Future trends

The field of plant resistance control is undergoing a very active and exciting period, during which major breakthroughs are being made. Increased availability of cloned R genes will permit their testing in different plant backgrounds. In contrast with the success in the production of insect- and virus-resistant crops, the production of fungi-resistant crops with commercially useful levels of resistance has not been achieved. However, it is likely that commercial introduction of fungi-resistant crops can be expected within 4–8 years.

In the same way that plant breeders are continually developing new varieties that contain the most effective combination of existing characteristics, there is a similar trend with transgenic crops. Many laboratories are experimenting with ‘pyramiding of genes’, which consists of the introduction of multiple genes conferring different characters. A good example of this is a potato line containing seven transgenes that will confer resistance to insects, fungi, virus, and will alter other phenotypic characteristics (Dunwell 2000).

Overexpression of signalling components that lie downstream of R genes is an interesting approach that is currently being tested. This may allow activation of only certain defence pathways and may avoid agronomic problems associated with constitutive activation of some R-mediated pathways (see Section Plant R genes). The use of antimicrobial peptides to engineer broad-spectrum resistance is a promising and powerful approach that will be used considerably in the near future.

The increased use of inducible promoters is another current trend to manipulate specific pathways or to express R genes in a much more controlled manner (Shen et al. 2000). Finally, in addition to the progress being made on the plant side of the equation, an understanding of the genetic make-up of pathogens and the critical genes involved in the pathogenesis process are expected to open new avenues in crop protection.