The Bacillus cereus Strain EC9 Primes the Plant Immune System for Superior Biocontrol of Fusarium oxysporum

Abstract

Antibiosis is a key feature widely exploited to develop biofungicides based on the ability of biological control agents (BCAs) to produce fungitoxic compounds. A less recognised attribute of plant-associated beneficial microorganisms is their ability to stimulate the plant immune system, which may provide long-term, systemic self-protection against different types of pathogens. By using conventional antifungal in vitro screening coupled with in planta assays, we found antifungal and non-antifungal Bacillus strains that protected the ornamental plant Kalanchoe against the soil-borne pathogen Fusarium oxysporum in experimental and commercial production settings. Further examination of one antifungal and one non-antifungal strain indicated that high protection efficacy in planta did not correlate with antifungal activity in vitro. Whole-genome sequencing showed that the non-antifungal strain EC9 lacked the biosynthetic gene clusters associated with typical antimicrobial compounds. Instead, this bacterium triggers the expression of marker genes for the jasmonic and salicylic acid defence pathways, but only after pathogen challenge, indicating that this strain may protect Kalanchoe plants by priming immunity. We suggest that the stimulation of the plant immune system is a promising mode of action of BCAs for the development of novel biological crop protection products.

Bacillus cereus EC9 protects tomato against Fusarium wilt through JA/ET-activated immunity

“…in Arabidopsis (Nie et al, 2017) and tomato (Yan et al, 2002). Interestingly, Wang et al (2018) demonstrated in Arabidopsis that B. cereus AR156, which is genetically clustered within the B. cereus sensu lato group together with EC9 (Madriz-Ordeñana et al, 2022), activates pattern-triggered immunity in a SA, JA, and ET-independent manner. The PI-I and ETR4 genes are fundamental for JA-and ET-dependent signaling, respectively, and they have been reported as marker genes for related pathways in tomato-Fol interactions (Di et al, 2017;Constantin et al, 2020).…”

“…B. cereus EC9 and B. siamensis DD6 strains were previously isolated from Kalanchoe-associated materials ( Madriz-Ordeñana et al., 2022 ). The bacterial strains were grown on Luria-Bertani (LB) (Sigma-Aldrich, Germany) agar plates at 28°C for 24 h and a single colony was used to inoculate 50 ml of LB.…”

“…Recently, we reported that the antifungal B. siamensis strain DD6 and the non-antifungal B. cereus strain EC9 effectively suppressed root and stem rotting disease caused by F. oxysporum in the ornamental plant Kalanchoe ( Kalanchoe blosssfeldiana ) ( Madriz-Ordeñana et al., 2022 ). Furthermore, expression analysis of the defense-related genes PR1 and LOX2 revealed activation of a primed state in Kalanchoe when the roots were colonized by EC9.…”

Antifungal Potential of Azotobacter salinestris Strain Azt 31 against Phytopathogenic Fusarium spp. Associated with Cereals

“…In recent years, biological control of Fusarium spp. using antagonistic bacteria is gaining importance, since this biological control agent is sustainable, safe, and environmentally friendly [ 12 , 13 , 14 ].…”

“…Azotobacter salinestris , Azotobacter vinelandii , and Azotobacter chroococum are a few well-known species isolated and identified from different types of soil. These organisms have also been reported to degrade pesticides, fix atmospheric nitrogen (N 2 ), and produce plant growth hormones such as indole acetic acid and gibberellic acid, and are known for their antagonistic activity against phytopathogenic fungi, which helps in disease management of various crops [ 13 , 14 ].…”