Tolerance of Loblolly Pines to Fusiform Rust
Loblolly pines (Pinus taeda L.) that were 8 to 17 yr old tolerated one to three fusiform rust (Cronartium quercuum [Berk.] Miyabe ex Shirai f. sp. fusiforme) galls in their stems.Families with four or more galls in their stems lost 2.5% or more of the trees by age 17.In living trees with less than four stem galls, diameter growth was comparable to that of trees with no galls. Tolerance was indicated by the ability of loblolly pines to maintain the rust fungus in stems that had dbh's similar to asymptomatic trees on the same site.In plantations, the number of galls in the stem was generally one to two per infected tree.This was also true for mature trees (12 to 38 in. dbh) along the Natchez Trace Parkway.These trees have been infected with fusiform rust for nearly 100 yr.On the other hand, the presence of four or more stems galls seems to be a reliable indicator of mortality rather than tolerance.