VIEW ARTICLE

Resistance

Somaclonal Variation in Eastern Cottonwood for Race-Specific Partial Resistance to Leaf Rust Disease. C. S. Prakash, Assistant professor, School of Agriculture and Home Economics, Tuskegee University, Tuskegee, AL 36088; B. A. Thielges, Chairman, Department of Forestry, University of Kentucky, Lexington 40546-0073. Phytopathology 79:805-808. Accepted for publication 16 February 1989. Copyright 1989 The American Phytopathological Society. DOI: 10.1094/Phyto-79-805.

Forty eastern cottonwood (Populus deltoides) plants, derived by leaf callus regeneration in vitro (somaclones), were tested for their reaction to two races of Melampsora medusae, using the leaf disk assay. Most somaclones had leaf rust reactions similar to those of the parent, but some were more, or less, resistant than the parent. A significant interaction between somaclone and race was observed for two traits, latent period and uredinial number; thus the somaclonal variation for leaf rust resistance was of a race-specific nature. Somaclones as a group exhibited a longer latent period relative to the parental genotype, but complete resistance was not observed in any of the somaclones. If field studies confirm these laboratory observations, then somaclonal variation may be useful to increase the partial resistance (longer latent period and lower infection frequency) in eastern cottonwood to leaf rust and also may be used to produce congenic lines to facilitate studies on mechanisms of host-pathogen interaction.