Detection of interactions between the pea root rot pathogens Aphanomyces euteiches and Fusarium spp. using a multiplex qPCR assay
Willsey, T.L., Chatterton, S., Heynen, M., Erickson, A. (2018). Detection of interactions between the pea root rot pathogens Aphanomyces euteiches and Fusarium spp. using a multiplex qPCR assay. Plant Pathology, [online] 67(9), 1912-1923. http://dx.doi.org/10.1111/ppa.12895
Plain language summary
Root rot of peas can cause devastating losses in the field. This disease is usually associated with a number of pathogenic microorganisms, termed the pea root rot complex. When organisms are present together in the same habitat (roots), they can interact with each other in a number of different ways with different outcomes. They can compete for resources in the roots and negatively effect each other, or they can help each other colonize roots and effectively make disease worse when present together. Because plant pathogens are microorganisms, it can be difficult to distinguish them from each other and to determine how they are colonizing root tissue. Therefore, DNA barcodes were designed for each organism of interest that would allow for identification and quantification of invidividual pathogen numbers. A greenhouse trial was conducted to determine how 4 types of pathogens interacted with each other. In all cases, the presence of multiple microorganisms in a root system resulted in higher disease than when only one microorganism was present. The way that microorganisms colonized the roots also changed when multiple organisms were present. Some microorganisms acted as a gateway by allowing a non-pathogenic microorganism to enter root tissues. These results indicate that the impact of root rots will be higher when multiple microorganisms are present, and thus disease management strategies need to target the complex of pathogens. Breeding efforts for disease resistance to root rot pathogens will also need to focus on screening against multiple microorganisms.
Pea root rot complex (PRRC) describes a group of closely associated soilborne pathogens that cause root rot disease in field pea. Aphanomyces euteiches and several Fusarium spp. are the most prevalent and damaging microorganisms within this complex, although the impact of interspecific interactions on disease progression remains largely unexplored. Furthermore, a fast and reliable method of detecting and quantifying these pathogens is not currently available. The objectives of this experiment were to: (i) investigate the effect of microbial interactions on root rot severity in pea under greenhouse conditions; and (ii) characterize changes in colonization rates when multiple pathogens are present using qPCR. Seeds were exposed to three species of Fusarium and were planted into A. euteiches-infested soil in varying combinations. For each experimental treatment, an index of disease severity was used to visually rate disease symptoms. Additionally, two triplex quantitative PCR (qPCR) assays were designed to detect and quantify changes in pathogen population dynamics on the roots. Both assays demonstrated a high degree of sensitivity and efficiency. Results from two independent greenhouse trials indicated an increase in disease severity in the presence of multiple pathogen species compared to single inoculations. Specifically, roots infected with A. euteiches were more susceptible to fusarium root rot than those exposed only to Fusarium spp. These observations were confirmed by qPCR results, which revealed significant changes in colonization rates when multiple species were present. These findings suggest an increased risk of yield loss in regions where A. euteiches and Fusarium spp. co-occur.