Screening pea for resistance against a root rot complex on naturally infested field soil

Summary

Root and foot diseases severely impede pea (Pisum sativum) cultivation worldwide, and therefore a valuable protein source and important crop in low-input farming systems. Breeding lines with resistance against individual pathogens exist, but these resistances are often overcome by the interaction of multiple pathogens in the field. Moreover, resistance depends on the interactions between the plant associated microbial community and the host, and there is increasing evidence for the existence of genetic variation in the regulation of plant–microbe interactions that can be exploited by plant breeders. In order to acknowledge the entire native soil microbiome as a key element of plant resistance we designed a resistance screening experiment on naturally infested field soil. In a first step, DNA from diseased roots and rhizosphere soil from infected plants was isolated. Sequencing of the fungal ITS region in the roots and rhizosphere showed the presence of several know pea pathogens along putative antagonists. Subsequently, 261 pea lines were grown under controlled conditions and evaluated after three weeks. Along significant genotypic differences, moderate to high heritabilities could be revealed for root rot resistance and growth performance traits. Relating different resistance traits allowed to distinguish between highly susceptible, tolerant and resistant lines and between resistance at different time points in plant development (i.e. emergence and young plant stage). The evaluation of a subset of pea lines on two field sites with moderate and high root-rot potential, respectively, confirmed the resistance ranking obtained under controlled conditions. Furthermore, we used quantitative real-time PCR targeting selected fungal pathogen species to show that the pathogen DNA detected in the roots differs among resistant and susceptible pea genotypes, respectively. Our results indicate the replicability and usefulness of naturally infested field soil based screening systems. Such systems will allow to pursue research on plant-microbiome interactions and on the role specific pathogen species or potential beneficial microbes play in plant disease resistance.