Haustorial formation of the downy mildew fungus, Peronospora parasitica was observed in the root tissues of susceptible and resistant cultivars of Japanese radish (Raphanus sativus horteinsis). The growth of hyphae in the susceptible cultivar was faster than that in the resistant cultivar. Five days after inoculation, haustoria were formed in the cells of the 63rd cell layer from the inoculated layer in the susceptible cultivar, and in the cells of the 12th cell layer in the resistant cultivar. The haustoria formed in both cultivars were similar in size and shape. On the surface of haustoria spherical or hemi-spherical granules, 1.7-3.7μm in diameter, were often observed in the susceptible cultivar, while rarely observed in the resistant. The granules were stained dark blue with sudan black B and red with sudan III, and disappeared after treatment with acetone. It was suggested, therefore, that the granules consisted of a kind of neutral lipid.

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The taxonomic status of Japanese tomato crown and root rot isolates ascribed to Fusarium oxysporum f. sp. lycopersici race J3 was determined on the basis of DNA-DNA reassociation kinetics. As compared with DNA homology among races of forma specialis lycopersici, isolates of race J3 showed relatively low homology (74-88%) with isolates of other races which caused typical vascular wilts of tomato, and shared high DNA homology (96-99%) within the race. By contrast, isolates of race J3 showed high DNA homology (95-100%) with an isolate of F. oxysporum f. sp. radicis-lycopersici, but exhibited low homology (69-87%) with isolates of other formae speciales of F. oxysporum. These results suggest that the causal fungi of tomato crown and root rot in Japan, previously proposed as race J3 of forma specialis lycopersici, should be designated as a different forma specialis: F. oxysporum f. sp. radicis-lycopersici (Jarvis and Shoemaker, 1978).

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The characteristics of induced dicarboximide fungicide-resistant strains of Botrytis cinerea developed by post-cultures in the filtrates of the field resistant strains were investigated. Mycelial growth curves of these induced resistant strains were divided into three groups, which were rapid in both radial and non-radial growth, slowed down in growth transiently at about 4 days of inoculation followed by fast growth again, and poor in nonradial growth. Sporulation was scarcely observed on PSA, YGA and V8 agar media except for PSA media containing cucumber leaf (Cu-PSA). But by illuminating with BLB, it was stimulated on PSA media, but not on the other media. Pathogenicity to cucumber plants was examined by cucumber leaf disc method with the mycelia cultured on distilled water agar (WA), WA media containing glucose (GA) and GA containing inosine (IGA), respectively. Any induced resistant strain cultured on WA did not form lesion on cucumber leaf discs. Six strains cultured on GA formed non-spreading lesions (disease incidence rate; DIR=2.5-7.5%), and one strain formed spreading lesion (DIR=37.5%) on the discs. Six strains cultured on IGA formed non-spreading lesions (DIR=0-17.5%), and other ten strains formed spreading lesions (DIR>42.5%), in which four strains showed high pathogenicity (DIR=80-100%). These characteristics of the induced strains had been stable through consecutive subcultures, and were different from those of the original strains of B. cinerea.

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Two mutant strains of bacteriocin-producing Pseudomonas solanacearum, both of which derived from a virulent bacteriocin-producing strain Ps48, protected tobacco plants from bacterial wilt, when the root systems of tobacco seedlings were dipped in each suspension prior to transplanting in soil infested with virulent strain Ps29. Among them tobacco plant treated with weakly virulent bacteriocin-producing strain (OM2) gave better control than that treated with avirulent bacteriocin-producing strain (OM1). Tobacco plants primarily treated with OM2 gave effective control even after invasion of the virulent strain by root injury inoculation, whereas that treated with OM1 was ineffective. OM2 population remained constant (10⁷-10⁸ colony forming unit (cfu)/g) on rhizoplane and reached approximately 10⁷cfu/g in tobacco plant at least 16 days after treatment. Antibacterial activity was detected in water extract of stem tissue at that time. On the other hand, OM1 population declined gradually from ca. 10⁹cfu/g to ca. 10⁵cfu/g in rhizosphere, from ca. 10⁸cfu/g to ca. 10⁶cfu/g on rhizoplane by 16 days after treatment. Only ca. 10²cfu/g of the bacteria were recovered and no antibacterial activity was detected in stem tissue. Multiplication of virulent Ps29 was more effectively prevented in root system and in stem of the plant primarily treated with OM2 than that with OM1 or water-treated control. Treatment with OM2 was effective against not only Ps29 (bacteriocin sensitive strain) but also Ps48 (bacteriocin resistant strain), though disease incidence and severity of tobacco plants treated with OM2 was lower against Ps29 than that against Ps48. From these results, it was presumed that bacteriocin and other factor might play roles together in protection by OM2 from bacterial wilt.

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To determine the action site of the toxin alternaric acid, the ultrastructure of cells of susceptible tomato leaves was observed. Toxin-treated tomato leaves were subjected to conventional electron microscopy and a precipitation method for some types of ions in tissue combined with analytical electron microscopy. The earliest effect of the toxin (10μg/ml) appeared on the plasmodesmatal area where electron-dense precipitates were found at cell walls after 15min exposure time. Afterwards modification of the plasma membrane occurred near the plasmodesmata consisting of slight invaginations which did not expand remarkedly later on. Precipitation of electron-dense substances at cell walls was found at 90% and invagination of the plasma membrane at 60% of the observed plasmodesmatal sites. Magnesium-ions of tissue origin could be determined in these precipitates that indicated leaking of electrolytes. Thus, alternaric acid appears to alter the morphological and physiological characteristics of plasma membranes near plasmodesmata and thereby causes a permeability change which leads to leaking of electrolytes.

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Contents of beet necrotic yellow vein virus in roots of sugar beet were compared between moderately resistant and susceptible lines and cultivars to rhizomania. The virus was initiated to detect in rootlets of 8-day seedling by ELISA and no difference, thereafter, was found in the value from rootlets between the two lines. The value gradually increased in tap roots from 30 days after emergence and exhibited highly significant difference between the lines in upper cores of tap roots at 90 days. These results show that the difference of virus content in the cores at 90 days reflect resistance to rhizomania in field, and could be useful for greenhouse test of the resistance.

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[in Japanese]

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Bacterial leaf blight of konnyaku was artificially induced by soil or seed corm inoculation. The bacterial suspension was drenched into the soil planted with konnyaku, when leaflets were fully expanded. The disease symptom was appeared on the leaflets at 14 days after inoculation. Mulching test suggested that the pathogenic bacterium existing on the soil surface might be directly splashed to leaflets by rain drops. Pathogenic bacterium existing on the seed corm multiplied on the bract after planting, followed by the rapid multiplication on leaflet. This fact suggested that the bacterium multiplied on the bract could migrate to the leaflets which were sprouting from inside of bract.

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[in Japanese]

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[in Japanese]

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[in Japanese]

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[in Japanese]

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