Genetic Variation and Heritability of Melampsora Leaf Rust Resistance in Eastern Cottonwood
Much variation in resistance to a Melampsora leaf rust was encountered in an eastern cottonwood provenance and progeny test at Wooster, Ohio. This test, one planting of the NC-99 Regional Cooperative Study, consists of 228 clones originating from 76 parent trees. Disease resistance was rated on a visual scale from 1 to 7. Differences in resistance among and within open-pollinated families were significant. There were no differences between ramets of the same clone. Pronounced differences in rust damage and its rate of progression were related to geographic location of the seed parent. Families derived from parent trees in Missouri and Illinois were more resistant than those from Ohio, Pennsylvania, and Indiana. Broad-sense heritability estimates for disease resistance were high (0.88-0.95). Ease of recognizing Melampsora-resistant phenotypes, strong genetic control of the trait, and advantages of vegetative propagation should contribute toward rapid, substantial improvement in rust resistance. Selection for resistance is compatible with selection for growth rate and form. Relative resistance may be a direct determinant of annual diameter growth. Forest Sci. 21:278-282.
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