INHERITANCE OF PARTIAL RESISTANCE TO TOBACCO ETCH VIRUS AND TOBACCO VEIN MOTTLING VIRUS IN BURLEY TOBACCO CULTIVAR SOTA-6505

Tobacco etch virus (TEV) and tobacco vein mottling virus (TVMV) are se rious diseases of burley tobacco and are controlled most effectively b y use of resistant cultivars. The inheritance of resistance to TEV and TVMV in the burley 'tobacco cultivar Sota 6505 and allelism with othe r sources of potyvirus resistance were evaluated. Crosses were made be tween Sota 6505 and two susceptible burley tobacco cultivars, Ky 14 an d Va 528. Parental genotypes, F1, F2, and backcross generations to eac h of the parents were evaluated in randomized complete block designs f or TEV resistance at Waynesville, North Carolina, and Las Varas, Nayar it, Mexico, and for TVMV resistance at Laurel Springs, North Carolina, during 1988 and 1989. Crosses were also made between Sota 6505 and TE V- and TVMV-resistant cultivars Virgin A Mutant and Havana 307 to test for allelism. Resistant X resistant crosses were evaluated for TEV re sistance in a greenhouse in Raleigh, North Carolina. Plants were mecha nically inoculated in the field approximately 1 mo after transplanting and in the greenhouse 1 wk after transplanting. Disease severity data were collected at topping time in the field and 1 mo after transplant ing in the greenhouse. Chi-square goodness of fit tests were conducted , but simple Mendelian inheritance ratios did not fit the data for exp ression of resistance with either virus, possibly because of environme ntal effects. Generation means analysis showed that a simple additive- dominance model adequately described the data. Additivity was the majo r genetic effect, and there was no evidence of epistasis. The gene(s) controlling TEV resistance in Sota 6505 appears to be allelic to the v irus resistance gene(s) found in resistant cultivars Virgin A Mutant a nd Havana 307.