Potential of the coffee endophytic Bacillus cereus sensu lato strain CCBLR15 to control the plant-parasitic nematode Radopholus duriophilus

ABSTRACT

Bacillus cereus sensu lato strain CCBLR15 is highly efficient in inducing in vitro the mortality of coffee-parasitic nematodes, including Pratylenchus coffeae and Radopholus duriophilus. In the present study, this strain was further characterised to investigate (1) its taxonomic position, (2) the secreted/non-secreted nature of its nematicidal compounds, and (3) its in planta biocontrol capacity towards R. duriophilus. Firstly, analysis of 16S rRNA gene sequences and motility test indicated that CCBLR15 was closely related to B. cereus sensu stricto. Secondly, nematodes separate expositions in vitro to CCBLR15 culture filtrate and cell lysate revealed that nematicidal activity was attributed to compounds released after bacterial cell lysis. Thirdly, CCBLR15 nematode biocontrol capacity was studied using three Coffea arabica cultivars, either seed- or cutting-propagated. Plants were therefore characterised by different developmental stages, referred to as ‘early' and ‘advanced', with respectively 2-3 and 6-8 leaf pairs. Additionally, plants were grown in unsterilised soil, with a one-month delay between inoculations of bacteria and nematodes to assess the persistence of the nematicidal effects. The presence of R. duriophilus in roots decreased plant growth only in one cultivar whose plants were inoculated at the ‘early' stage. Nonetheless, CCBLR15 pre-inoculation significantly reduced the number of nematodes in roots of all cultivars and inhibited the negative effects of nematodes in ‘early’-inoculated plants. These results demonstrate the capacity of CCBLR15 to control R. duriophilus and constitute an important step before studying the persistence of its biocontrol effects on a longer period or after plants establishment in the field.

KEYWORDS:

• Bacillus cereus sensu lato
• biocontrol
• Coffea arabica
• coffee
• endophyte
• nematodes

Acknowledgements

We are thankful to the Northern Mountainous Agriculture and Forestry Science Institute (NOMAFSI) for having provided the Tha1 cultivar plants. We are grateful to the BREEDCAFS H2020 European project (www.breedcafs.eu/) for the cultivars Centroamericano and Marsellesa plants. Acknowledgement to the Agricultural Genetic Institute (AGI) for the access to the greenhouse and laboratory. We thank IRD for the funding and we thankfully acknowledge colleagues from IRD, CIRAD, and AGI for their critical editing of this manuscript.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

This work was supported by the funding of the French Institute for the Research and Development (IRD) and the Laboratory of Mediterranean and Tropical Symbioses research unit (LSTM) in the frame of the France-Vietnam International Joint Laboratory (Rice, Interactions & Coffee in Environment-phase 2, RICE-2). This research was partially funded by the BREEDCAFS project, which was supported by the EUROPEAN COMMISSION under the Horizon 2020 - Research and Innovation Programme, H2020-SFS-2016-2, Grant Agreement Number: 727934.