Phytophthora infestans is the causal agent of potato late blight. This pathogen is usually controlled by fungicides, but new European regulations have imposed changes in crop protection management that have led to a search for alternative control measures. The induction of plant defence responses by elicitors is a promising new strategy compatible with sustainable agriculture. This study investigated the effect of eliciting a defence response in potato against P. infestans using a formulation of the COS-OGA elicitor that combines cationic chitosan oligomers (COS) and anionic pectin oligomers (OGA). Trials were conducted under greenhouse conditions to assess the ability of COS-OGA to control P. infestans. The results showed that three foliar applications with this elicitor significantly increased potato protection against late blight in controlled conditions. The activation of potato defence genes was also evaluated by RT-qPCR during these trials. Two pathogenesis-related proteins, basic PR-1 and acidic PR-2, were rapidly and significantly upregulated by the elicitor treatment. Therefore, these results suggest that the COS-OGA elicitor increases the protection of potato against P. infestans and that this protection could be explained by an increase in the expression of potato defence genes rather than by biocide activity.
Polymyxa betae belongs to the Plasmodiophorida (Phytomyxea, Rhizaria). Here, we report the first draft genome sequence of a member of the Polymyxa genus, which includes two obligate root endoparasite species, vectors of important soilborne plant viruses.
The molecular interactions between Polymyxa betae, the protist vector of sugar beet viruses, Beet necrotic yellow vein virus (BNYVV), the causal agent of rhizomania, and Beta vulgaris have not been extensively studied. Here, the transmission of BNYVV to sugar beet by P. betae zoospores was optimized using genetically characterized organisms. Molecular interactions of aviruliferous and viruliferous protist infection on sugar beet were highlighted by transcriptomic analysis. P. betae alone induced limited gene expression changes in sugar beet, as a biotrophic asymptomatic parasite. Most differentially expressed plant genes were down-regulated and included resistance gene analogs and cell wall peroxidases. Several enzymes involved in stress regulation such as the glutathione-S-transferases were significantly induced. With BNYVV, the first stages of P. betae life cycle on sugar beet were accelerated with a faster increase of relative protist DNA level and an earlier appearance of sporangia and sporosori in plants roots. A clear activation of plant defenses and the modulation of genes involved in plant cell wall metabolism were observed. The P. betae transcriptome in the presence of BNYVV revealed induction of genes possibly involved in the switch to the survival stage. The interactions were different depending on the presence – absence of the virus. P. betae alone alleviates plant defense response, playing hide-and-seek with sugar beet and allowing for their mutual development. Conversely, BNYVV manipulates plant defense and promotes the rapid invasion of plant roots by P. betae. This accelerated colonization is accompanied by the development of thick-walled resting spores, supporting the virus survival.
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