EIP-AGRI Focus Group on IPM Brassica: Minipaper 6 - Identifying and utilising sources of host plant resistance as a key component of future IPM strategies

In wild species, host plant resistance is often a key factor limiting pest populations. However, in the last century the ‘green revolution’ enabled the breeding of crops with high yield under agronomic conditions in which plants have access to sufficient nutrients and water and where pests, diseases and weeds were controlled effectively by agrochemicals or other means. Other factors such as crop quality, including good physical appearance, were also critically important. However, despite the widespread use of pesticides, pests and diseases and competition from weeds are still responsible for
billions of pounds worth of crop losses each year. Chemical control is confounded by a number of factors, including loss of efficacy due to the evolution of resistance in the target species (e.g. the moth Plutella xylostella and the aphid Myzus persicae are reported to have gained resistance to the majority of insecticides in use, and likewise blackgrass (Alopecurus myosuroides) has developed resistance to a wide range of herbicides), legislative removal on the basis of environmental concerns, the slow development of the next generation of pesticides, incomplete protection when pesticides are used due to variation in coverage of a crop, and limited availability to farmers in many parts of the world. In addition, pesticide application represents an additional cost to farmers. The number of pests that threaten crops is also likely to be altered by increased pest ranges predicted as a result of climate change (e.g. P. xylostella currently does not overwinter successfully in the UK and most damage is due to migration of moths from continental Europe and North Africa, but warmer winters may enable it to do so and hence increase the number of generations produced in a season). Many of these issues could be overcome by the incorporation of genetic resistance into cultivars and so this has become a major activity in most crop breeding programmes.