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Identification of bacterial endophytes of interest for coffee crop in Vietnam

Duong B., Nguyen H.X., Phan H.V., Colella S., Trinh P.Q., Hoang G.T., Nguyen T.T., Marraccini P., Lebrun M., Duponnois R.. 2021. In : 28th Conference of Association for the Science and Information on Coffee - Books of abstracts. Montpellier : ASIC, p. 89. Conference of Association for the Science and Information on Coffee (ASIC 2021). 28, 2021-06-28/2021-07-01, Montpellier (France).

RATIONALE - This project aimed to identify some plant growth promoting agents, as well as some biocontrol agents of coffee parasitic nematodes and fungal pathogens based on bacterial endophytes naturally associated with coffee roots and seeds in Vietnam. Bacteria were identified and selected with in vitro screenings for some potential plant growth promoting and biocontrol capacities. Subsequently, direct confrontations with the plant parasitic nematodes Radopholus duriophilus and Pratylenchus coffeae, as well as the phytopathogenic fungus Fusarium oxysporum were performed in order to highlight the bacterial endophytes nematicidal and antifungal activities. METHODS - Bacterial endophytes were identified by sequencing of the 16S rRNA coding gene and preliminary screenings for phosphate solubilization, as well as the production of siderophores, hydrogen cyanide, gelatinases, chitinases, lipases and esterases were performed in vitro. Then, 50 bacterial isolates were selected for in vitro direct confrontations with the nematodes and the phytopathogenic fungus. After 48 h, R. duriophilus mortality risk ratios (percentage of mortality in treatment divided by percentage of mortality in control) were calculated. Then, isolates with risk ratios higher than 2 were further characterized with different concentrations in order to calculate lethal doses on R. duriophilus and P. coffeae at 24 h. Finally, dual cultures were used to highlight the antifungal activity of the isolate on F. oxysporum (expressed in percentage of fungal growth inhibition). RESULTS - Fifty isolates were selected after the in vitro preliminary screenings for direct confrontation plant parasitic nematodes and the fungal phytopathogen. Seventeen isolates displayed R. duriophilus mortality risk ratios higher than 2 after 48 h of which 11 were tested at different concentrations at 24 h on both R. duriophilus and P. coffeae. Finally, 17 isolates displayed an antifungal activity on F. oxysporum with a growth inhibition comprised between 8 % and 50 %. The results for all the screenings are presented. CONCLUSIONS & PERSPECTIVES - Several have displayed some nematicidal and/or some antifungal activities. The nematode biocontrol potential of one of the most efficient isolates on the nematode were confirmed in planta. We used the isolate CCBLR15 to control the parasitic nematode R. duriophilus on C. arabica and the result are currently under submission for publication.

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