Indirect selection and clonal propagation of loblolly pine seedlings enhance resistance to fusiform rust

Abstract

A population of loblolly pine (Pinustaeda L.) seedlings without fusiform rust (Cronartiumquercuum (Berk.) Miyabe ex Shirai f.sp. fusiforme) galls was developed by controlled-cross matings of parent trees with known rust resistance, and subsequent screening of the seedling offspring through artificial inoculation. The seedlings without rust galls then entered a vegetative propagation system using rooted cuttings. A second round of rust testing by artificial inoculation, using a random sample of 20 clones from the program, revealed a high degree of rust resistance (4% galled) compared with that of seedlings from either a resistant control seedlot (50% galled) or a susceptible control seedlot (81% galled). This apparently high degree of rust resistance may be due to genetic effects, rooted cutting morphology, or both.