Oxylipins as novel sources of soybean (glycine max) tolerance to phytophthora sojae infection

Adigun, Oludoyin Adeseun (2022) Oxylipins as novel sources of soybean (glycine max) tolerance to phytophthora sojae infection. Doctoral (PhD) thesis, Memorial University of Newfoundland.

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Abstract

Soybean (Glycine max) is an important staple crop currently grown worldwide. The annual global losses of the crop due to root and stem rot infection caused by oomycete Phytophthora sojae are currently estimated at approximately $2B USD. The attempt to fight this devastating disease is towards pyramiding tolerant soybean cultivars that could enhance tolerance to Phytophthora sojae infection. The initial point of infection is root and could spread to the stem. Lipids are major structural components of cellular membranes, which serve as a component of defense mechanisms used by plants against pathogen infection. I hypothesized that lipid mediated plant immunity including phyto-oxylipin anabolism culminating in unique histochemical and morphological structures appear to be part of the successful mechanisms used by tolerant soybean cultivar to limit colonization and infection by Phytophthora sojae. These greater alterations are just a component of successful strategy used by tolerant cultivar to mitigate pathogen infection. To investigate these hypotheses, we employed multi-modal lipidomics, scanning electron microscopy and histochemical techniques to determine, (1) how soybean cultivars remodel their lipid metabolism, (2) to better understand the induction and functions of phyto-oxylipins, and (3) to investigate the mechanism of infection in both soybean cultivars in response to Phytophthora sojae infection. Both soybean cultivars demonstrated alterations in lipid metabolism in response to pathogen infection. Relative to non-inoculated controls, induced accumulation of stigmasterol occurred in the susceptible cultivar whereas induced accumulation of phospholipids and glycerolipids was observed in the tolerant cultivar. A comprehensive metabolic map of soybean root and stem lipid metabolism identified unique lipid biomarkers and accumulation of phyto-oxylipins in tolerant cultivar in response to Phytophthora sojae infection. Histochemical results revealed differences in morphological changes in both susceptible and tolerant cultivars and seemed to be associated with the successful mechanisms used by tolerant soybeans to limit pathogen infection. Overall, my thesis findings demonstrate the role of lipid metabolisms and phyto-oxylipin induction in soybeans during pathogen inversion. This information could be useful in pyramiding soybean cultivars with high tolerance to Phytophthora sojae infection and may consequently improve sustainable agriculture.

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