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.

摘要

由柑橘黄单胞菌引起的柑橘溃疡病。柑橘（X. citri）是柑橘的一种毁灭性病害。在之前的一项实验中，筛选了细菌菌株 GN223，这是一种内生菌，具有作为柑橘溃疡病生物防治剂的潜力。本研究通过观察其形态特征、生理生化特征及16S rDNA序列分析，将菌株GN223鉴定为Kosakonia cowanii。使用单因素方法优化培养菌株 GN223 的摇瓶发酵条件。结果表明，最佳培养基对柑桔黄腐病的生长拮抗作用最强是酵母提取物蛋白胨葡萄糖(YPD)。最佳发酵条件如下：将 50 mL 液体（最佳接种量为 7%）置于 300 mL 锥形瓶中，在 30°C 下以 200 rpm 的速度振荡 60 h，初始 pH 值为 8。此外，评估了菌株 GN223 控制脐橙柑橘溃疡病的能力。试验结果表明，菌株GN223在田间试验中对脐橙幼苗和成树及幼果的新梢柑橘溃疡病有积极防治作用。用稀释 50 倍的细菌悬浮液处理幼苗和成年脐橙的柑橘溃疡病，分别导致控制率分别约为 40.0% 和 50.1%。并且菌株GN223对脐橙幼果溃疡病发生率的影响与氢氧化铜没有显着差异。