. Diallel analysis indicated existence of an additive and dominant actions in inheritance of all studied traits. Traits including plant height, leaf number, leaf length and width, stem diameter, internode distance and leaf dry weight possessed greater additive effects meanwhile in the leaf weight the dominance effect was greater. The additive gene action detected for leaf dry weight (yield) manifested the influence of selection methods in breeding of this trait. Due to the fact that the fresh weight of the leaf was controlled by dominance effects, so hybrid-based methods are effective in modifying this trait. Also, additive and dominance gene action were contributed in heritability of yield, plant height and number of leaves. Regarding the mean values of dominance degree and results of graphical analysis, the gene action for leaf fresh weight was over-domnance and so, the heterosis phenomenon could be used to increase and improve this trait. For the traits including plant height, leaf number and yield, the gene action type was relative dominance.
 

The diallel mating design is an important tool used by plant breeding programs to obtain information on trait inheritance. Knowledge of gene action, heritability and genetic advance from selection is a prerequisite for starting a breeding program for developing varieties of maize. Five maize S₇ lines and their F₂ progenies were studied in a 5 × 5 half-diallel crossing design to evaluate the gene action and the heritability of biochemical and physiological traits. Parents and their F₂ hybrids were planted in a randomized complete block design with three replications at the Research Farm of Graduate University of Advanced Technology (Kerman, Iran) in 2017 cropping year, and chlorophyll (Chl), proline, protein, carotenoid and reducing sugars traits were evaluated. Analysis of variance showed significant differences among genotypes for the studied traits at 1% probability level. The graphical results of Hayman's analysis showed the role of over-dominance genes effects in controlling proline content, sugars content, Chl a, Chl b, total Chl and carotenoids traits whiles the protein content trait was controlled by the incomplete dominance of genes. The narrow-sense heritability for carotenoid and proline content traits were 0.14, for protein content was 0.44 and for other traits were varaied in this range. The results of this study showed that the use of heterozygosity and the production of hybrid varieties can be used to breeding traits such as proline content, sugars content, Chl a, Chl b, total Chl and carotenoids. However, for breeding of protein content, use of both methods (selection and production of hybrid) are proposed.