Biocontrol of Rhizoctonia solani using volatile organic compounds of solanaceae seed-borne endophytic bacteria

Abstract

Rhizoctonia solani is a broad spectrum fungal pathogen that infects crops in greenhouse and field conditions causing plants damping-off and fruit rot which provoke serious yield losses. This study prospected the use of bacterial volatile organic compounds (VOCs) to control R. solani infection on tomato seedlings and fruit in order to search for an alternative to the use of chemical pesticides. Seed-born bacterial endophytes were isolated from the cultivated Solanum lycopersicum and the wild Solanum linnaeanum species. This study showed a host- and organ-specific colonization of endophytic bacteria at early seedling stage with most of them colonizes the cotyledons in comparison to stems and roots. Overall, 51 % and 11 % of isolated endophytic bacteria produce antifungal VOCs against R. solani at 7 d and 14 d of dual culture, respectively. The majority (about 78 %) of the antagonistic bacterial endophytes showed promoting activity on tomato seedling growth. For the bioprotection tests the strains TRC7 and TRC10 of Bacillus subtilis and TRT11 of B. megateriumwere selected as the most antagonistic and PGP endophytic bacteria and a non-antagonistic strain SMLR7 of Paenibacillus sp., with this later strain reported for the first time colonizing internal seed tissues of S. linnaeanum. The VOCs of the strain TRC7 showed the best pattern of decrease of R. solani rotting on tomato fruit, and increase the hypocotyl length, the radicle length, the fresh weight, and the vigor of tomato seedlings. The identification of the VOCs produced by the antagonistic Bacillus strains showed a core set of four compounds i.e. 2-Heptanone; Pyrazine, 2,5-dimethyl-; Naphthalene; and Benzenamine, N-ethyl- which was the most abundant. All the four VOCs showed antifungal activity against R. solani in vitro growth, and to our knowledge this activity is reported for the first time for Benzenamine, N-ethyl- and 2-Heptanone. The Benzenamine, N-ethyl- showed the best antifungal activity with an IC50 about 0.09 mL L−1 headspace and proved to be effective in reducing R. solani rotting on tomato fruit at the same concentration. So, this work provides evidence about VOCs-mediated biocontrol ability of Bacillus strains to reduce R. solani seedling damping-off and fruit rot of tomato making them valuable agents for pre- and postharvest control of this disease.