Molecular aspects of resistance to late blight disease in potato (solanum tuberosum L.)

Diseases caused by micro-organisms are still a major threat to the agro-industry worldwide. Diseases not only have negative effects on crop yields, but also they can affect the quality of crops post-harvest. Genetic engineering is one of several strategies that have been developed to control plant diseases and to enhance plant disease resistance to pathogens. Although some genetic strategies have provided plants with enhanced disease resistance, some pathogens can easily overcome this resistance by rapid evolution resulting in a lack of durability in the field. The oomycete Phytophthora infestans, the causal pathogen of late blight disease of potato, is an example of a crop pathogen that causes a major problem in one of the most important crops worldwide. Many efforts have been made trying to control this pathogen including chemical controls and genetic engineering, but unfortunately it remains a severe problem and the control measures are rarely very successful. Due to the complexity of this pathogen, and to limit the need for chemical control, breeding programmes to incorporate durable forms of genetic resistance are crucially needed. Although, this type of resistance is believed to be effective against all known races of P. infestans and provide in additional some level of general resistance, until now the genetic bases of this type of resistance is still unknown and the molecular mechanisms poorly understood. This project set out to isolate and identify gene sequences that are induced during the compatible interaction between cultured potato plants and P. infestans, specifically those leading to the establishment of durable resistance. It was demonstrated that the potato variety Stirling is capable of developing this type of resistance as judged by the development of resistant shoots during the interaction with Phytophthora. These shoots showed very strong resistance not only to Phytophthora but also to other potato pathogens (R. solani and F. sulphureum) even after two generations of culturing the plants in the absence of the pathogen. The fast production of ROS and the tight deposition of callose surrounding the hypersensitive cells, which deprive the pathogen of nutrients and limit pathogen growth to a small region of the plant, may be important factors in the success of the durable plants in defending themselves against the pathogen attack.