To elucidate the role of Kouyawarabi (Onoclea sensibilis L.), a weed in the environs of paddy fields as an inoculum source of Burkholderia plantarii, the pathogen of bacterial seedling blight of rice, We investigated transmission of the pathogen from the time inoculated rice seedlings were transplanted into fields until seeds were harvested during the next crop season. Although seeds harvested from the diseased transplants were not contaminated, a few infested seeds were harvested from the hills distant to the transplant area. However, the bacterium was not detected from rice stublle the next spring or from seeds harvested from rice plants grown in the sites that held the transplanted diseased seedlings during the previous year. Numerous infested seeds were obtained from rice plants grown in pots irrigated with rainfall runoff from leaves of Kouyawarabi infected with B. plantarii, however, the resultes varied from year to year. To follow the bacterium from the weed to rice plants, we used a rifampicin-resistant strain of the bacterium. The bacterium clearly was carried in the rainfall from lesions on Kouyawarabi leaves, survived in the irrigatation water and was then detected in tissues of rice plants until harvest. Additionally, seedlings that developed from infested rice seeds had typical symptoms of bacterial seedling blight in nursery boxes. Both rice seedlings and Kouyawarabi contaminated with B. plantarii play an important role as inoculum source of bacterial seedling blight of rice during unfavorable weather for growing rice plants.
We investigated DIBA and TPI techniques to detect Acidovorax avenae subsp. citrulli (Aac), the causal agent of watermelon bacterial fruit blotch from diseased plant materials. Direct DIBA used conjugate that was a conjugant of anti-Aac-IgG and alkaline phosphatase. The detectable limit of direct DIBA was about 106cfu/ml, when cultured Aac suspension was used as antigen. Strong positive reactions were obtained for only Aac by direct-DIBA and TPI techniques. Weak positive reaction was obtained for 1 or 2 strains of A. avenae subsp. avenae and Pseudomonas cichorii with a bacterial suspension of about 108cfu/ml. Strains of other plant pathogenic bacteria did not react. To detect Aac from symptomatic plant tissue, sections from symptomatic areas were macerated with phosphate-buffered saline in micro test tubes, and the result out supernatants tested by direct DIBA technique. When detection was carried out with the TPI technique, the sections from diseased plants were applied directly to the membrane filter. When diseased nursery plants obtained from infested seeds were tested by the direct DIBA and TPI techniques, positive reactions were obtained from all symptoms caused by Aac (isolated by dilution plate technique with selective medium AacSM). Moreover, positive reactions were obtained from old symptoms over 28 days after inoculation, and Aac was not isolated by the dilution plate technique using AacSM. Only about 30min/sample was needed to detect Aac by the direct-DIBA technique and 60min/50 samples was needed. From the results mentioned, direct-DIBA and TPI techniques are rapid and simple techniques for detecting of Aac from diseased plant materials.
This study investigated Pyricularia oryzae infection of seeds harvested from seed production fields, the role of infected seeds in seedling blast occurrence, and effective methods for disinfecting infected seeds for the purpose of developing control methods for seedling blast caused by infected seeds. Infection intensity in fungus-infected seeds was tested with the Brotter method. About 20% of seeds, in which sporulation was observed with a stereomicroscope, showed invasion by the fungus into the rice husk. From results of periodical observation on fungus-infected seeds from the heading to late reaping the stage of infection in brown rice and the invasion process within rice seeds was determined. Blast-infected seeds harvested at the late reaping were neither removed by specific gravity with salt, nor disinfected with some seed disinfectant agents. The heavily infected seeds developed seedling damping-off and abundant sporulation at the base of the seedling stem 40 days after sowing. Two methods were able to disinfect the pathogen in infected brown rice seeds: the vacuum method with disinfectant chemicals, and hot water immersion.
To evaluate the efficacy of multilines in rice blast control, panicle blast severity was evaluated for Sasanishiki near-isogenic lines after inoculation with a virulent isolate with or without pre-inoculation with an avirulent blast isolate. Disease severity generally differed among lines, high for Sasanishiki BL No.6, moderate for No.3 and low for No.4. The disease on Sasanishiki BL No.4 was suppressed when panicles were pre-inoculated with a high concentration of an avirulent spore suspension (2.5×106spores/ml). However, this suppression was not observed on Sasanishiki BL No.3 or No.6.
From lettuce (Lactuca sativa L.) with big vein symptoms, two bands were detected by Western blot analysis using antisera to Tobacco stunt virus and Tulip mild mottle mosaic virus (As-TMMMV), respectively. One band reacted to antiserum to Mirafiori lettuce virus (MiLV) stronger than As-TMMMV. Unstable filamentous Ophiovirus-like particles (LBV-O) decorated with As-TMMMV in immunogold labeling were observed along with Lettuce big-vein virus-like rod-shaped particles in diseased plants. Manual inoculation with lettuce sap caused chlorotic local lesions in Chenopodium quinoa and systemic infection in lettuce. Along with LBVV, LBV-O was transmitted by Olpidium brassicae. LBV-O was identified as MiLV for the first time in Japan.
Seedlings of garland chrysanthemum, Chrysanthemum coronarium L. var. spatiosum L.H. Bailey, developed damping off in hydroponics in the summer. The causal agent was identified as Pythium ‘group F’ and P. myriotylum, and the disease named damping off or tachigare-byo.