In vitro selection of Nicotiana sylvestris variants with limited resistance to TMV

Haploid tobacco (Nicotiana sylvestris) plants were inoculated with a yellow strain of tobacco mosaic virus (TMV-Flavum) and then exposed to 500 rads of acute gamma radiation. Leaf strips cultured on callus-inducing medium yielded two types of colonies: 1) yellow, virus-infected and 2) green, apparently healthy. Of the 3210 calli scored, approximately 5% were virus-free, and after regeneration, 0.2% were resistant at the plant stage. Later, adult plants, both TMV-resistant and TMV-susceptible, produced self-fertile, diploid flowers. Both seedling progeny and rooted cuttings from resistant stock plants showed resistance to TMV infection. This resistance was characterized by restricted virus multiplication and movement within the infected plant resulting in a 3–8 week delay in symptom expression.Journal Paper No. 10138 of the Michigan Agricultural Experiment Station.This work was supported in part by U.S.D.A. grant no. 79-59-2261-1-1-351-1.We thank Drs. M. Daub, R. Griesbach, and J. Hunsperger for helpful suggestions.The excellent technical assistance of Ms. Brenda Floyd and Sara Stadt is acknowledged.