Identification of endophytic bacterial strain GN223 and its effectiveness against citrus canker disease in navel orange under field conditions

Abstract

ABSTRACT Citrus canker caused by Xanthomonas citri subsp. citri (X. citri) is a devastating disease of citrus. In a previous experiment, bacterial strain GN223, an endophyte with the potential to serve as a biocontrol agent against citrus canker disease, was screened. In this study, strain GN223 was identified as Kosakonia cowanii by observing its morphological features, determining its physiological and biochemical characteristics and analysing the sequence of its 16S rDNA. Shaking flask fermentation conditions to grow strain GN223 were optimised using a single factor method. The results showed that the optimal culture medium for the strongest antagonistic effect on the growth of X. citri was yeast extract peptone dextrose (YPD). The optimal fermentation conditions were as follows: 50 mL of liquid (the best inoculum size was 7%) that was shaken in a 300 mL conical flask at 200 rpm for 60 h at 30°C, with an initial pH of 8. Furthermore, the ability of strain GN223 to control citrus canker disease in navel orange was evaluated. The experimental results showed that strain GN223 could positively control the citrus canker in new shoots of navel orange seedling and adult trees and young fruits in field trials. The treatment with a bacterial suspension diluted 50-fold on citrus canker in seedling and adult navel oranges resulted in control by approximately 40.0% and 50.1%, respectively. And the effect of strain GN223 on the incidence of canker on young fruits of navel orange did not differ significantly from that of copper hydroxide.