Phytophthora species are destructive oomycete soilborne plant pathogens with a broad host range. They cause significant economic losses to crops worldwide as well as damage to natural ecosystems.
Spread of Phytophthora mainly occurs through the movement of infested soil, water, and infected plants. Management of Phytophthora species use a combination of common horticultural practices such as burning infected plants, creating buffer zones around infected areas, and spraying the orchards with chemical pesticides such as phosphite. Continuous use of such chemical pesticides has already resulted in resistant variants of the pathogen, rendering the pesticide ineffective in such cases. The complex life cycle of this pathogen makes it very challenging to control Phytophthora outbreaks and protect plants.
To develop environmentally friendly options to protect plants from aggressive Phytophthora, we screened several anti-fungal compounds against the different life stages of a range of Phytophthora species such as P. cinnamomi, that is a major problem for the global avocado industry, and P. agathidicida, the main pathogen responsible for causing the dieback disease to kauri, the native tree of New Zealand that holds great cultural significance to the country.
An antifungal lipopeptide developed in our lab and a natural product extracted from the leaves of horopito, an endemic shrub to New Zealand, were found to have promising activity against different life stages of the Phytophthora they were tested against, including mycelia, zoospores and to some extent oospores. Zoospores are short lived motile spores, that travel through soil and water and infect new hosts, whereas the thick-walled oospores remain dormant in the soil for several years until favourable conditions such as rainfall cause their germination spreading the pathogen to new crops. Effective methods to prevent the germination and motility of zoospores as well as to inactivate the long-surviving oospores are greatly sought after in Phytophthora management.
Further investigations on the potential of the above two promising compounds established that they protect kauri and avocado leaves from Phytophthora infection without causing phytotoxicity. Because of their biodegradability and natural origin, the anti-Phytophthora compounds identified in this research provide a great deal of hope in the development of environmentally friendly methods for Phytophthora control globally.
Gayan H. De Zoysa, Luitgard Schwendenmann, Nick Waipara and Vijayalekshmi Sarojini published this study in Plant Pathology:
TITLE IMAGE: Anti-Phytophthora lipopeptide disrupts the lifecycle: mycelia of Phytophthora multivora (top panel) and oospores of Phytophthora agathidicida (bottom panel) viewed under a scanning electron microscope, show damaged structures after treatment with the anti-Phytophthora lipopeptide identified in this research. All images used with permission of the author.