Pythium aphanidermatum in sludge from a drinking-water plant was eliminated by heat generated during composting of the sludge for horticultural use. The minimum level of heat treatment to eliminate P. aphanidermatum in the sludge in a laboratory incubator was 45°C for 7 days. Fifty m3 of the sludge in a 2.5-m high pile was mixed with a shovel loader at 3-week intervals for field tests. Inoculum of P. aphanidermatum encapsulated in a nylon screen and buried in the pile was eliminated if temperature exceeded 44°C for more than 7 days. P. aphanidermatum in naturally infested sludge was not detected 3 months after composting. Although the fungus was occasionally not eliminated because of low temperature in the sludge caused by rainfall and air temperature, covering the sludge pile with a plastic sheet maintained a high temperature in the pile. Incorporating of bark compost into the sludge (1:2, v/v) also maintained a high temperature in the pile.
Using a membrane filter and a selective medium, Burkholderia plantarii, causal agent of bacterial seedling blight, was detected in farmpond water used in a nursery affected by bacterial seedling blight. B. plantarii was detected in surface water of the farmpond, but was hardly detected in water at a depth of 2m or at the bottom of the pond. In the summer, B. plantarii was detected in the farmpond at about 300cfu/100ml at maximum, but in the winter the concentration was less than 5cfu/100ml. In several cases, however, the concentration increased drastically after stirring the water around Gramineae weeds. B. plantarii was detected from the roots of perennial Gramineae weeds in winter season, suggesting that B. plantarii may overwinter on Gramineae weeds. B. plantarii was also detected in every farmpond tested in this area. In addition, application of the farmpond water naturally containing B. plantarii at about 300 to 750cfu/100ml to seedling boxes caused seedling blight, suggesting that the farmpond water may be an important source of inoculum.
A bacterial disease that affected production of seedlings and fruits of watermelon (Citrullus lanatus) occurred in Yamagata Prefecture, Japan, in the summer of 1998. The disease was characterized by necrosis and death of seedlings; irregular brown spots with halo on the true leaves; and fruit blotch. When seedlings of watermelon were inoculated with the bacterial isolates from the watermelon at Yamagata Prefecture in 1998, irregularly shaped lesions were expressed on cotyledons and true leaves. These isolates were also pathogenic to all cucurbits tested (cucumber, pumpkin, melon, bottle gourd, wax gourd, and oriental pickling melon), tomato, and eggplant. The most sensitive hosts among them were watermelon, cucumber, pumpkin and bottle gourd. The bacteriological characteristics of the present bacterial isolates coincided with those of the standard isolates of Acidovorax avenae subsp. avenae. On the basis of bacteriological characteristics and pathogenicity, the bacterium was identified as the Acidovorax avenae subsp. citrulli (Schaad, Sowell, Goth, Colwell & Webb 1978) Willems, Goor, Thielemans, Gillis, Kersters & De Ley 1992. This is the first report of watermelon bacterial fruit blotch disease in Japan.
Soaking rice seeds in a bacterial suspension (1×108cfu/ml) of an avirulent isolate of Burkholderia gladioli (1064A) for 6 days at 15°C before sowing markedly suppressed the incidence of bacterial seedling blight caused by B. plantarii. Similarly all 16 virulent isolates of B. gladioli tested suppressed the disease, while 30 bacterial isolates belonging to the genus Acidovorax, Burkholderia (except B. gladioli), Pseudomonas and Ralstonia did not. The isolate 1064A decreased the cell number of B. plantarii co-inoculated in germinating seedlings by 1/10 to 1/100 that of the nontreated. It also markedly decreased the accumulation of tropolone, a B. plantarii toxin, in seedlings and soil. The isolate was effective against 12 strains of B. plantarii. The strain revealed a remarkable biocontrol effect when rice seeds, which have been inoculated with B. plantarii at the flowering stage and harvested in the previous season, were used as a material. Because the isolate was not virulent on 23 species of crops tested, it seems to be a promising biocontrol organism against bacterial seedling blight of rice.
A new bacterial disease of bellflower was found in Mie Prefecture, Japan, in the autumn of 1997. Brown spots on leaf blades and necrotic stripes on leaf petioles characterized the disease. Bacterial strains from bellflower induced symptoms the same as those on naturally infected plants and also induced the same symptoms found with lettuce bacterial varnish spot disease caused by Pseudomonas cichorii. On the basis of bacteriological characteristics, the bacterium was identified as Pseudomonas cichorii. This is the first report of bacterial brown spot disease of bellflower.
Gray mold was found on petioles and stems of Mitsuba (Cryptotaenia japonica Hassk.) growing in hydroponics in the summer of 1998. A Botrytis species was isolated from the infected plants. Based on the morphology and the growth temperature, this fungus was identified as Botrytis cinerea Persoon: Fries. Because a cooled nutrient solution was circulated in the hydroponic system in summer, temperature at the base of the Mitsuba plants was kept on rather lower temperature in this season. Cool weather, therefore, is required for this disease to occur during the season.
Several strains of Burkholderia glumae formed yellowish orange colonies on agar plates containing saccharides, such as glucose, ribose and arabinose. These colonies formed at 35°C or 30°C turned violet immediately after exposure to ammonia. This phenomenon was observed only in these pigment-producing strains, but not in other plant pathogenic bacteria, indicating that these strains can be used for monitoring B. glumae in ecological studies.
The full nucleotide sequence of the S RNA segment of Melon yellow spot virus (MYSV) was determined to be 3232 nucleotides long and to have every feature of the S RNAs of tospoviruses reported so far. From an amino acid sequence comparison of nonstructural proteins (NSs), MYSV is most closely related to two tospoviruses in serogroup IV. MYSV had nucleotide and amino acid sequence identities over 96% with Physalis severe mottle virus in all regions of S RNA except in an intergenic region and in deduced open reading frames, including that on complementary strand RNA.