Resistant Responses in Loblolly Pine to Spray and Injection Inoculations with Cronartium quercuum f. sp. fusiforme. E. G. Kuhlman, Research Plant Pathologist, USDA Forest Service, Southeastern Forest Experiment Station, Green Street, Athens, GA 30602. H. R. Powers, and W. D. Pepper. Research Plant Pathologist, and Biometrician, USDA Forest Service, Southeastern Forest Experiment Station, Green Street, Athens, GA 30602. Plant Dis. 74:1013-1015. Accepted for publication 18 June 1990. 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, 1990. DOI: 10.1094/PD-74-1013.

The responses of 6-wk-old loblolly pine seedlings from resistant families to concentrated basidiospore spray (CBS) system inoculations with Cronartium quercuum f. sp. fusiforme indicated the relative susceptibility of branches of those seedlings at age 2 yr to hypodermic inoculations with basidiospores. Seedlings with no stem symptoms or with symnos (purple stem spots with no stem swelling) after CBS inoculations were most resistant to hypodermic inoculations. Seedlings with no stem symptoms could be considered disease escapes, but they were as resistant to hypodermic inoculations as those with symnos. Seedlings with small or large galls after CBS inoculations were equally susceptible to hypodermic inoculations. Infection increased with an increasing inoculum density from 3 × 10³ to 3 × 10⁵ basidiospores per milliliter. However, an inoculum density of 3 × 10⁶ basidiospores did not produce more infections of susceptible loblolly pines nor more frequent aecial sporulation than did 3 × 10⁵ spores. Aecia occurred equally frequently in the 3 × 10⁵ and 3 × 10⁶ treatments but were more frequent after 2 yr than 1 yr.

Keyword(s): fusiform rust.