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Fertilizer-Induced Changes in Susceptibility to Fusiform Rust Vary Among Families of Slash and Loblolly Pine. S. J. Rowan, Principal Research Plant Pathologist, U.S. Department of Agriculture, Southeastern Forest Experiment Station, Forestry Sciences Laboratory, Carlton Street, Athens, GA 30602; Phytopathology 67:1280-1284. Accepted for publication 23 March 1977. Copyright 1977 The American Phytopathological Society, 3340 Pilot Knob Road, St. Paul, MN 55121. All rights reserved.. DOI: 10.1094/Phyto-67-1280.

Effects of fertilization on susceptibility (percent of seedlings infected) to fusiform rust (caused by Cronartium fusiforme) were observed in 11 artificially inoculated families of slash pine, and seven families and one geographic race of loblolly pine. Fertilization (N + P + K + Fe) increased the susceptibility of all families, but significant family fertilization interactions were found in both loblolly and slash pine. This finding implies that seedling susceptibility tests in tree improvement programs should include seedlings both fertilized and not fertilized prior to inoculation. The length of the shoot (the assumed infection court), when seedlings were inoculated 8 wk after emergence, was affected significantly by fertilization, family, and their interaction. Shoot length, however, was not correlated with the percentage of seedlings that became infected. Thus, susceptibility in young slash and loblolly pine seedlings is not strongly controlled by the size of the infection court.

Additional keywords: tree disease, tree improvement.