Sensitivity of Corynespora cassicola, causal agent of Corynespora target spot of tomato, isolated from tomato plants in Okayama Prefecture in 2000 and 2001 to thiophanate-methyl (T) and diethofencarb (D) was investigated using a minimum inhibitory cocentration (MIC) method and bioassay. Of 250 isolates of C. cassicola isolated from tomato fields, 188 isolates were highly resistant to T, with the MIC more than 1600 ppm, and three isolates were highly resistant to both T and D. In bioassay tests, T and D had no effect on disease after inoculation with highly resistant isolates. This report is the first on the occurrence of C. cassicola resistant to both T and D.
Sensitivity of Corynespora cassicola, causal agent of Corynespora leaf spot of cucumber, isolated from cucumber plants in Okayama Prefecture to thiophanate-methyl (T) and diethofencarb (D), and azoxystrobin (A) was investigated using the minimum inhibitory concentration (MIC) method and a bioassay. With the MIC method, 29 isolates among 193 isolates were highly resistant to both T and D. In the bioassay test, an isolate resistant to A was isolated from cucumber plants in a field. This report is the first on isolates of the causal fungus that are highly resistant to both T and D and the second report on isolates resistant to A.
Melon yellow spot virus causes yellow spots or necrosis on melon (Cucumis melo) and cucumber (C. sativas) plants in Japan. This virus belongs to the genus Tospovirus, which has a tripartite RNA genome. The complete nucleotide sequence of the largest RNA segment (L RNA) of an MYSV isolate was determined and analyzed. The L RNA segment was 8, 918 nucleotide (nt) long and had one open reading frame (ORF) in the complementary sense. Deduced amino acid sequence of the ORF was 2, 870 amino acids and contained motifs of RNA-dependent RNA polymerase. Comparison of the nucleotide and deduced amino acid sequences with those of other tospoviruses revealed that MYSV was closer to Groundnut bud necrosis virus (71.0% identity) and Watermelon silver mottle virus (70.6% identity) than other tospoviruses. The 19-nt terminal sequences in the 5' and 3' untranslated regions were incomplete inverted complementary sequences. They were not similar to those in the S RNA of MYSV, but were similar to those of the L RNA of known tospovirus species.
The sheath rot fungus (Sarocladium oryzae) of rice was isolated from seedlings, sheaths and browned unhulled rice of infected plants. The fungus was also isolated from rice stubble in infested fields, unhulled rice and hull that all remained in an open field until the following spring (early summer), but not from grass seeds or barley plants. These results indicate that S. oryzae is seedborne, and survives in unhulled rice, rice hull, and stubble in fields in winter.
Cryptotaenia japonica witches' broom phytoplasma (CJWP) and onion yellows phytoplasma (OYP) were transmitted by the leafhopper H. sellatiformis. CJWP and OYP were also detected by PCR in H. sellatiformis fed on infected plants. Latent periods in H. sellatiformis of CJWP and OYP were 13-17 days. The phytoplasmas were detected by PCR in leafhoppers at about 7 days after the start of acquisition feeding. This is the first report of the transmission of CJWP and OYP by H. sellatiformis.