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

Bishnu K Shrestha,Hari Sharan Karki,Jong Hyun Ham,Donald E Groth,Nootjarin Jungkhun,Adam Driks

doi:10.1371/journal.pone.0146764

Bishnu K Shrestha, Hari Sharan Karki + Show 4 more

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https://doi.org/10.1371/journal.pone.0146764

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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.

Highlights

A diverse range of microorganisms dwell in various parts of a plant, causing detrimental, neutral or beneficial effects on plant health [1,2,3]
12 of the 26 antagonistic RAB strains (RABs) were closest to B. amyloliquefaciens, and seven of the remaining 14 RABs were to B. methyllotrophicus and B. subtilis, respectively (Table 1)
Five RABs showing highest antimicrobial activities (RAB6, RAB9, RAB16, RAB17S and RAB18) were effective in suppressing the development of sheath blight and bacterial panicle blight in the field condition if they were sprayed to rice plants prior to pathogen inoculation

Summary

Introduction

A diverse range of microorganisms dwell in various parts of a plant, causing detrimental, neutral or beneficial effects on plant health [1,2,3]. Antagonistic bacteria isolated from plant surface, soil and rhizosphere have been extensively used to control major crop diseases caused by various fungal and bacterial diseases [6, 7]. Those microorganisms can be used alone or in combination with other chemical or biological control agents for various crop diseases [1,2,3, 6, 8, 9] [10, 11]. Sheath blight is one of the most economically important rice diseases worldwide, which is caused by the fungal pathogen Rhizoctonia solani. Various fungicides are being used to control the disease [13,14,15], fungicide application increases the cost of cultivation and the risk of the emergence of fungicide-resistant pathogens [16]

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