Selection and breeding for insect and disease resistance
Global status of research and applications
Although the results of most private research agencies are typically not well documented in the public domain, a substantial body of literature and activities are generated from publicly funded academic institutions or government research-oriented programmes. They primarily cover the following areas.
- Characterization of resistance - There are at least three types of resistance at the genetic level:
- total resistance, generally controlled by single genes, simple to identify, and thus amenable to genetic modification if the genes are available;
- partial resistance, variable among individuals, often under polygenic control, and very often used in both crop and tree breeding;
- ontogenetic resistance, which typically varies with physiological age of the tree; although little is known, it has important features for resistance management in forest trees.
- Inheritance. Inheritance is studied through the transmission of relative susceptibility or resistance from parents to offspring;
- Gene functioning. Molecular techniques and biotechnologies now facilitate the study of gene functioning in connection with insect and disease resistance.
Research on pest resistance is making use of new biotechnologies, but at the same time many field trials and long-term resistance breeding programmes have received reduced support or have been stopped altogether. Biotechnology, primarily with the use of genetic markers and genetic modification as research tools, has been applied, however pest resistance is marginal in the overall use of biotechnology in forestry (only 1% of reported activities). Recently, however, is the development of strategies by foresters and ecologists (using many of the principles that tree breeders have used for commercial pest and disease resistance breeding programmes) to identify and select resistant trees in natural forests for restoration purposes, usually after the introduction of some exotic insect pest or disease.