Biocontrol and plant growth promotion potential of endophytic Bacillus subtilis JY-7-2L on Aconitum carmichaelii Debx.

Abstract

Aconitum carmichaelii Debx. is a famous medicinal plant rich in alkaloids and widely used to treat various human diseases in Asian countries. However, southern blight caused by Sclerotium rolfsii severely hampered the yield of A. carmichaelii. Beneficial microbe-based biological control is becoming a promising alternative and an environmentally friendly approach for the management of plant diseases. In this study, we evaluated the biocontrol potential of an endophytic bacterial strain JY-7-2L, which was isolated from the leaves of A. carmichaelii, against southern blight in vitro and by a series of field experiments. JY-7-2L was identified as Bacillus subtilis based on multi-locus sequence analysis. JY-7-2L showed strong antagonistic activity against S. rolfsii in vitro and on A. carmichaelii root slices by dual-culture assay. Cell-free culture filtrate of JY-7-2L significantly inhibited the hyphal growth, sclerotia formation, and germination of S. rolfsii. In addition, volatile compounds produced by JY-7-2L completely and directly inhibited the growth of S. rolfsii. Furthermore, JY-7-2L was proved to produce hydrolytic enzymes including glucanase, cellulase, protease, indole acetic acid, and siderophore. The presence of bacA, fenA, fenB, fenD, srfAA, and baeA genes by PCR amplification indicated that JY-7-2L was able to produce antifungal lipopeptides and polyketides. Field trials indicated that application of the JY-7-2L fermentation culture significantly reduced southern blight disease severity by up to 30% with a long-acting duration of up to 62 days. Meanwhile, JY-7-2L significantly promoted the fresh and dry weights of the stem, main root, and lateral roots of A. carmichaelii compared to non-inoculation and/or commercial B. subtilis product treatments. Taken together, JY-7-2L can be used as a promising biocontrol agent for the control of southern blight in A. carmichaelii.

Bacillus VOCs in the Context of Biological Control

“…Wu et al [ 99 ] have identified toluene, phenol, and benzothiazole as the main VOCs produced by B. amyloliquefaciens NJZJSB3, which have shown comparable effects to chemical fungicides in terms of reduction of canola stem rot incidence (by 83.3%), caused by Sclerotinia sclerotiorum, in pot experiments. Southern blight of Aconitum carmichaelii Debx., caused by Sclerotium rolfsii , was successfully inhibited (30% with a long-acting duration of up to 62 days) in a field trial by fermentation culture VOCs of B. subtilis JY-7-2L [ 100 ].…”

Culturable bacterial endophytes of Aconitum carmichaelii Debx. were diverse in phylogeny, plant growth promotion, and antifungal potential

“…The dual-culture method was used to test the antifungal activity of endophytic bacteria both in vitro and on A. carmichaelii root slices. In this study, S. rolfsii and F. oxysporum strains were used as targeted pathogens (Li et al, 2020 ; Zou et al, 2023 ). Pathogens were inoculated on potato dextrose agar (PDA) medium and incubated at 25°C for 5 days.…”

Deciphering the mechanisms, hormonal signaling, and potential applications of endophytic microbes to mediate stress tolerance in medicinal plants

“…SMR1 enhanced downy mildew tolerance in Papaver somniferum (L.) via protein modification, differential expression of transcripts related to signal transduction, transcription factors, and SA-dependent defense pathway ( Ray et al., 2021 ). Many researchers showed the ability of both bacterial and fungal endophytes to control diseases and phytopathogens by synthesized volatile and non-volatile compounds, soluble antifungal metabolites and by specific mechanisms including activation of defense enzymes and PR proteins associated with ISR, JA/ET mediated disease resistance, antagonism, antimicrobial, antioxidant, and anti-proliferative properties, production of IAA, siderophores.and β-1,3-glucanase, proteolytic activity, chitinase and cellulose synthesis in diverse medicinal plants including Chloranthus elatior , Taxillus chinensis, Salvia miltiorrhiza, Curcuma longa, Dioscorea bulbifera, Viola odorata, Cremastra appendiculata , Angelica sinensis , Cornus florida, Nicotiana tabacum, Zingiber zerumbet and Piper betle ( Harsha et al., 2023 ; Jiao et al., 2023 ; Manasa et al., 2023 ; Mei et al., 2023 ; Rotich and Mmbaga, 2023 ; Salwan et al., 2023 ; Santra and Banerjee, 2023 ; Sharma et al., 2023 ; Song et al., 2023 ; Thankam and Manuel, 2023 ; Wang et al., 2023 ; Yehia, 2023 ; Zou et al., 2023 ).…”

“…To illustrate, several studies have reported the beneficial effects of microbial endophytes on a wide range of medicinal plants, including Withania somnifera, Artemisia annua, Papaver somniferum, Cymbidium aloifolium , Salvia miltiorrhiza , Catharanthus roseus, Bacopa monnieri , Nicotiana tobaccum, Andrographis paniculata, Chlorophytum borivilianum, Panax ginseng, Panax notoginseng, Curcuma longa, Curcuma wenyujin , etc. ( Meng and He, 2011 ; Karthikeyan et al., 2012 ; Wang et al., 2012 ; Ma et al., 2013 ; Barnawal et al., 2016 ; Kumar et al., 2016 ; Hong et al., 2018 ; Jayakumar et al., 2019 ; Sahu et al., 2019 ; Shah et al., 2019 ; Jiao et al., 2020 ; Ray et al., 2021 ; Zheng et al., 2021 ; Mei et al., 2023 ; Salwan et al., 2023 ; Sharma et al., 2023 ; Song et al., 2023 ; Wang et al., 2023 ; Zou et al., 2023 ). Thus, unquestionably, these endophytes have demonstrated tremendous potential as a green and eco-friendly alternative for boosting food production in sustainable agricultural systems.…”