Abstract
In the plant rhizosphere and endosphere, some fungal and bacterial species regularly co-exist, however, our knowledge about their co-existence patterns is quite limited, especially during invasion by bacterial wilt pathogens. In this study, the fungal communities from soil to endophytic compartments were surveyed during an outbreak of tobacco wilt disease caused by Ralstonia solanacearum. It was found that the stem endophytic fungal community was significantly altered by pathogen invasion in terms of community diversity, structure, and composition. The associations among fungal species in the rhizosphere and endosphere infected by R. solanacearum showed more complex network structures than those of healthy plants. By integrating the bacterial dataset, associations between fungi and bacteria were inferred by Inter-Domain Ecological Network (IDEN) approach. It also revealed that infected samples, including both the rhizosphere and endosphere, had more complex interdomain networks than the corresponding healthy samples. Additionally, the bacterial wilt pathogenic Ralstonia members were identified as the keystone genus within the IDENs of both root and stem endophytic compartments. Ralstonia members was negatively correlated with the fungal genera Phoma, Gibberella, and Alternaria in infected roots, as well as Phoma, Gibberella, and Diaporthe in infected stems. This suggested that those endophytic fungi may play an important role in resisting the invasion of R. solanacearum.
Highlights
Ralstonia solanacearum, the causative agent of soil-borne bacterial wilt disease in plants, is often found in agricultural land used for tobacco cultivation
The purposes of the current study are to: (i) Illuminate the characteristics of fungal communities in the bulk and rhizosphere soils and the root and stem endophytic compartments of healthy tobacco plants and those infected by R. solanacearum; (ii) Reveal the associations among species of fungal communities from various zones of the plant-soil microecosystem via molecular ecological network analysis; (iii) Explore the associations between fungi and bacteria through interdomain ecological network (IDEN) analysis; (iv) Study the associations between pathogenic Ralstonia members and fungi through sub-network analysis, and to explore fungal biocontrol resources that may antagonize the bacterial wilt pathogen
The results showed that the fungal genera Phoma, Gibberella, Alternaria, Haematonectria, Cryptococcus, Podospora, Spodiobolus, Malassezia, Aleuria, Dioszgia, Davidiealla, and unclassified genera were negatively correlated with the pathogenic Ralstonia members in the root endophytic communities (Figure 6), and the fungal genera Phoma, Gibberella, Diaporthe, Didymella, and unclassified genera were negatively correlated with Ralstonia members in the stem endophytic communities (Figure 6)
Summary
The causative agent of soil-borne bacterial wilt disease in plants, is often found in agricultural land used for tobacco cultivation. Plant microbial communities live and colonize several zones including the bulk soil, rhizosphere soil, phyllosphere, and endosphere (Bulgarelli et al, 2013; Kumar et al, 2017) They play a vital role in the acquisition of nutrients by plants, mutual defense, and co-evolution (Martin et al, 2017; Fitzpatrick et al, 2018). The purposes of the current study are to: (i) Illuminate the characteristics of fungal communities in the bulk and rhizosphere soils and the root and stem endophytic compartments of healthy tobacco plants and those infected by R. solanacearum; (ii) Reveal the associations among species of fungal communities from various zones of the plant-soil microecosystem via molecular ecological network analysis; (iii) Explore the associations between fungi and bacteria through interdomain ecological network (IDEN) analysis; (iv) Study the associations between pathogenic Ralstonia members and fungi through sub-network analysis, and to explore fungal biocontrol resources that may antagonize the bacterial wilt pathogen. We will provide a new strategy and theoretical support for enriching the study of tobacco endophytic fungal resources and for exploring the antagonistic fungal resources targeting R. solanacearum
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