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Doctoral thesis, 2019

The biology and ecology of Phytophthora infestans: the role of cell wall proteins in development, pathogenicity and potato defence activation

Brus-Szkalej, Maja


Phytophthora infestans was one of the first eukaryotic microbes to be implicated as the causal agent of a plant disease. Despite a relentless research effort over the last 150 years, it remains one of the most economically important phytopathogens today. Late blight disease is the most devastating disease of potato and remains a global research focus. Contrary to its initial classification, P. infestans is not a fungus, but an oomycete, part of an entirely separate Kingdom of life and thus, broad spectrum fungicides are usually ineffective. Nonetheless, frequent spraying with synthetic pesticides remains the only efficient means of late blight control. The success of the pathogen stems from its remarkable adaptive ability and the high plasticity of the genome. P. infestans can overcome plant resistance, including resistance introduced through breeding, by rapid evolution of its effectors – molecules secreted to promote infection that can also be recognised by the plant immune system. Thus, non-chemical methods of control are not usually durable. Next-generation pesticides that retain current levels of crop protection whilst lowering their negative impact on the environment are needed. Therefore, the focus of our research was the biology and ecology of the pathogen and our aim was to identify new possible targets for future disease control measures. The cell wall is an essential component of microbial cells and unique components of the P. infestans cell wall are attractive targets for next generation pesticides. We identified two families of cell wall proteins necessary for growth, development and pathogenicity of P. infestans. Moreover, we analysed various commercially available chemicals for their effectiveness as P. infestans cell wall and growth inhibitors. The identification of a putative new P. infestans overwintering strategy in the rhizosphere of wild potatoes generated new hypotheses for the application of chemical fungicides in the future. Finally, in an attempt to increase late blight resistance in potato we expressed a P. infestans cell wall elicitor peptide in planta. This strategy was effective and resistance was increased under controlled conditions, but it was not durable in the field environment, indicating that caution needs to be taken when analysing transgenic plants and highlighting the importance of field trials. Overall, we have shown that several new targets in the oomycete cell wall could be promising leads for the development of nextgeneration pesticides and thus our data make a valuable addition to the understanding of the biology of P. infestans and the control of late blight disease.


Phytophthora infestans; late blight; control strategy; pesticides; oomycete; cell wall

Published in

Acta Universitatis Agriculturae Sueciae
2019, number: 2019:81
ISBN: 978-91-7760-480-8, eISBN: 978-91-7760-481-5
Publisher: Department of Plant Protection Biology, Swedish University of Agricultural Sciences