Selection and breeding for insect and disease resistance

Pest and disease resistance has been an essential part of crop breeding for many years, but has only had marginal impact in tree breeding to date. Crop varieties are domesticated and their continued cultivation depends on continuous breeding programmes for insect, disease and virus resistance, since large-scale monocultures are generally more susceptible to variable pathogens. Forest trees are mainly wild, undomesticated, outbred organisms and their natural populations retain a wide genetic diversity that helps them resist insect pests and pathogens. In addition, the genetic control of insect pest and disease resistance is sophisticated and probably more complex than for annual crops. Moreover, conventional tree selection and breeding for insect and disease resistance requires complex and lengthy laboratory and field tests, especially since resistance patterns may change from young to adult trees.

Over the past 20 years, tree breeding programmes have been reduced worldwide and now focus on a limited number of species and traits. However, since the risk of introducing new pests is likely to increase in the future, insect and disease resistant breeding programmes may be particularly important for several large-scale or valuable commercial plantations.

Pest resistance breeding may be a technical option in large-scale or valuable commercial plantations if there: 

• are few silvicultural options to mitigate losses to insect pests and diseases;
• are no alternative species;
• is an increasing risk of introductions of exotic pests.