The seasonal process of infection and propagation of wheat yellow mosaic virus (WYMV) in winter wheat (Triticum aestivum L.) was studied in a field in Morioka, Japan. In the susceptible winter wheat cultivar Nanbukomugi, WYMV was first detected by ELISA only in roots on November 30, about two months after seeding in a field naturally and seriously infested with the virus. The incidence and concentration of the virus in roots and shoots of Nanbukomugi then increased when temperatures dropped below 5°C and with snow cover, and reached a high level before snow melt. Disease incidence in the cultivar in the same field was 96% when wheats were sown at the usual time. In contrast, in the resistant cultivar Hachimankomugi was asymptomatic and virus incidence was low during the same period. In a cross-transplanting test between infested and non-infested fields, virus infection occurring from mid-October through early November in Nanbukomugi resulted in symptom expression in spring. These results suggest that WYMV, infecting during the conducive period, propagated under low temperature conditions which induced a high virus incidence and concentration in the susceptible cultivar before symptoms were expressed, thus resulting in a high disease incidence.
Control of an important paddy weed, annual Echinochloa spp. by inoculation with its pathogens was investigated under greenhouse conditions. Isolates of Exserohilum monoceras, E. rostratum, Bipolaris sorokiniana, Curvularia lunata, C. aeria, Colletotrichum graminicola, Pyricularia grisea, and Ustilago trichophora were obtained from diseased Echinochloa spp. collected in Japan. After selecting the most virulent isolate of each species, eight representative isolates were compared for their weed control activity against E. crus-galli var. crus-galli long awn biotype, using spray and drop inoculation. E. monoceras and C. lunata reduced the dry weight of plants by over 80 percent using both types of inoculation. Drop inoculation resulted in higher weed control than spray inoculation. E. monoceras exhibited high herbicidal activity against E. crus-galli var. crus-galli (long and short awn biotypes), E. crus-galli var. ƒormosensis, E. oryzicola and E. colona which grow in Japanese paddy fields. C. lunata, however, exhibited low herbicidal activity against E. crus-galli var. ƒormosensis and E. oryzicola.
Non-pathogenic Fusarium oxysporum S3HO3, isolated from the root surface of healthy spinach growing in a field infested with Fusarium wilt, cross-protected against F. oxysporum f. sp. spinaciae, when the soil was amended with the isolate before infestation with the pathogen. This cross-protection, however, did not continue through the harvesting. In order to extend the duration of disease suppression, pre-treatment of spinach seedlings with non-pathogenic F. oxysporum S3HO3 was combined with subsequent transplanting to reduce disease development. The most effective pre-treatment method for seedlings was mixing a bud-cell suspension (106 cfu/dry soil g) with nursery soil before sowing and then seedlings were grown 15 days before transplanting. Disease suppression then lasted through harvesting with a protective value of 96.3 when pre-treated seedlings were transplanted in infested soil. On the other hand, when nursery soil was drenched with a bud-cell suspension (107 budcells/ml, 1/10, v/w) 10 days after sowing (5 days before transplanting) and pre-treated seedlings were transplanted, the protective value (87.1) was higher than drenching at earlier stage such as 1 or 5 days after sowing. Although the drenching method was easier and more practical, its protective value was less than that of the soil-mixing method. Non-pathogenic F. oxysporum S3HO3 was not pathogenic to spinach, cucumber, melon, water-melon, tomato, lettuce, garland chrysanthemum, carrot, Japanese hornwort and some Brassica spp. Practical control of Fusarium wilt of spinach by transplanting seedlings grown in nursery soil containing non-pathogenic F. oxysporum S3HO3 was tested in the field. The protective effect of this method was even greater than that obtained by direct sowing, more effective than transplanting without inoculation with non-pathogenic F. oxysporum S3HO3 and as effective as solar heating sterilization in a closed vinyl house in summer, when pre-treated seedlings were transplanted in naturally infested soil in vinyl house. The protection in the field lasted through harvesting. These results suggest that control of Fusarium wilt of spinach by transplanting spinach pre-inoculated with non-pathogenic F. oxysporum S3HO3 should be practical.
Isolates of Colletotrichum higginsianum Sacc. and C. gloeosporioides (Penz.) Penz. et Sacc. were grouped into three genotypic species based on arbitrarily primed PCR with primer of the repetitive motifs (CAG)5. One group consisted only of C. higginsianum isolates. The other two groups contained isolates of C. gloeosporioides and excluded C. higginsianum. These results may support Sutton's consideration that C. higginsianum is not a synonym of C. gloeosporioides.
Gray mold disease of clematis was found from 1995 to 1997 in the garden of Osaka Agricultural Forestry Research Center. Typical symptoms were leaf spot and tip burn of leaf, with the spots sometimes having zonate rings. Many spores appeared on the leaf spots under humid conditions. A Botrytis species was consistently isolated from the infected leaves. The conidiophore of the fungus was apically branched. The conidia were about 8-16×5-10μm (mostly 9-13×6-8μm) under SEM, many micro-projections appeared on the surface of conidia. The fungus infected eggplant and tomato leaves and strawberry fruits. Symptoms on inoculated plants were similar to those of gray mold disease caused by Botrytis cinerea. The fungus from clematis was identified as Botrytis cinerea Persoon: Fries based on morphological and cultural studies.
The flocculation test using high density latex (HDLF) which gives a reaction figure very similar to that of sensitized sheep red blood cells was established for simplified detection of rice stripe virus from infected rice plants and viruliferous insect vectors. Furthermore, six other plant viruses such as rice dwarf virus, odontoglossum ringspot virus, cymbidium mosaic virus, turnip mosaic virus, carnation mottle virus and cucumber mosaic virus were detected by HDLF of each infected host. These dilution end points for the positive reaction of sap were 1:8×103 to 1:16×103. Though weak non-specific reactions of HDLF were observed in sap from some healthy plants, they could be prevented by diluting sap more than 1:100.
A specific growth inhibitor of Pseudomonas solanacearum, 3-indolepropionic acid, was tested for its effect on bacterial wilt of tomato in a hydroponic culture system. The compound had no apparent adverse effect on tomato plants at concentrations below 10μg/ml and completely protected tomato plants from wilting at 5-10μg/ml in the presence of 108cfu/ml of the pathogen. The compound was found to be glucosylated in tomato plants, suggesting that it could be used as a control agent of bacterial wilt for large scale hydroponic tomato culture.