Macrophomina phaseolina and Rhizoctonia solani are considered two major soil-borne pathogens of Phaseolus vulgaris in Cuba. Their management is difficult, not only due to their intrinsic biology as soil-borne pathogens, but also because the lack of active ingredients available against these pathogens. Actinobacteria, a heterogeneous bacterial group traditionally known as actinomycetes have been reported as promising biological control agents (BCAs) in crop protection. Thus, the main objective of this study was to evaluate the effectiveness of 60 actinobacterial strains as BCAs against M. phaseolina and R. solani in vitro by dual culture assays. The most effective strains were characterized according to their cellulolytic, chitinolytic and proteolytic extracellular enzymatic activity, as well as by their morphological and biochemical characters in vitro. Forty and 25 out of the 60 actinobacteria strains inhibited the mycelial growth of M. phaseolina and R. solani, respectively, and 18 of them showed a common effect against both pathogens. Significant differences were observed on their enzymatic and biochemical activity. The morphological and biochemical characters allow us to identify all our strains as species belonging to the genus Streptomyces. Streptomyces strains CBQ-EA-2 and CBQ-B-8 showed the highest effectiveness in vitro. Finally, the effect of seed treatments by both strains was also evaluated against M. phaseolina and R. solani infections in P. vulgaris cv. Quivicán seedlings. Treatments combining the two Streptomyces strains (CBQ-EA-2 + CBQ-B-8) were able to reduce significantly the disease severity for both pathogen infections in comparison with the non-treated and inoculated control. Moreover, they showed similar effect than that observed for Trichoderma harzianum A-34 and with Celest® Top 312 FS (Syngenta®; Basilea, Switzerland) treatments, which were included for comparative purposes.
Dada la importancia que tendría el uso de bacterias endófitas para el control de las enfermedades del cacao, el objetivo de este estudio fue construir el árbol filogenético y caracterizar las bacterias endofíticas formadoras de endosporas en función de la altitud, la edad y el tejido de la planta de cacao en una zona productora de la provincia de Esmeraldas en Ecuador. El aislamiento de las bacterias se realizó a partir de secciones de tejidos de mazorcas y pedicelos de la flor en cultivares de cacao Criollo tipo Nacional. Se obtuvieron 45 aislados de bacterias endófitas formadoras de endosporas, asociados principalmente con tejidos del endocarpio. El árbol filogenético reveló que todas las bacterias pertenecen al género Bacillus. No se encontró relación entre el número de aislados bacterianos con la edad de la planta, aunque hubo una ligera tendencia a la disminución de los aislados hacia los sitios de mayor altitud.
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