In spontaneous and mutagen-induced mutants of Pseudomonas syringae pv. theae for EPS production and/or flagellum, EPS production was correlated with the formation of a biofilm on an abiotic surface, formation of a bacterial aggregate and survival on nonwounded leaf surface, but was not required for virulence. The presence of a flagellum was correlated with swimming motility, biofilm formation on an abiotic surface, aggregate formation on the leaf surface, survival on a wounded leaf site and propagation within the leaf tissue. In addition, interactions between EPS production and flagellum were important for biofilm formation and survival on nonwounded leaf surfaces. A factor(s) other than EPS production and flagellum was required for swarming motility, and swarming motility and virulence were strongly correlated. These data indicate that EPS production is important for survival on nonwounded leaf surfaces, and the flagellum is needed for P. syringae pv. theae to survival on the wounded leaf and to propagate within the leaf tissue.
Bacterial shoot blight (BSB) disease, caused by Pseudomonas syringae pv. theae (P.s.t.), is a major disease of tea (Camellia sinensis) in western Japan. Severe outbreaks of BSB disease are associated with cold and frost damage of the tea plant; however P.s.t. itself has no ice-nucleation activity. Because we have frequently isolated P.s.t. with ice nucleation-active Xanthomonas campestris (INAX) from lesions of BSB disease, the effects of INAX on the incidence of BSB disease were examined. A high density of INAX caused severe cold damage on tea leaves at -4°C and promoted lesion formation by P.s.t. in both cold chamber and field inoculation tests. In field conditions, INAX was isolated at high frequencies from lesions in mature lesions collected when in rainy weather, but at low frequency from young lesions in fine weather. Occasionally in naturally diseased fields, seasonal population dynamics of both P.s.t. and INAX on the phyllosphere were synchronous, and populations of both were higher during the winter. INAX were also detected in 54% of lesions collected from 56 naturally diseased fields. All data indicates that INAX often enhances the incidence of BSB disease in the field during the winter.
In May 2004, fruit rots of balsam pear (Momordica charantia L.) was found in Okinawa Prefecture, Japan. Blackish, powdery and water-soaked lesions were observed on diseased fruits. A Rhizopus species isolated consistently from the diseased fruits was identified as Rhizopus stolonifer var. stolonifer and was demonstrated to cause the disease.
Anthracnose of pitaya (Hylocereus undatus (How.) Britt. & Rose was observed in Okinawa Prefecture in 2002. Numerous conidial masses formed on the surface of water-soaked lesion on fruits. A Colletotrichum species was isolated from the diseased fruits and plants, and typical symptoms were reproduced after inoculation with the isolated fungus. The causal agent was identified as Colletotrichum gloeosporioides