Biological Control Activities of Rice-Associated Bacillus sp. Strains against Sheath Blight and Bacterial Panicle Blight of Rice

Abstract

Potential biological control agents for two major rice diseases, sheath blight and bacterial panicle blight, were isolated from rice plants in this study. Rice-associated bacteria (RABs) isolated from rice plants grown in the field were tested for their antagonistic activities against the rice pathogens, Rhizoctonia solani and Burkholderia glumae, which cause sheath blight and bacterial panicle blight, respectively. Twenty-nine RABs were initially screened based on their antagonistic activities against both R. solani and B. glumae. In follow-up retests, 26 RABs of the 29 RABs were confirmed to have antimicrobial activities, but the rest three RABs did not reproduce any observable antagonistic activity against R. solani or B. glumae. According to16S rDNA sequence identity, 12 of the 26 antagonistic RABs were closest to Bacillus amyloliquefaciens, while seven RABs were to B. methylotrophicus and B, subtilis, respectively. The 16S rDNA sequences of the three non-antagonistic RABs were closest to Lysinibacillus sphaericus (RAB1 and RAB12) and Lysinibacillus macroides (RAB5). The five selected RABs showing highest antimicrobial activities (RAB6, RAB9, RAB16, RAB17S, and RAB18) were closest to B. amyloliquefaciens in DNA sequence of 16S rDNA and gyrB, but to B. subtilis in that of recA. These RABs were observed to inhibit the sclerotial germination of R. solani on potato dextrose agar and the lesion development on detached rice leaves by artificial inoculation of R. solani. These antagonistic RABs also significantly suppressed the disease development of sheath blight and bacterial panicle blight in a field condition, suggesting that they can be potential biological control agents for these rice diseases. However, these antagonistic RABs showed diminished disease suppression activities in the repeated field trial conducted in the following year probably due to their reduced antagonistic activities to the pathogens during the long-term storage in -70C, suggesting that development of proper storage methods to maintain antagonistic activity is as crucial as identification of new biological control agents.

Phyllospheric Microbiomes: Diversity, Ecological Significance, and Biotechnological Applications

“…Sartori et al (2015) studied the biocontrol potential of phyllosphere microorganisms from maize against Exserohi lumturcicum, the causal agent of leaf blight. Shrestha et al (2016) investigated the prospects of biological control of rice-associated Bacillus against sheath blight and panicle blight of rice caused by Rhizoctonia solani and Burkholderia glumae, respectively. A variety of Bacillus isolates were observed to inhibit the sclerotial germination of the fungus, which could be attributed to the various antimicrobial secondary metabolites produced by the bacteria.…”

Molecular identification of bacteria associated with the phyllosphere of rice plants (Oryza sativa L), through microbial culture techniques

“…Si consideramos que la ausencia de bacteria patógena Burkholderia glumae, se debería a la menor producción de toxoflavin, que es dependiente del sistema de "quorum sensing" (Chen et al 2012, Goo et al 2010, Karki 2010y Devescovi et al 2007) y que algunas bacterias tendrían un potencial como agentes de control bio lógico (Shrestha et al 2016); diríamos que los resultados, sobre la no presencia de Burkholderia glumae, pero sí de otras espe cies de este mismo género, se explican con lo expresado anteriormente.…”

Sustainable Strategies for Managing Bacterial Panicle Blight in Rice

“…Miyagawa and Takaya [96] found that an avirulent strain of B. gladioli when applied onto rice panicles was very effective to reduce BPB severity. In the USA, five Bacillus amyloliquefaciens strains were found to be antagonistic against B. glumae in vitro and reduce BPB severity when applied at the heading stage in the field trials conducted in Louisiana [97]. When applied at the flowering stage, two strains of Bacillus sp., with antibacterial activities toward B. glumae, were demonstrated to reduce BPB severity by as much as 50% and increase grain yield by more than 11% in the field trials conducted in Texas [87,88].…”