Crucifer strains of Olpidium brassicae were isolated from the soil in cabbage fields for the first time in Japan. Initial bulk-cultures developed resting spores, but single-sporangium isolates (CBG-1 to 5 and YR-1 to 4) did not. Resting spores formed after mixed inoculation with the isolates. The results confirmed the assumption by Sahtiyanci (1962) that Pleotrachelus brassicae (=O. brassicae) is hetellothallic. On the other hand, of five single-sporangium isolates of noncrucifer strains from fields of welsh onion (WOms-3), tobacco (TAK-1), lettuce (LE-4, WT-1) or soybean (F-1), three (WOms-3, LE-4, WT-1) were a vector of lettuce big-vein and developed resting spores without mating. The distribution of resting spores in their first generation varied depending on the infection sites and host plants. These results indicated that the manner of resting-spore formation differed between crucifer and noncrucifer strains, suggesting that both strains were distinct species as suggested by Sahtiyanci (1962).
Benzimidazole-resistant strains isolated from anthracnose-affected leaves of Japanese pear were not negatively correlated with cross-resistance to diethofencarb. Based on this, the strains were thought to perhaps be Colletotrichum acutatum, which is inherently insensitive to both benzimidazoles and diethofencarb. However, morphological studies and polymerase chain reaction using primers that specifically amplified the internal transcribed spacer 1 region of ribosomal DNA of C. gloeosporioides and C. acutatum, showed that the strains were intermediately benzimidazole-resistant of C. gloeosporioides. EC50 of benomyl for mycelial growth of the strains was around 15 ppm, an intermediate value between that for sensitive strains and highly resistant strains. The deduced amino acid at codon 200 was altered from phenylalanine (TTC) to tyrosine (TAC), based on sequence analysis for the β-tubulin gene. Control efficacy of benomyl against intermediately benzimidazole-resistant strains was low in inoculation tests.
From lettuce (Lactuca sativa) leaves with big-vein symptoms, two viruses associated with lettuce big-vein, Mirafiori lettuce virus (MiLV) and Lettuce big-vein virus (LBVV), were isolated. To make clear which virus is really associated with big-vein symptoms expression, the effect of the growth temperature for lettuce, on the serological detection of the two viruses and symptom expression was analyzed. At 27°C, LBVV was detected in the leaves, but neither the big-vein symptoms nor MiLV were observed. When the growth temperature was decreased to 18°C, big-vein symptoms appeared and MiLV was detected in the leaves.
Leaf sheath rot of rakkyo plants (Allium chinense G. Don) has been observed in Chiba Prefecture since 1990. Lerf blades became reddish and underground parts of leaf sheaths rotted. A Fusarium species was isolated from the diseased leaf sheaths and typical symptoms observed in nature were reproduced by inoculation. The casual agent was identified as Fusarium avenaceum (Fries) Saccardo.