Identification and Characterization of Bacillus tequilensis GYUN-300: An Antagonistic Bacterium Against Red Pepper Anthracnose Caused by Colletotrichum acutatum in Korea.

Jungyeon Kim,Heung Tae Kim,Hyeok-Tae Kwon,Yongho Jeon,Younmi Lee,Kotnala Balaraju

doi:10.3389/fmicb.2022.826827

Jungyeon Kim, Heung Tae Kim + Show 4 more

Open Access

https://doi.org/10.3389/fmicb.2022.826827

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Abstract

Anthracnose is a fungal disease caused by Colletotrichum species and has detrimental effects on many crops, including red pepper. This study used Bacillus tequilensis GYUN-300 (GYUN-300), which exhibit antagonistic activity against the fungal pathogen, Colletotrichum acutatum. This pathogen causes anthracnose that manifests primarily as a fruit rot in red pepper. There have been little efforts to identify antagonistic bacteria from mushrooms; this strain of bacteria was identified as B. tequilensis using BIOLOG and 16S rDNA sequencing analysis. The genetic mechanism underpinning the biocontrol traits of GYUN-300 was characterized using the complete genome sequence of GYUN-300, which was closely compared to related strains. GYUN-300 inhibited mycelial growth and spore germination of C. acutatum under in vitro conditions. Important antagonistic traits, such as siderophore production, solubilization of insoluble phosphate, and production of lytic enzymes (cellulase, protease, and amylase), were observed in GYUN-300, These trains promoted growth in terms of seed germination and vigorous seedling growth compared to the non-treated control. When red pepper fruits were treated with GYUN-300, the preventive and curative effects were 66.6 and 38.3% effective, respectively, in wounded red pepper fruits; there was no difference between the preventive and curative effects in non-wounded red pepper fruits. Furthermore, GYUN-300 was resistant to several commercial fungicides, indicating that GYUN-300 bacterial cells may also be used synergistically with chemical fungicides to increase biocontrol efficiency. Based on in vitro results, GYUN-300 played a role to control anthracnose disease effectively in field conditions when compared to other treatments and non-treated controls. The results from this study provide a better understanding of the GYUN-300 strain as an effective biocontrol agent against red pepper anthracnose; this form of biocontrol provides an environment-friendly alternative to chemical fungicides.

Highlights

Red pepper (Capsicum annuum L.) is a vegetable crop belonging to the Solanaceae family, with the cultivation area of 33,373 hectares
The dual culture plate assay on the potato dextrose agar (PDA) medium exhibited greater inhibition of mycelial growth of C. acutatum KACC42403 on PDA plates 5 days after incubation at 25◦C, while growth inhibition was not observed in the non-treated control (Figure 2)
When conidial spores of C. acutatum KACC42403 were treated with GYUN-300 bacterial cell suspensions (106 colony-forming units (CFU)/mL) or their culture filtrate (CF) under in vitro conditions, there were different levels of damages in the conidia germination and germ tube lengths; these were compared to the non-treated control

Summary

Introduction

Red pepper (Capsicum annuum L.) is a vegetable crop belonging to the Solanaceae family, with the cultivation area of 33,373 hectares. A large quantity of chemical pesticides is utilized annually to control various bacterial, fungal, and viral diseases on red pepper crops in Korea (Hong et al, 2015). Among all pathogens that cause diseases in red peppers, anthracnose caused by a wide range of Colletotrichum species results in serious losses of fruits during the pre- and post-harvest stages (Ali et al, 2016), while occasionally damaging the stem and foliage (Mishra et al, 2018; Mongkolporn and Taylor, 2018). The fungal species of Colletotrichum cause anthracnose in several plants, including red peppers (Siddiqui and Ali, 2014). Anthracnose in red pepper is associated with several Colletotrichum species, including C. acutatum (Harp et al, 2014), this may infect other fruit and vegetable crops (Han et al, 2015). Red pepper anthracnose is typically characterized by dark brown to black, circular watersoaked spots with concentric rings of black acervuli developing beneath the skin of the fruit (Parisi et al, 2020); the spots are often numerous and coalesce, causing softening and fruit rot (Montri et al, 2009)

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