ABSTRACT
Several studies have reported that bacteria produce anti-fungal volatiles. We identified the organic volatile compounds produced by six cacao endophytic bacteria (CEB) strains (Bacillus amyloliquefaciens CFFSUR-B35, Bacillus megaterium CFFSUR-B32, Bacillus muralis CFFSUR-B39, Bacillus pumilus CFFSUR-B34, Bacillus subtilis CFFSUR-B31, and Novosphingobium lindaniclasticum CFFSUR-B36). We evaluated their inhibitory effect on mycelium growth and spore germination of the phytopathogenic fungus Moniliophtora roreri. The volatiles produced by these six CEB, were collected and identified by SPME and GC-MS. Moreover, the inhibitory effect of five synthetic volatile organic compounds, individually and in mixtures (dimethyl disulfide, 2-5 dimethyl pyrazine, α-pinene, 2-heptanone and 2-ethyl hexanol) on M. roreri mycelium growth and spore germination was evaluated. All strains examined produced volatiles in different amounts; 13 to 10 compounds were identified, including sulfide, alcohol benzene derivate, pyrazine, ketone, nitrogen and terpene compounds. The B. subtilis CFFSUR-B31 strain produced the largest number of volatiles, while B. pumilus CFFSUR-B34 produced the fewest and the lowest amounts. The volatile organic compounds produced by B. pumilus CFFSUR-B34, B. muralis CFFSUR-B39 and N. lindaniclasticum CFFSUR-B36 inhibited M. roreri mycelium growth by more than 35%, sporulation by more than 81% and spore germination by more than 74%. However, when synthetic compounds were evaluated individually and in mixtures, 2-ethyl hexanol at 100,000 ppm (20 mg/filter paper disc) inhibited M. roreri mycelium growth by 100%, followed by organic volatile compound mixtures C (dimethyl disulfide, 2,5-dimethyl pyrazine, α-pinene, 2-ethyl-hexanol, 2-Heptanone) and D (only the top four) at 100,000 ppm (4 and 5 mg/filter paper disc) which inhibited spore germination by 97 and 89%, respectively.
Subject(s)
Agaricales , Cacao , Volatile Organic Compounds , Mycelium , Volatile Organic Compounds/pharmacologyABSTRACT
Resumen La orquídea Guarianthe skinneri está incluida en la norma NOM-059-ECOL-2010 de México como una especie amenazada. Con el fin de estudiar las BPCV (bacterias promotoras del crecimiento vegetal) en esta orquídea, se recolectaron 10 raíces de diferentes plantas para aislar bacterias asociadas a las raíces, que se analizaron mediante pruebas in vitro como: producción de AIA, fijación de nitrógeno, interacción con el hongo micorrízico Thanatephorus sp. cepa RG26 y solubilización de fosfato. De los 71 aislados bacterianos se caracterizaron 10 cepas mediante secuenciación con el marcador 16s rADN y se identificaron seis cepas: Sphingomonas sp., Sinorhizobium sp., Bacillus sp., Nocardia cerradoensis, Bacillus megaterium y Burkholderia phytofirmans. Se observó que la bacteria Sinorhizobium sp. produjo mayor cantidad de AIA (69.189 µg/ml) y Bacillus sp. presentó mayor reducción de acetileno (10.251 nmol cultivo/96 h). En las interacciones de las bacterias y el hongo RG26 se presentaron cuatro categorías (sumamente positivo, positivo, antagonismo 50-50 e inhibición). En relación a la solubilización de fosfato, la bacteria Burkholderia phytofirmans presentó mayor IS a las 48 y 96 hr con IS de 3.11 y 3.48, respectivamente. Los resultados indican que Bacillus sp. pudiera tener las mejores características para promover el desarrollo de la orquídea G. skinneri mediante la inoculación de semillas y plántulas.
Abstract The Guarianthe skinneri orchid is included in NOM-059-ECOL-2010, Mexico standard as an endangered species. In order to study PGPR (promoting growth plant rhizobacteria) from this orchid, 10 roots were collected from different plants to isolate bacteria associated with the roots, which were analyzed by in vitro tests such as: production of AIA, nitrogen fixation, interaction with the mycorrhizal fungus Thanatephorus sp. strain RG26 and phosphate solubilization. We obtain 71 bacterial isolates, 10 strains of them were characterized by sequencing with the 16d rDNA marker identifying six bacteria: Sphingomonas sp. Sinorhizobium sp. Bacillus sp. Nocardia cerradoensis, Bacillus megaterium and Burkholderia phytofirmans. We observed that the bacterium Sinorhizobium sp. produced a greater amount of AIA (69.189 μg/ml) and Bacillus sp. performed greater acetylene reduction (10.251 nmol cultivo/96h). In the interactions of the bacteria and the fungus RG26, four categories were presented (extremely positive, positive, antagonism 50-50 and inhibition). In relation to the solubilization of phosphate, Burkholderia phytofirmans presented higher IS after 48 and 96 hr with an IS of 3.11 and 3.48, respectively. The results indicate that Bacillus sp. it could have the best characteristics to promote the development of the G. skinneri orchid by inoculating seeds and seedlings. Rev. Biol. Trop. 66(3): 953-968. Epub 2018 September 01.
