Pest and disease management in organic farming: implications and inspirations for plant breeding

Summary

The co-evolution of plants with their pests and diseases is a major driving force in evolution in nature. As a consequence, many pests and pathogens have multiple functions involved in survival on host populations. As a result of this continuous co-evolution, plant pests and pathogens have been selected for high reproduction rates, because of the low probability of an individual being able to find or infect a compatible host plant. For their part, host plants in natural ecosystems are often interspersed among other plant species and show wide and changing variation among individuals for genes affecting specific or non-specific resistance to each of the many pathogens that may attack them. Throughout the plant world there are dynamic and unstable equilibria between hosts and pathogens that are easily perturbed. A major form of perturbation is agriculture, particularly in the form of monoculture, which creates massive exposure of a single host genotype to the pathogen population, raising, by orders of magnitude, the probability of successful infection by individual spores or pests and creating an opportunity for immense epidemics. Such a fundamental ecological shift is countered by either a technological response (breeding resistant varieties or developing interventions such as pesticides) or by mimicking or building on natural systems (diversifying host stands). The view of organic agriculture is that the greater holism of the second approach should make more tools available on the host side of the co-evolution while avoiding the risks associated with a more linear, technological approach. We begin this chapter with two case studies that exemplify the central importance of plant diversity for plant protection. We then briefly review the principles and practices of plant protection in organic agriculture. With this context laid out, we next turn to some key questions that are directly related to plant breeding for organic plant protection: What are the target areas of organic plant protection for breeding, i.e., what should be the priorities of organic plant breeding? What are suitable breeding goals for organic plant protection? Which breeding approaches can be used to directly target pests and diseases? What are possible approaches of plant breeding that indirectly contribute to plant protection? And finally, what are suitable selection strategies from the specific perspective of organic plant protection?