With the leadership of researchers from the Agricultural Institute of the ELKH Centre for Agricultural Research (ATK), resistance mechanisms against potato wilt caused by Ralstonia solanacearum have been discovered. It has been determined that in potato cultivars resistant to the bacteria, changes in the levels of certain stress hormones, along with intensified cell wall thickening, production of antimicrobial substances, and reduced activity of certain susceptibility genes collectively lead to the development of resistance. The study presenting the results was published in the international scientific journal Frontiers in Plant Science.
Figure: Symptoms of Calalo Gaspar, Cruza, and Désirée potato cultivars 21 days following infection caused by Ralstonia solanacearum bacteria.
Potatoes are an important cultivated crop in Hungary, but they have been significantly threatened by the tropical-origin Ralstonia solanacearum bacteria, which has emerged within the country in recent decades and causes rot of the tubers and wilting of the plants. Moreover, there is no known effective chemical control against this quarantine pathogen. The existing resistance mechanisms of potatoes against Ralstonia were uncovered through the examination of the expression of each potato gene (transcriptome sequencing), analysis of secondary metabolites produced (UHPLC-MS/MS metabolomics analysis), and the use of modern microscopic techniques (confocal microscope). By testing various cultivars from all over the world, including the susceptible Désirée, two resistant genotypes, Cruza and Calalo Gaspar, were identified and analyzed for their ability to withstand the bacteria. As a result of the experiments, it was determined that the levels of stress hormones, such as abscisic acid, jasmonic acid, and salicylic acid, increased even in the susceptible variety upon infection. However, these hormonal pathways alone were unable to protect the plant from bacterial wilt. The resistant cultivars stood out with greater lignification (cell wall thickening) in the central part of the root (xylem) even without infection. In response to infection, the Cruza cultivar exhibited even more intense cell wall thickening, while the Calalo Gaspar cultivar relied more on the production of antimicrobial substances for defense. Nevertheless, infection led to a decrease in the activity of several sensitivity genes (e.g., WRKY22, 24), which are mentioned in the scientific literature, in both resistant varieties. These sensitivity genes are plant genes, for example, negative immune regulators, interaction partners of pathogenic virulence factors. The proteins they produce can be exploited by the bacteria for their own purposes during infection. In valuable cultivars, it would be worthwhile to induce mutations in these genes in the future, thus enhancing their resistance against bacterial wilt.