Metabolomic Fingerprinting of Potato Cultivars Differing in Susceptibility to Spongospora subterranea f. sp. subterranea Root Infection.

Plants defend themselves from pathogens by producing bioactive defense chemicals. The biochemical mechanisms relating to quantitative resistance of potato to root infection by Spongospora subterranea f. sp. subterranea (Sss) are, however, not understood, and are not efficiently utilized in potato breeding programs. Untargeted metabolomics using ultra-performance liquid chromatography coupled with quadrupole time-of-flight mass spectrometry (UPLC-Q-TOF/MS) was used to elucidate the biochemical mechanisms of susceptibility to Sss root infection. Potato roots and root exudate metabolic profiles of five tolerant cultivars were compared with those of five susceptible cultivars, following Sss inoculation, to identify tolerance-related metabolites. Comparison of the relative metabolite abundance of tolerant versus susceptible cultivars revealed contrasting responses to Sss infection. Metabolites belonging to amino acids, organic acids, fatty acids, phenolics, and sugars, as well as well-known cell wall thickening compounds were putatively identified and were especially abundant in the tolerant cultivars relative to the susceptible cultivars. Metabolites known to activate plant secondary defense metabolism were significantly increased in the tolerant cultivars compared to susceptible cultivars following Sss inoculation. Root-exuded compounds belonging to the chemical class of phenolics were also found in abundance in the tolerant cultivars compared to susceptible cultivars. This study illustrated that Sss infection of potato roots leads to differential expression of metabolites in tolerant and susceptible potato cultivars.

Metabolomes of Potato Root Exudates: Compounds That Stimulate Resting Spore Germination of the Soil-Borne Pathogen Spongospora subterranea.

Root exudation has importance in soil chemical ecology influencing rhizosphere microbiota. Prior studies reported root exudates from host and nonhost plants stimulated resting spore germination of Spongospora subterranea, the powdery scab pathogen of potato, but the identities of stimulatory compounds were unknown. This study showed that potato root exudates stimulated S. subterranea resting spore germination, releasing more zoospores at an earlier time than the control. We detected 24 low molecular weight organic compounds within potato root exudates and identified specific amino acids, sugars, organic acids, and other compounds that were stimulatory to S. subterranea resting spore germination. Given that several stimulatory compounds are commonly found in exudates of diverse plant species, we support observations of nonhost-specific stimulation. We provide knowledge of S. subterranea resting spore biology and chemical ecology that may be useful in formulating new disease management strategies.

Systemic resistance induced by Bacillus lipopeptides in Beta vulgaris reduces infection by the rhizomania disease vector Polymyxa betae.

The control of rhizomania, one of the most important diseases of sugar beet caused by the Beet necrotic yellow vein virus, remains limited to varietal resistance. In this study, we investigated the putative action of Bacillus amylolequifaciens lipopeptides in achieving rhizomania biocontrol through the control of the virus vector Polymyxa betae. Some lipopeptides that are produced by bacteria, especially by plant growth-promoting rhizobacteria, have been found to induce systemic resistance in plants. We tested the impact of the elicitation of systemic resistance in sugar beet through lipopeptides on infection by P. betae. Lipopeptides were shown to effectively induce systemic resistance in both the roots and leaves of sugar beet, resulting in a significant reduction in P. betae infection. This article provides the first evidence that induced systemic resistance can reduce infection of sugar beet by P. betae.

Arabidopsis thaliana, a new tool to investigate Polymyxa betae-host interactions.

Little is known about the genome of Polymyxa betae and its interactions with sugar beet, due partly to the obligate nature of the protist and the patents on Beta vulgaris sequences. The identification of an ecotype of Arabidopsis thaliana compatible with the protist would help to improve this knowledge. The infection and development of P. betae in 14 worldwide ecotypes of A. thaliana were studied. The detection of plasmodia and resting spores and the production of zoospores in the roots of A. thaliana were obtained in three bioassays, using automatic immersion systems and individual glass tubes. Detection was done using molecular detection and microscopy. Compatible interactions were established between 13 A. thaliana ecotypes of the 14 that were tested and the monosporosoric Belgian strain of P. betae, A26-41. The ecotype Cvi-0 (N1096), from the Cape Verde Islands, was the most compatible with the protist. This ecotype is also susceptible to Plasmodiophora brassicae, another plasmodiophorid. Polymyxa betae infection in A. thaliana was relatively very low compared with B. vulgaris, but every stage of the life cycle of the protist was present. The spore-forming phase was promoted at the expense of the sporangial phase, probably caused by the stress of this new environment. In addition, the protist revealed a new phenotype. This new model study will allow molecular tools available for A. thaliana to be used in order to gain a better understanding of the P. betae-plant interaction during the spore-forming phase.