ISOLATION AND CHARACTERIZATION OF XANTHOMONAS AXONOPODIS CAUSING CANKER DISEASE OF LIME TREE AND EVALUATION OF ABILITY OF EXTRACTION FROM STEM OF EUPHORBIA TIRUCALLI AGAINST X. AXONOPODIS

Tóm tắt

Bacterial citrus canker is one of the major causes of yield losses in citrus growing areas of the world. Xanthomonas axonopodis is the cause of this disease on lime tree which badly affects the plant health and fruit quality. In this study, 25 samples of lime tree canker were collected from Ben Luc district, Long An province in Vietnam. The bacteria were isolated from infected samples and identified base on the biochemical characteristics such as Gram staining, starch hydrolysis, Tween 80 hydrolysis, gelatin liquefaction, KOH test, Kovacs’ oxidase and catalase test. The results showed that canker disease of lime tree caused by X. axonopodis. Furthermore, aqueous, ethanol, methanol, acetone and diethyl ether extracts from stem of Euphorbia tirucalli were used to evaluate antagonistic ability against X. axonopodis using agar well diffusion method. The results revealed that methanol stem extract showed highest antibacterial activity with zone of inhibition 25.67 ± 0.47 mm after 48 hours of incubation. The minimal inhibitory concentration for the methanol extract was 8-32 mg/mL for all of the bacteria. The diethyl ether extract did not show activity against the tested pathogenic bacteria. To our knowledge, this study was the basis for the application of plant extracts to manage lime tree canker and disease of other crops cause by X. axonopodis.

Keywords: Euphorbia tirucalli, canker disease, antibacterial activity, methanol extract.