Bacterial Tomato Pathogen Ralstonia solanacearum Invasion Modulates Rhizosphere Compounds and Facilitates the Cascade Effect of Fungal Pathogen Fusarium solani.

Lv Su,Eiko E Kuramae,Duoqian Nie,Qirong Shen,Lifan Zhang,Biao Shen

doi:10.3390/microorganisms8060806

Abstract

Soil-borne pathogen invasions can significantly change the microbial communities of the host rhizosphere. However, whether bacterial Ralstonia solanacearum pathogen invasion influences the abundance of fungal pathogens remains unclear. In this study, we combined high-throughput sequencing, qPCR, liquid chromatography and soil culture experiments to analyze the rhizosphere fungal composition, co-occurrence of fungal communities, copy numbers of functional genes, contents of phenolic acids and their associations in healthy and bacterial wilt-diseased tomato plants. We found that R. solanacearum invasion increased the abundance of the soil-borne pathogen Fusarium solani. The concentrations of three phenolic acids in the rhizosphere soil of bacterial wilt-diseased tomato plants were significantly higher than those in the rhizosphere soil of healthy tomato plants. In addition, the increased concentrations of phenolic acids significantly stimulated F. solani growth in the soil. Furthermore, a simple fungal network with fewer links, nodes and hubs (highly connected nodes) was found in the diseased tomato plant rhizosphere. These results indicate that once the symptom of bacterial wilt disease is observed in tomato, the roots of the wilt-diseased tomato plants need to be removed in a timely manner to prevent the enrichment of other fungal soil-borne pathogens. These findings provide some ecological clues for the mixed co-occurrence of bacterial wilt disease and other fungal soil-borne diseases.

Highlights

Bacterial wilt caused by Ralstonia solanacearum is a destructive and widespread soil-borne disease [1,2], and it is not effectively controlled in the field [3]
Whether R. solanacearum invasion can affect fungal communities, whether changes in fungal pathogens occur in the rhizosphere of tomato plants, remains unknown
Our aim is to determine whether the fungal community composition, the fungal pathogens, and the fungal networks are affected by R. solanacearum invasion in the rhizosphere of tomato plants

Summary

Introduction

Bacterial wilt caused by Ralstonia solanacearum is a destructive and widespread soil-borne disease [1,2], and it is not effectively controlled in the field [3]. It is known that R. solanacearum invasion significantly affects the diversity and composition of the bacterial community in the tomato rhizosphere [4,5]. Foot rot of tomato caused by the fungal pathogen Fusarium solani is another soil-borne disease that limits tomato production [6]. F. solani can infect tomato roots and young foliage. A dark brown lesion of about 1 inch long can be visible on the tap root or a main lateral root, and the infected foliage shows interveinal chlorosis and necrotic spotting [7]. Whether R. solanacearum invasion can affect fungal communities, whether changes in fungal pathogens occur in the rhizosphere of tomato plants, remains unknown

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