Abstract
Antibacterial substances were produced in the citrus leaves inoculated with Pseudomonas sp. which was known as a bacterium antagonistic to the symptom development of citrus canker. The crude extracts from the leaves inoculated with cell suspension of Pseudomonas sp. (A-ex), or mixture of Pseudomonas sp. and Xanthomonas campestris pv. citri (AX-ex) remarkably inhibited the growth of X. campestris pv. citri, whereas the crude extract from the leaves inoculated with X. campestris pv. citri alone (X-ex) showed week inhibition. Several fractions of A-ex by thin layer chromatography (TLC) on a silica gel plate markedly inhibited the growth of X. campestris pv. citri. From these fractions, two inhibitory substances, CLP-3 and CLP-5, were isolated by TLC with two developing solvent systems. The concentrations of these two substances were extremely high in A-ex and AX-ex, but very low in X-ex. The substances showed higher antibacterial activity against Pseuomonas sp. than X. campestris pv. citri. It suggests that these substances might be phytoalexins. These antibacterial substanes produced by inoculation of Pseudomonas sp. are considered to play some important roles in the mechanisms of the inhibition toward development of citrus canker.
