The use of mycorrhizal fungi as a strategy to increase resistance against grapevine diseases: study of the effect of mycorrhizal symbiosis on Plasmopara viticola ability to express pathogenic effectors
Tese de mestrado, Microbiologia Aplicada, Universidade de Lisboa, Faculdade de Ciências, 2020Grapevine is one of the most important fruit crops worldwide. In 2019, over 7.4 million hectares of the world cultivated area were dedicated to viticulture, resulting in the production of 77.8 million tonnes of grapes (International Organisation of Vine and Wine, 2020 report). However, the cultivated species Vitis vinifera L., widely used for berry and wine production, is highly susceptible to the pathogenic oomycete Plasmopara viticola (Berk. & M.A. Curtis) Berl. & De Toni, the causal agent of the grapevine downy mildew disease. This disease is one of the most devastating causing up to 75% of grape loss in one season and important economic losses. Nowadays, the method used to control P. viticola relies on multiple applications of chemical fungicides which have a negative impact on the environment as they accumulate in the soil and water. In Europe alone, 68 thousand tonnes of fungicides were used in 2003, but recently the European Union has established a goal to lower the usage of such chemicals in viticulture. Therefore, there is a need to develop new and more sustainable strategies to control downy mildew disease. The use of beneficial microorganisms with biocontrol capabilities, such as the arbuscular mycorrhizal fungi (AMF), has been pointed out as a viable alternative. With this study we intended to investigate the effect of AMF colonization on the expression of P. viticola effectors during infection of grapevine. Grapevine plants (V. vinifera cv Cabernet Sauvignon) were inoculated with the mycorrhizal fungus Rhizophagus irregularis and root AMF colonization rate and plant growth were assessed. The percentage of root colonization was 10% and mycorrhizal grapevine plants showed a significantly higher shoot biomass compared to non-mycorrhizal plants. Four months post-mycorrhizal inoculation, plants were infected with the pathogen P. viticola. Pathogenicity effectors genes belonging to the RxLR group were analysed and their expression was investigated during the first hours of infection using quantitative real time PCR analysis. Results showed that mycorrhizal inoculation altered the expression of several P. viticola effectors, namely PvRxLR28 and PvRxLR67 that presented an expression decrease in mycorrhizal plants at the two time points post-infection tested, and PvRxLR18 and PvAVH52 that presented an expression increase. These results suggest that the pre-inoculation of grapevine with AMF may interfere with pathogen capabilities to infect the plant by pathogenicity effectors expression modulation. These results further support the hypothesis that AMF can be used to promote more sustainable agriculture, particularly viticulture, practices
