Strategies in modern agriculture aim to enhance harvest yields per acreage and to reduce pre-harvest and post-harvest losses caused by detrimental abiotic and biotic causes. The potential of that reflects an estimate 20–40% reduction of agricultural production worldwide that is taken by pests and diseases. Modern pest management strategies in crop plants include classical and molecular marker-based resistance breeding, genetic engineering of plant immunity and the use of chemicals as pesticides or strengtheners of plant health. While breeding strategies are time-consuming and harbor the problem of ‘linkage drag’ (transfer of undesirable traits that need to be removed after introgression of the desired trait by back-crossing), genetic engineering holds the potential of being reasonably fast and predictable in its consequences because of the targeted introduction of individual, heterologous traits into elite crop lines.
Sequencing of entire plant genomes, systematic plant transcriptome profiling and comprehensive genetic dissection of immune pathways in model plants (Arabidopsis thaliana, rice) has significantly enhanced our understanding of the mechanisms underlying microbial infection and plant immunity. The plant immune system consists of two evolutionarily linked branches. Recognition of invariant microbial surface patterns (pathogen or microbe-associated patterns; PAMP/MAMP) through plant pattern recognition receptors is referred to as PAMP-triggered immunity (PTI) and is the basis for broad-spectrum resistance of plants against host non-adapted microbial pathogens (i.e. all genetic variants of a given microbial species are unable to grow on a given plant species).
Novel insight into plant immunity and disease may now be turned into new tools to engineer durable, broad-spectrum plant disease resistance. This review highlights recent scientific discoveries in plant immunity and discusses their potential for enhancing plant immunity in crop plants with particular emphasis on immunity to bacterial and fungal infection. Saving the world’s food supply constitutes one of the major challenges of the future. As a complement to classical and molecular breeding technologies, novel strategies for biotechnological improvement of plant immunity aim at enhancing host recognition capacities for potential pathogens, at boosting the executive arsenal of plant immunity, and at interfering with virulence strategies employed by microbial pathogens. In addition, chemical and biological priming provides means for triggering plant defenses in a non-transgenic manner. Major advances in our understanding of the molecular basis of plant immunity and of microbial infection strategies have opened new ways for engineering durable disease resistance in crop plants that are highlighted in this review.