Exploring resistance to Aphanomyces cochlioides in sugar beet

Abstract

Sugar beet (Beta vulgaris L.) is one of the two main sources of sucrose, second only to sugar cane, accounting for nearly 30% of sugar production worldwide. The viability of the crop is threatened by the attack of pathogens that cause various diseases, resulting in severe yield losses. The oomycete Aphanomyces cochlioides is one of the most important root pathogens in sugar beet due to its worldwide distribution and the ability to induce infection at any stage of the sugar beet lifecycle, causing both seedling damping-off and chronic root rot on mature roots. During the early phase of sugar beet cultivation, the infection can be controlled by chemical seed treatments. However, no major control strategies are available for the disease management in later stages during the growing season. An increased knowledge of the sugar beet responses to pathogen infection is required to find effective solutions to control the disease. The focus of this study was to enhance our understanding of the host-pathogen interactions. We explored A. cochlioides infection rates in different sugar beet genotypes by using molecular tools and confocal microscopy and we identified significant differences in the pathogen biomass between partially resistant and susceptible lines. Potential differences in sugar beet responses to different A. cochlioides isolates were also investigated through a transcriptomics study. Furthermore, the transcriptome analysis revealed a potential significant role for oxygen peroxide (H2O2) and cell wall modification in the defense mechanisms during A. cochlioides invasion. Candidate defense-genes were identified in the set of up-regulated transcripts of partially resistant plants. Lastly, we studied differences in the genetic resistance to damping-off and chronic root rot and we identified the genomic position of regions (quantitative trait loci) associated with damping-off resistance. Overall, the results of our research represent a valuable source for future studies to improve resistance breeding against A. cochlioides.