عنوان مقاله [English]
Drought is one of the environmental factors which damages tobacco production in many countries as well as in Iran. Therefore, breeding for tolerance to drought stress has taken a major attention in Iran. In the present investigation, combining ability, gene action and genetic analysis of four characteristics including nicotine and sugar contents and nitrogen and K2O percent were studied in five Virginia varieties of tobacco and their ten F2 populations. The materials were evaluated in two different experiments using a Randomized Completely Block Design (RCBD) with three replications at two drought stress and normal irrigation conditions in 2006 at the Rasht Tobacco Research Center. Analysis of variance revealed significant differences among genotypes for all of the traits. Diallel cross analysis was conducted using model II of method II of Griffing. General combining ability (GCA) and the specific combining ability (SCA) effects were highly significant for all the traits in both conditions. The results showed that the non-additive genetic variance had an important role in controlling nicotine and sugar content in both conditions, while, for K2O percent in non-stress condition and nitrogen percent in stress condition, the additive variance was more important than dominance variance. K394 variety in non- drought stress condition and Coker254 in stress condition were introduced as the best parents to reduce nicotine content. Coker347 in both drought stress and non-drought stress conditions was found as the best cultivar to increase sugar content. The best hybrid for decreasing nicotine content was known in both drought stress and non-drought stress conditions of Coker347×Coker254. The best hybrid for increasing sugar content in non-drought stress condition belonged to Coker347×VE1, while, no hybrids was identified with high sugar content in drought stress condition. Hayman method was also used for graphical and genetical analysis of nicotine content and K2O percent in both conditions. Graphical analysis results showed that the over dominance genetic effects were existed for nicotine in both conditions.