The inheritance of resistance to isolates of Fusarium oxysporum var. nicotianae in burley tobacco

The Inheritance of Resistance to Isolates of Fusarium oxysporum var. nicotianae in burley Tobacco. (Under the direction of Creighton Lee Gupton). The objectives of this study were: (1) to determine the mode of inheritance of resistance in burley tobacco when using individual isolates of Fusarium oxysporum and (2) to estimate the genetic parameters conditioning resistance. Five burley tobacco varieties which range from highly resistant to susceptible were crossed in a diallel scheme to provide the genetic material for the study. Plants were subjectively evaluated for their disease reaction as six-week old seedlings in the greenhouse. The population means of the P₁, P₂, F₁, F₂, P₁F₁ and P₂F₁ generations of each cross were subjected to a generation means analysis to determine the genetic effects involved in resistance to the Fusarium isolates. The F₁ means were also evaluated for their general and specific combining ability. Although a statistical difference in virulence was found among the isolates, and at least two physiological races were represented among them, the mode of inheritance and genetic effects for resistance appeared to be very similar for each isolate. Results indicated that resistance of burley tobacco to the Fusarium isolates used in this study was quantitatively inherited and that general combining ability and additive gene effects were of major importance. Dominance and epistatic effects were also important in some populations and isolate combinations. It was concluded that the tobacco breeder can effectively use a mixture of Fusarium isolates when breeding for Fusarium wilt resistance. The breeding program should be designed to accumulate genes for resistance into pure lines since genetic effects are predominately additive.