Diallel Crosses in Nicotiana tabacum 1

COMPARISONS of parent and F1 hybrid performance in tobacco are numerous in literature and a review of this early work was given by Ashton (1). The objective most previous studies has been to assess the amount of heterosis and to determine if it was sufficient to justify the use of F1 hybrids on a commercial scale. Even though tobacco is naturally self-fertilized, crossing can be accomplished with ease and seed yields are high. In some cases workers have advocated the use of F1 hybrids commercially, e.g., Bawolska et al. (2), however, most authors refer "fixing of heterosis" in later generations, e.g., Rave and Bolsunov (3). The resolution of the question of whether heterosis can be maintained only in the F1 generation, or whether transgressive segregates can be isolated in pure lines equal or superior to the F, depends upon the types of predominant gene action for each character in the population under study. Very little has been done to relate the amount of heterosis obtained in tobacco crosses with estimates of types or amount of genetic variability. As the first step in a program to obtain quantitative genetic information in fluecured tobacco and to relate this information to breeding methodology, the present experiment was planned with the following objectives: (1) to estimate the amount of heterosis and inbreeding depression in flue-cured tobacco crosses, (2) to test for differences between reciprocal F hybrids, (3) to obtain estimates of variances of general and specific combining ability, and (4) to measure the stability of general and specific effects with respect to environmental differences. The material used will form the foundation for extensive statistical genetic studies to determine more clearly the genetic mechanism governing the inheritance of a number of characters and their response to selection.