Developing blister rust resistance in white pines

Abstract

After a century since introduction to North America from Europe, white pine blister rust, caused by Cronartium ribicola J.C. Fisch., is recognized as one of the catastrophic plant disease epidemics in history. It has not yet stabilized and continues to spread and intensify. Its nine native white pine hosts comprise major timber producers, important watershed protectors, keystone ecological species, and the oldest trees on earth. All are highly susceptible and some have been damaged severely in parts of their native range, as well as where they have been planted as exotics. Resistance, the most promising approach to control, requires understanding of genetic interactions between hosts and pathogen, a quest that has been ongoing for half a century. Unlike other hosts of spectacular exotic diseases, such as chestnut blight [caused by Cryphonectria pamsitica (Murrill) M.E. Barr] and dutch elm disease [caused by Ophiostoma ulmi (Buisman) Nannf.], white pines (Pinus.) exhibit a surprising number of resistance mechanisms to blister rust, if at only low frequencies. There are three main kinds:

Major gene resistance (MGR), controlled by dominant genes conditioning hypersensitive necrosis in needles, the primary infection courts, occur in at least three species. But MGR is not always as simple as it appears; epistatic interactions that affect penetrance and even dominance relationships of Mendelian genes exist in some genetic backgrounds. Slow rusting resistance (SRR), is only partial resistance, and ranges from very strong to weak. More complexly inherited, it is expressed by lower infection frequency in different trees and families, and by different kinds of bark reactions that abort infections after they establish in stem tissues. Ontogenetic resistance (OGR) comprises factors that confer resistance to some adult trees. It is genotype specific. OGR is very strong, but the least understood and probably most difficult mechanism to develop.

Citation

Kinloch Jr., Bohun B. 2000. Developing blister rust resistance in white pines. HortTechnology 10(3): p. 546