Lipid profiling of the soybean pathogen Phytophthora sojae using Fatty Acid Methyl Esters (FAMEs)

Phytophthora sojae is a destructive soilborne pathogen of soybean, but currently there is no rapid or commercially available testing for its infestation level in soil. For growers, such information would greatly improve their ability to make management decisions to minimize disease damage to soybean crops. Fatty acid profiling of P. sojae holds potential for determining the prevalence of this pathogen in soil. In this study, the Fatty Acid Methyl Ester (FAME) profile of P. sojae was determined in pure culture, and the profile was subsequently evaluated for its potential use in detecting the pathogen in soil. The predominant fatty acids in the FAME profile of P. sojae are the unsaturated 18C fatty acids (18:1ω9 and 18:2ω6) followed by the saturated and unsaturated 16C fatty acids (16:0 and 16:1ω7). FAME analysis of P. sojae zoospores showed two additional long-chain saturated fatty acids (20:0 and 22:0) that were not detected in the mycelium of this organism. Addition of a known number of zoospores of P. sojae to soil demonstrated that fatty acids such as 18:1ω9, 18:2ω6, 20:1ω9, 20:4ω6, and 22:1ω9 could be detected and quantified against the background levels of fatty acids present in soil. These results show the potential for using selected FAMEs of P. sojae as a marker for detecting this pathogen in soybean fields.

► Fatty acids 14:0, 16:0, 16:1ω7, 18:1ω9, 18:2ω6, 20:4ω6c always detected in P. sojae.
► Fatty acids 18:1ω9 and 18:2ω6 accounted about 55 % of the total fatty acids.
► Fatty acids 20:0 and 22:0 detected in zoospores were not detected in mycelium.
► Unique zoospore fatty acids markers 18:1ω9, 18:2ω6, 20:1ω9, 20:4ω6, and 22:1ω9.
► Selected FAMEs can be used as a marker to detect P. sojae in soybean fields.