The Bacterial Wilt Reservoir Host Solanum dulcamara Shows Resistance to Ralstonia solanacearum Infection.

Pau Sebastià,Anurag Kashyap,Benoit Daubech,Roger De Pedro-Jové,Marc Valls,Núria S Coll

doi:10.3389/fpls.2021.755708

Pau Sebastià, Anurag Kashyap + Show 4 more

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https://doi.org/10.3389/fpls.2021.755708

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Abstract

Ralstonia solanacearum causes bacterial wilt, a devastating plant disease, responsible for serious losses on many crop plants. R. solanacearum phylotype II-B1 strains have caused important outbreaks in temperate regions, where the pathogen has been identified inside asymptomatic bittersweet (Solanum dulcamara) plants near rivers and in potato fields. S. dulcamara is a perennial species described as a reservoir host where R. solanacearum can overwinter, but their interaction remains uncharacterised. In this study, we have systematically analysed R. solanacearum infection in S. dulcamara, dissecting the behaviour of this plant compared with susceptible hosts such as tomato cv. Marmande, for which the interaction is well described. Compared with susceptible tomatoes, S. dulcamara plants (i) show delayed symptomatology and bacterial progression, (ii) restrict bacterial movement inside and between xylem vessels, (iii) limit bacterial root colonisation, and (iv) show constitutively higher lignification in the stem. Taken together, these results demonstrate that S. dulcamara behaves as partially resistant to bacterial wilt, a property that is enhanced at lower temperatures. This study proves that tolerance (i.e., the capacity to reduce the negative effects of infection) is not required for a wild plant to act as a reservoir host. We propose that inherent resistance (impediment to colonisation) and a perennial habit enable bittersweet plants to behave as reservoirs for R. solanacearum.

Highlights

Alternate or reservoir hosts are non-target organisms that can harbour high amounts of pathogens for long periods of time and serve as an inoculum source for further infections on the primary host (Haydon et al, 2002; Morris et al, 2009)
Pseudomonas syringae isolated from wild species was shown to potentially develop into novel crop pathovars in a few evolutionary steps (Monteil et al, 2013; Bartoli et al, 2015), and experimental evolution experiments with Ralstonia solanacearum demonstrated high fitness gains when this pathogen was inoculated on distant hosts (Guidot et al, 2014)
To analyse the symptomatology caused by R. solanacearum in S. dulcamara and compare its behaviour with that of tomato, we inoculated plants in controlled conditions using two different methods

Summary

Introduction

Alternate or reservoir hosts are non-target organisms that can harbour high amounts of pathogens for long periods of time and serve as an inoculum source for further infections on the primary host (Haydon et al, 2002; Morris et al, 2009). In many important crop diseases, non-agricultural reservoirs have been proposed to enhance the adaptive potential of pathogens and influence disease epidemiology (Mueller et al, 2012; Monteil et al, 2013; Thinakaran et al, 2015; McCann, 2020). Pseudomonas syringae isolated from wild species was shown to potentially develop into novel crop pathovars in a few evolutionary steps (Monteil et al, 2013; Bartoli et al, 2015), and experimental evolution experiments with Ralstonia solanacearum demonstrated high fitness gains when this pathogen was inoculated on distant hosts (Guidot et al, 2014). Ralstonia solanacearum is the agent causing the devastating bacterial wilt disease in over 200 plant species, including economically important crops such as potato, tomato, peanut, eggplant, and banana (Hayward, 1994; Mansfield et al, 2012; Coll and Valls, 2013). The disease is endemic in tropical and subtropical areas, but R. solanacearum phylotype II-B1 (formerly race 3 biovar 2) strains are adapted to cooler temperatures and have caused important outbreaks in temperate regions (Elphinstone, 1996; Janse et al, 2004; Champoiseau et al, 2009)

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