Pseudomonas fluorescens SP007s enhances defense responses against the soybean bacterial pustule caused by Xanthomonas axonopodis pv. glycines

Abstract

A bacterial pustule caused by Xanthomonas axonopodis pv. glycines (Xag) is one of the main diseases of soybeans in Thailand. Beneficial microbes crucial to sustainable plant production were examined in this study. Soybean plants were sprayed with Pseudomonas fluorescens SP007s strain three times before Xag infection. The results showed a significant reduction in bacterial pustule disease severity by up to 85%, increased leaf accumulation of salicylic acid with 134% during the infection process of Xag. Furthermore, the Xag population size in soybean leaves was reduced by priming with SP007s. The mechanism of SP007s in the chemical structure of mesophyll was characterized by using the synchrotron radiation-based Fourier transform infrared (SR-FTIR) analysis. The SR-FTIR spectral changes from the mesophyll showed higher integral area groups of polysaccharides (peak of 900–1,200 cm−1). These biochemical changes were involved with the primed resistance of the soybean plants against the bacterial pustule disease as well as the polysaccharide signals that were linked to hypersensitive responses leading to a rapid death of plant cells to effectively restrict the growth of pathogens at the infected site. Therefore, we consider that SP007s can be a promising biocontrol agent by activating immunity of soybean plants.