Here, we report the complete genome sequence of Xanthomonas arboricola pv. juglandis DW3F3, a strong pathogenic strain isolated from blighted walnut immature fruit (Juglans regia L. cv. Qingxiang). The genome consists of a single chromosome (5,144 kb).
Walnut blight caused by Xanthomonas arboricola pv. juglandis (Xaj) is an important bacterial disease for walnut production worldwide. The objective of the present study was to characterize one endophytic bacterium, namely OFE17 from Osmanthus fragrans leaves, evaluate its potential biocontrol efficiency against the disease, and identify the probable underlying mechanisms of its function. Based on morphology, biochemical and physiological characteristics, 16S-rDNA and gyrB sequences, and antibiotic production genes, the endophyte OFE17 was tentatively identified as Bacillus sp. A disease control efficiency of up to 68.69% was observed through a biocontrol test on detached immature walnut fruits under controlled conditions. OFE17 can produce protease, cellulase, amylase, siderophores, and demonstrates phosphate dissolving ability.However, OFE17 is unable to produce extracellular lipase, IAA (indoleacetic acid), and has no nitrogen fixation capability. The active compounds of OFE17 were composed primarily non-protein compounds, and the optimum organic extraction solvent was chloroform. Through specific PCR detection, we discovered it contains the genes ituA and ituD which play a key role in active compound synthesis of iturin A synthetase. This study added a promising biocontrol agent candidate for the disease control and laid a foundation for further exploration.
Plant endophytes are great resources and potential capital in versatile application, including plant diseases biocontrol. We aimed to evaluate the antagonism of English walnut endophytic bacteria against different crop pathogenic fungi, to provide more alternatives for future disease biocontrol agents. The biocontrol capacity of thirty-six walnut endophytic bacterial isolates against the anthracnose fungus, Gnomonia leptostyla was evaluated. Fifteen isolates were tested against other five pathogenic fungi such as the cauliflower black spot pathogen, Alternaria brassicicola; the tobacco brown spot pathogen, A. alternata; the corn leaf spot pathogen Curvularia lunata; wheat Fusarium head blight pathogen, Fusarium graminearum and the cucumber anthracnose pathogen Colletotrichum orbiculare. From our results, it was observed that all the assayed strains suppressed the growth of six fungal pathogens at least 20% in petri dish. Among the endophytes, the highest inhibition rates were observed in endophytes XWR6 and XWL14 against A. brassicicola with values of 68.8 and 61.6% respectively; and the endophyte XWS7 against walnut anthracnose pathogen has the inhibition value of 60.5%. Particularly, endophytes XWS7 and XWS4 isolated from walnut stem, showed an inhibition rate above 40% in all the tested pathogens. Biochemical, physiological and phylogenetic analysis based on 16S-rDNA and gyrB sequences, allowed the identification of the fifteen endophytes at Bacillus spp. However, physiological differences and sequence diversity was observed among the isolates. These findings reveals English walnut endophytic bacteria have strong antagonism activities against crop pathogenic fungi, and show diversity in biochemical, physiological, 16S-rDNA and gyrB sequences.
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