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Research.

Evaluating Fusiform Rust Symptoms on Greenhouse-Grown Slash Pine Seedlings to Predict Field Resistance. S. M. De Souza, Graduate Research Assistant, Department of Forestry, University of Florida, Gainesville 32611. T. L. White, R. A. Schmidt, C. H. Young, and R. L. Anderson. Associate Professor, Professor, Department of Forestry, University of Florida, Gainesville 32611; and Biological Technician, and Plant Pathologist and Manager, Resistance Screening Center, USDA Forest Service, Asheville, NC 28802. Plant Dis. 74:969-974. Accepted for publication 8 May 1990. Copyright 1990 The American Phytopathological Society. DOI: 10.1094/PD-74-0969.

Twenty-two fusiform rust traits (symptoms) were evaluated in greenhouse tests on slash pine seedlings for their usefulness in predicting rust resistance in the field. Seeds from five to 20 open-pollinated parents of known field rust resistance were mixed to obtain resistant, intermediate, and susceptible seed lots for inoculation. Seedlings from these seed lots were screened in 12 greenhouse tests (4 wk in each of three seasons). Logistic transformation of binomial traits was used to reduce seed lot × week and seed lot × season interactions. After transformation, all traits except medium gall size consistently ranked seed lots among weeks and seasons of inoculation and show promise for inclusion in a quantitative selection index for evaluating resistance in the field. Four traits—short galls, typical gall form, galls and adventitious shoots, and number of adventitious shoots—are the most promising because, in addition to giving consistent rankings, they were linearly related to field progeny test breeding values and could be measured on one gall per seedling.