Endophyte Bacillus velezensis Isolated from Citrus spp. Controls Streptomycin-Resistant Xanthomonas citri subsp. citri That Causes Citrus Bacterial Canker

Abstract

Citrus bacterial canker (CBC), caused by the plant pathogenic bacterium Xanthomonas citri subsp. citri (Xcc), is a devastating disease in many commercial citrus cultivars. Every year, CBC causes a substantial reduction in fruit quality and quantity that corresponds to significant economic losses worldwide. Endophytic microorganisms produce numerous bioactive secondary metabolites that can control plant pathogens. We investigated the antagonistic activities of 66 endophytic bacteria isolated from nine citrus cultivars to control streptomycin-resistant Xcc. The suspension of Endophytic Bacteria-39 (EB-39), identified as Bacillus velezensis, exhibited the highest antibacterial activity against three wild-type and six streptomycin-resistant Xcc strains, with the inhibition zones between 39.47 ± 1.6 and 45.31 ± 1.6 mm. The ethyl acetate extract of EB-39 also controlled both wild-type and streptomycin-resistant Xcc strains, with the inhibition zones between 29.28 ± 0.6 and 33.88 ± 1.3 mm. Scanning electron microscopy indicated the ethyl acetate extract of EB-39-induced membrane damage and lysis. The experiments using the detached leaves of a susceptible Citrus species showed that EB-39 significantly reduced the incidence of canker on the infected leaves by 38%. These results strongly suggest that our newly isolated EB-39 is a novel biocontrol agent against CBC caused by wild-type and streptomycin-resistant Xcc strains.

Isolation of the Novel Strain Bacillus amyloliquefaciens F9 and Identification of Lipopeptide Extract Components Responsible for Activity against Xanthomonas citri subsp. citri

“…In particular, different Bacillus spp. have shown biocontrol effects on Xcc such as in vitro inhibition of growth [ 23 ] or by lysis of bacterial cells [ 5 , 24 ]. The application of B. subtilis WG6-14 and TKS-1 24 h prior to Xcc inoculation was able to reduce citrus canker development in Citrus aurantifolia [ 25 ].…”

Transcription factor WRKY22 regulates canker susceptibility in sweet orange (Citrus sinensis Osbeck) by enhancing cell enlargement and CsLOB1 expression

“…Citrus canker, induced by Xanthomonas citri subsp. citri (Xcc), is one of the most serious diseases facing the global citrus industry 1 , 2 . The key pathogenic factors and the molecular mechanisms of the host response to Xcc are not well understood 3 – 5 , which severely limits the progress of citrus disease resistance breeding.…”

Citrus Canker Pathogen, Its Mechanism of Infection, Eradication, and Impacts

“…Many endophytic bacteria act as biocontrol agents and positively affect the growth of host plant [ 154 ]. For biocontrol of citrus canker, many strains of endophytic bacteria such as Burkholderia cepacia [ 155 ], Bacillus velezensis [ 156 ], Bacillus amyloliquefaciens [ 157 ], Kosakonia cowanii [ 158 ], Bacillus subtilis [ 159 ], and Bacillus thuringiensis [ 160 ] have shown fruitful results. Bacillus strains have been proven very effective for canker control [ 159 ].…”