Taxonomy Identification and Phytotoxic Activities of Pectolytic Bacteria Isolated from Diseased Plants of Phalaenopsis Blume (Orchidaceae)

Orchid plants, due to their high aesthetic qualities of large inflorescences, long flowering period, and ease of care, have high commercial potential; however, when grown industrially in factories, they are susceptible to infectious diseases. In this study, we isolated from Phalaenopsis spp. plants epiphytic, rhizospheric, and endophytic bacteria associated with soft rot symptoms. Twenty-nine isolates exhibiting pectolytic activity were identified as strains of the genera Bacillus, Klebsiella, Microbacterium, Paenibacillus, Paracidovorax, Pseudomonas, and Psychrobacillus based on 16S rRNA analysis. These isolates were tested for their ability to produce cellulase, amylase, sucrase, proteinase, and lipase; to form biofilms; and to exhibit motility (swimming and swarming). Potato microplants under in vitro conditions were used as a model object for initial screening of the strains’ potential phytotoxicity. Most strains were shown to inhibit plant growth, particularly root development. Injection of suspensions of these strains into orchid leaves caused symptoms of soft rot. Thus, we isolated Gram-positive bacteria for the first time from orchid tissues with soft rot symptoms and demonstrated an association of these strains with plant tissue maceration in potato and orchids. Gram-positive bacteria with pectolytic activity are not typical pathogens of orchid soft rot and may require changes in approaches to the monitoring of phytopathogens for this group of plants.