Resistance of grapevine and potato against phytoplasmas

The bacterium Candidatus Phytoplasma solani is responsible for a widespread and problematic grapevine disease named Bois Noir. The very same phytopathogenic phytoplasma also infects plants from the nightshade family, including tomato and especially potato causing there stolbur disease. Evidence for resistance against Ca. Phytoplasma solani has not been reported neither in grapevine nor in potato, but differences in susceptibility between cultivars have been observed on the basis of disease incidence, symptom severity, as well as plants ability to recover. As there is no highly effective treatment against phytoplasma infection in grapevine or potato available at the moment and current strategies are relying on pesticide use against transmitting vectors which are active for several weeks, obtaining tolerant cultivars is crucial for future sustainable production and reduction of pesticide use. Loss of function of a plant susceptibility gene involved in compatible interaction that is required by the pathogen for the infection can limit the ability of the pathogen to cause disease. Previous transcriptome analysis in phytoplasma infected grapevine suggests the candidate S gene DMR6 as a promising target for mutagenesis with a good perspective that its deactivation will increase the resistance to phytoplasma and possibly other pathogens. The gene is responsible for deactivation of the plant hormone salicylic acid, which is a crucial component of plant defence against biotrophic pathogens. In the project potato and grapevine lines defective in DMR6 function and other S genes with potentially related functions will be evaluated for their resistanceolerance to Ca. Phytoplasma solani after graft and insect infection. Disease development will be monitored phenotypically and by evaluating phytoplasma titer to obtain knowledge on the role of DMR6 in plant defense against phytoplasma disease. RNA sequencing will be performed in these lines and controls with and without Ca. Phytoplasma solani to analyse the overall effect of DMR6 function on (defense) gene expression. Expression will be verified by quantitative RT- PCR in time series experiments. The experiments will lead to knowledge on the role of the DMR6 S gene family for phytoplasma infection and disease development. Moreover, expression analysis will reveal the degree of pleiotropic effects on gene expression and the effects phytoplasma infection has on this expression pattern. Altogether, this can open up possibilities for better understanding of plant defense and lead to breeding programs and techniques to obtain improved potato and grapevine cultivars.

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