Effect of anti-fungal compound phytosphingosine in wheat root exudates on the rhizosphere soil microbial community of watermelon

Abstract

The relationship between wheat root exudates and watermelon rhizosphere microbial communities in wheat/watermelon cropping system is well documented now, however, less is known about the activity of allelochemicals in wheat root exudates against watermelon Fusarium oxysporum f. sp. niveum (FON), and how it may influence belowground plant-microbe interactions for disease control. TLC board and UPLC-Q-TOF-MS techniques were used to isolate and analyze the composition of wheat root exudates, and responses of watermelon rhizosphere community against phytosphingosine were analyzed by high-throughput sequencing and quantitative PCR (qPCR). Total of 15 inhibitory compounds were identified in wheat root exudates and most of them were long chain alcohols. Due to highest mass spectral fragment ion matching with already known compounds, we selected phytosphingosine as a model component to study the influence of allelochemical compounds of wheat root exudates on FON and overall rhizosphere microbial community composition of watermelon. Treatment with phytosphingosine increased the diversity of total fungi and bacteria, and altered the compositions of their communities particularly at lower concentration. The abundances and relative abundances of certain potentially plant beneficial bacteria and pathogen-antagonistic fungi were stimulated at lower concentration, while potentially pathogenic fungi including FON were inhibited at different degree. Phytosphingosine inhibited the FON directly, regulated the microbial community structure in watermelon rhizosphere and formed an environment not conducive to pathogen invasion, eventually alleviating the incidence of watermelon Fusarium wilt in wheat/watermelon companion cropping system.