Studies towards late blight control in potato

Sammanfattning: Abstract The oomycete Phytophthora infestans, which causes the devastating late blight disease of potato, is notorious for developing resistance to conventional control strategies (fungicide application and resistance breeding by introgression of R gene). To increase our tool box of disease management strategies available to combat P. infestans, there is a need to explore several new approaches that can lead to more durable solutions to control late blight disease. Using the potato-P. infestans pathosystem, different approaches were used in this thesis with an aim to enhance potato defence and find new resistance sources to P. infestans. In the first approach, exogenous application of a new natural agent, sugar beet extract (SBE), resulted in significant reduction of the size of the infection lesions. The pattern was similar to that seen with application of a known defence-inducing compound, β- aminobutyric acid (BABA). SBE triggered pathogenesis-related protein production with no toxic effect on pathogen growth from SBE was noted, which suggests that the protection conferred by SBE is via induced resistance. BABA is a non-protein amino acid that was shown to induce resistance in different plant species and against various pathogens. However, its mechanism of induced resistance (IR) activation in potato to P.infestans is unclear. Thus, in the second approach, a proteomic and transcriptomic study was conducted in an attempt to unravel the mechanism of BABA-IR in potato. It became clear from our study that BABA results in direct activation of several hormonerelated pathways and defence-related proteins. In the third approach, a constitutively activated defence was discovered in one Phytophthora-resistant potato clone (out of two investigated), which could be an interesting starting material in resistance breeding. In the fourth approach, engineering potato plants by in planta expression of pathogen-associated molecular patterns (Pep13 and flg22) resulted in significant reduction of late blight severity, which could be a suitable strategy to alleviate the severity of plant diseases. An integrated pest management approach, including reduction of the use of the fungicides, is one of the recommendations of the recent EU directive. Thus, it is anticipated that combining induced resistance principle and/or a properly designed transgenic approach with conventional control strategies can reduce fungicide inputs and provide a more efficient and sustainable solution for late blight problem.