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Resistance

Effect of Inoculum Density and Fertilization on Greenhouse Screening of Loblolly Pine Seedlings for Resistance to Fusiform Rust. S. D. Carson, New Zealand Forest Service, Forest Research Institute, Rotorua, New Zealand; C. H. Young, Resistance Screening Center, USDA Forest Service, 200 Weaver Boulevard, Asheville, NC 28804. Phytopathology 77:1186-1191. Accepted for publication 10 December 1986. This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological Society, 1987. DOI: 10.1094/Phyto-77-1186.

Loblolly pine (Pinus taeda) with resistance to fusiform rust caused by Cronartium quercuum f. sp. fusiforme is selected indirectly through controlled inoculation of greenhouse seedlings. Progeny of 29 half-sib families with known field resistance were inoculated using two inoculum densities under two fertilization regimes. Families were ranked on the basis of seven symptom types. Fertilization did not significantly alter family rankings for most symptom types. The exception, presence of galls, was more highly correlated with field resistance when seedlings received a high level of fertilization. Changes in inoculum density did not alter family rankings. Greenhouse screening appeared to be more reliable for selecting resistant families than for differentiating among moderately resistant and susceptible ones.