Field and Greenhouse Analysis of Variation for Disease Resistance in Tobacco Somaclones

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Abstract
A total of 854 somaclones of two flue-cured tobacco cultivars were generated from protoplast cultures, and their progeny analyzed in greenhouse and field tests for yield, leaf chemistry, and resistance to black shank, bacterial wilt, tobacco mosaic virus, and root knot (Meloidogyne incognita). Under the culture conditions established in this study, approximately 55% of the somaclones were not self-fertile. Progeny of the somaclones had normal phenotype and did not differ significantly from the parent cultivars in yield and leaf chemistry. Significant variation was found in resistance to black shank and bacterial wilt, two diseases for which the parent cultivars have low levels of resistance. The variation that was observed in response to these diseases depended on the disease as well as the genotype of the parent. Somaclones of cultivar NC2326 were similar to the parent cultivar in black shank resistance, but many had greater resistance to bacterial wilt than did NC2326. Most cultivar Coker 319 somaclones were more susceptible than the parent cultivar to black shank but had bacterial wilt resistance similar to that Coker 319. Variation in black shank and bacterial wilt resistance was slight, and few somaclones had responses equivalent to those of the susceptible and resistant control cultivars. However, conditions used in this study reduced the amount of potential variation. No somaclones were identified with resistance to tobacco mosac virus or M. incognita. We conclude that genetic variation occurred in the somaclones, that the magnitude of variation was slight, and that the variation depended on both the genotype of the parent cultivar and the trait.