Studies towards late blight control in potato

Detta är en avhandling från Department of Biology, Lund University

Sammanfattning: Popular Abstract in English Plant diseases are directly associated with food security because they result in severe reduction of plant yield and thus they add to the scarcity of foods in the world, which can lead to negative repercussions on humankind. Late blight disease that severely hit Ireland in 1840s, which was caused by Phytophthora infestans and is mentioned in the historical records as the Irish Famine, can be a testimony of the involvement of plant pathogens in human tragedies and shaping the history of humankind. Through constant research and discoveries, it became clear that control of plant diseases could be done by breeding resistant varieties and by using agrochemicals, which led to enhanced plant protection and increased yields. Plant pathogens became increasingly resistant to these conventional control strategies due to their excessive and wide-spread use in different parts of the world. Taking P.infestans as an example, recent research conducted in the areas of genome sequencing, pathogenicity, and genetics revealed tactics used by this this devastating pathogen to defeat resistance conferred by the resistant varieties and fungicides. It is now evident that this pathogen contains several classes of transposons (jumping DNA elements) that can accelerate pathogen evolution and also several types of pathogen proteins (named effectors) that affect the host. Effectors can be viewed as a double-edged sword: they can either result in resistance in plants that can have the required recognition system to recognize these effectors so that the plants can be immunized against these pathogen isolates, or they can result in disease initiation by suppression of the plant recognition system. Because of these issues combined with the hazards that fungicides can have on health and environment, new approaches to control plant diseases are now required. Plants are known to have their own immune system and they induce various defence responses when they encounter different stresses like pathogens. It was found, for example, that synthetic chemicals like analogues of plant hormones or the non essential amino acid β-aminobutyric acid (BABA), when applied to plants can result in enhanced resistance to pathogens because these chemicals, which are called plant defence activators, activated plant defence responses and made the plant on the alert against future plant infection in a more efficient way than the non-treated plants. This is known as induced resistance and it is an interesting area of research with potential application in modern agriculture. However, the prices of these chemicals can be prohibitive for farmers. It stands to reason that natural and cheap agents that can have defence-inducing ability can be an interesting alternative. I have found that sugar beet extract (SBE), extracted through a simple extraction method from a large-scale plant waste product, could induce defence in potato to P. infestans in a similar way in which the synthetic chemical BABA does. The agent reduced the infection lesions on the plants and reduced the total number of 26 infectious propagules (sporangia) in plants, which indicates a good potential for its possible use in organic farming or in general plant disease control strategies. The need to understand the mechanism of plant defence activators is important to study in order to effectively apply these agents in large-scale application in agriculture. BABA is a well-known defence inducing agent, thus its mechanism of induced resistance was studied in potato after BABA treatment to understand why potato plants become more resistant to P. infestans. In order to study the changes after BABA treatment, detailed proteomic and transcriptomic study was conducted for this purpose, which found that direct activation of hormone-related pathways and defence-related proteins was involved in the induced resistance. In another project, it was found that a Phytophthora-resistant potato clone from potato breeding program displayed constitutive activation of plant defences without any pathogen stress, which can be a good basis for future breeding efforts. Resistance can be engineered by genetically modifying plants. During plant-microbe interactions, some molecules are released from pathogens, which are termed pathogen-associated molecular patterns (PAMPs) and which are recognized by specific plant receptors to activate plant defences. I have found that by expressing two PAMPs in potato plants, one from bacteria (flg22) and the other one from Phytophthora spp. (pep13), significant reduction of late blight severity was achieved, which can be an interesting strategy to control late blight disease. Moreover, it is possible to combine the transgenic approach or the induced resistance breeding with the conventional control strategies to provide a more efficient and durable solution for the late blight problem.