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.
Highlights
Citrus species are fruit crops that can be found worldwide, and they have high value in both fresh and processed fruit industries [1]
Citrus fruits are very popular worldwide for their flavor, and they are the source of secondary metabolites, such as flavonoids with anti-inflammatory and antimicrobial activities
Primary Screening of the Endophytic Bacteria Isolated from Citrus spp
Summary
Citrus species are fruit crops that can be found worldwide, and they have high value in both fresh and processed fruit industries [1]. Citrus fruits are very popular worldwide for their flavor, and they are the source of secondary metabolites, such as flavonoids with anti-inflammatory and antimicrobial activities. Flavonoids, such as hesperetin, naringenin, eriodictyol, and isosakuranetin, have been investigated for their possible roles in the prevention of life-threatening cardiovascular diseases and cancer [3]. Citrus bacterial canker (CBC) is the most severe and contagious disease of Citrus spp. and cultivars [4,5,6]. The severity of this disease was first reported around 1912 in Florida, and it spread throughout the U.S as a result of imported seedlings from Japan [4]. CBC type A (Asiatic type of canker) caused by X. citri subsp. citri (Xcc), previously named X. axonopodis pv. citri, is the most destructive and widespread form of the disease in
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