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Seedling Age and Fertilization Affect Susceptibility of Loblolly Pine to Fusiform Rust. S. J. Rowan, Principal Research Plant Pathologist, U. S. Department of Agriculture, Southeastern Forest Experiment Station, Forestry Sciences Laboratory, Carlton Street, Athens, GA 30602; Klaus Steinbeck, Associate Professor, School of Forest Resources, University of Georgia, Athens, GA 30602. Phytopathology 67:242-246. Accepted for publication 2 September 1976. Copyright 1977 The American Phytopathological Society, 3340 Pilot Knob Road, St. Paul, MN 55121. All rights reserved.. DOI: 10.1094/Phyto-67-242.

The susceptibility of Pinus taeda seedlings to infection by Cronartium fusiforme increased with seedling age at the time of artificial inoculation. Fertilization with N and with P also influenced the infection rate, as did all possible interactions between seedling age at inoculation and the N and P treatments. Potassium supply had no direct effect on seedling susceptibility. Foliar levels of P, K, Mg, Mn, and Zn were not related to infection rate. Gall length, seedling susceptibility to the disease, and the number of lateral branches were correlated with seedling growth rate. Seedlings grew best when 300 μg/ml of N and 75 μg/ml of P were supplied in nutrient solution. Symptoms of the disease developed earliest on seedlings supplied with the optimum amount of N and P and inoculated at 8 wk of age.

Additional keywords: tree disease, seedling growth rate, disease development.