Pseudomonas cichorii, Ps. marginalis pv. marginalis, Ps. viridiflava, Xanthomonas campestris pv. vitians and Erwinia carotovora subsp. carotovora were isolated from diseased lettuce of various localities in Japan, and their resistance to streptomycin was investigated in vitro. Two point seven percent of Ps. cichorii isolates and 3.6% of Ps. viridiflava isolates were highly resistant to streptomycin (minimal inhibitory concentrations at 200 and 400ppm, respectively), and 9.1% of the latter was moderately resistant (at MIC 25 to 100ppm). The MIC for 7.7% of the isolates of E. carotovora subsp. carotovora was within the range of 50 to 100ppm. None of the isolates of Ps. marginalis pv. marginalis and X. campestris pv. vitians was resistant to streptomycin.

View full abstract

The frequency of emergence of resistant strains in vitro and the acquisition of resistance to streptomycin by a successive culture in media containing streptomycin were investigated using Pseudomonas cichorii, Ps. marginalis pv. marginalis, Ps. viridiflava, Xanthomonas campestris pv. vitians and Erwinia carotovora subsp. carotovora. The resistance was induced by the successive passages through media which contained gradually increasing concentrations of streptomycin in Ps. marginalis pv. marginalis, Ps. cichorii, Ps. viridiflava and E. carotovora subsp. carotovora, which became resistant at 800ppm of streptomycin after 5, 6, 6, and 8 transfers respectively. No resistant strains of X. campestris pv. vitians were obtained after 8 times of transfers. The frequencies of emergence of spontaneous resistant strains to streptomycin were 1/10⁷ for Ps. marginalis pv. marginalis, and 1/10⁸ for Ps. viridiflava and E. carotovora subsp. carotovora. Such strains were not found in Ps. cichorii and X. campestris pv. vitians.

View full abstract

Potato tuber disks, 15mm in diameter and 1mm thick, Which had absorbed ⁸⁶RbCl, Were inoculated by incompatible and compatible races of Phytopthora infestans. At intervals, leakages of ⁸⁶Rb⁺ from the infected disks were determined. The leakage of ⁸⁶Rb⁺ was accelerated by infection with the incompatible race in an early stage of infection, at which hypersensitive death of the infected cells had not yet occurred. The acceleration rate was not great, but statistically significant. There was, on the contrary, no difference in leakage of ⁸⁶Rb⁺ between control and the disks infected by the compatible race. ⁸⁶Rb⁺-labelled disks were immersed for 10min in a suspension of water-insoluble zoosporial component (C-fr, sugar content, 30μg/ml). At intervals, leakages of ⁸⁶Rb⁺ from the treated disks were determined. The results showed that C-frs of both the compatible and incompatible races reduced greatly the release of ⁸⁶Rb⁺. Effects of infection opposite to that of C-fr suggested that the latter, as it is, may not be the very cause of the hypersensitive response in potato late blight, or that C-fr may not induce the proper response of hypersensitivity, when the disks were treated by the method used in the present experiments.

View full abstract

Seven Pythium species; ie. P. acanthophoron, P. irregulare, P. myriotylum, P. spinosum, P. paroecandrum, P. ultimum, and an unidentified Pythium sp., were isolated from the hypocotyls, roots, rhizosphere and/or non-rhizosphere soils of bean plants grown in the experimental plots of monoculture and rotation in Hokkaido Prefectural Kitami Agricultural Experiment Station. Among these, Pythium myriotylum was found only from the monoculture plots. The bean plants grown in the monoculture plots were colonized by above mentioned seven species of Pythium, while those in the rotation plots by P. spinosum, P. paroecandrum, and P. ultimum. In inoculation tests with five Pythium spp. except P. acanthophoron and P. irregulare which were rarely isolated, P. myriotylum and Pythium sp. were the most pathogenic to bean seedlings, followed by P. spinosum. Other two Pythium spp. have poor pathogenicity.

View full abstract

The bean plants in monoculture plots in Hokkaido Prefectural Kitami Agricultural Experiment Station showed severe necrosis of roots and retarded the growth in the middle of July in 1979, while those in 6-year rotation plots seemed healthy. The height and yields of bean plants in monoculture were about 80% and 70% of those in rotation. These appearences are said to be caused by the long-term monoculture. Pythium myriotylum and an unidentified Pythium sp., highly pathogenic to bean plants, were isolated only from the necrotic root tissues in monoculture. P. spinosum, P. paroecandrum and P. ultimum, mildly or scarcely pathogenic to bean plants, were recovered from the roots in moculture and also those in rotation. Populations of P. myriotylum and Pythium sp. in rhizosphere and nonrhizosphere soils of bean plants in monoculture were remarkably high. There was no difference in the populations of the other Pythium spp. in the soils of monoculture and rotation. When ridomil, N-(2, 6-dimethylphenyl)-N-(methoxyacetyl) alanine methyl ester, which is one of the selective fungicides against Oomycetes, was drenched to the soil collected from the monoculture plots, the roots of bean seedlings grown in the soil remained healthy as those in the untreated rotation soil. These results suggest that the symptoms of bean plants in monocuture are caused by the infections of P. myriotylum and an unidentified Pythium sp.

View full abstract

An action spectrum for photoinduced conidium formation in the fungus Alternaria solani (Ellis et G. Martin) Sorauer was determined by exposing colonies to monochromatic radiation obtained from a diffraction grating monochromator. Reciprocity holds over a wide range of time and dose rate for wavelengths of 242 and 283nm. The most effective wavelength is around 230nm. Three peaks are evident in the action spectrum at around 230, 270 and 285nm, with definite shoulder at about 303nm. Another shoulder is dsicerned at around 240nm. The main trough is at 250 to 260nm. Wavelengths longer than 356nm were not effective in inducing conidium formation even at high dosages given by 6hr continuous irradiation.

View full abstract

Vital staining by uranine on conidia or mycelia of Erysiphe graminis f. sp hordei was investigated. When conidia blown onto glass-slides or mycelia developed on primary leaves of barley cultivar, Trebi I, were stained, brilliant green fluorescence was observed in both conidia and mycelia under a fluorescent microscope. Cytoplasm in living cells was the site of uranine-accumulation. No inhibitive effect of uranine on spore germination or mycelial growth was observed. Autoclaved conidia and mycelia with disorganized cytoplasm showed dull yellow fluorescence. Fluorescent intensity of uranine in these cells decreased rapidly by 7-8min NUV-irradiation of B-excitation light from the fluorescent microscope and brilliant green fluorescence changed into dull yellow with disorganization of conidial or mycelial cytoplasm for about 5min irradiation. These results suggested that living conidia or mycelia of E. graminis f. sp. hordei showed brilliant green fluorescence in the organized cells and could be distinguished from dead ones showing dull yellow fluorescence. In conclusion, the present method is proved to be available for investigation on vital behavior of parasitic cells in the tissues of host-parasite interaction in vivo.

View full abstract

The relationship between cytoplasmic responses, especially fluorescence appearance in papillae, epidermal cells, and mesophyll cells, in powdery-mildewed barley leaves and vital behavior of conidia or mycelia of Erysiphe graminis f. sp. hordei, race I, were studied using uranine staining which was reported in the previous paper. The change of fluorescence color of uranine and disorganization of cytoplasm were employed as a marker to distinguish living fungi, showing brilliant green fluorescence (BGF) of uranine, from dead ones, showing dull yellow fluorescence (DYF). At primary infection sites, about 50% of inoculated conidia were killed by well-developed fluorescent papillae 48 hr after inoculation. At small papillae without fluorescence, conidia showed BGF of uranine and branching another infection lobes from appressoria. The occurrence of epidermal fluorescing was parallel to the resistant degrees expressed in multiallelic lines, and in all lines, about 90% of conidia which caused epidermal fluorescing were killed 24hr after inoculation. When the normal haustoria were formed, the fluorescence appearance in mesophyll cells was observed in three resistant lines (Heil's Hanna, Turkey 290, and Black Russian). In these lines, the occurrence of DYF and disorganization of cytoplasm (DOC) in mycelia corresponded to the resistant degrees. In a resistant line, A. 222, when fluorescing at the secondarypenetrated epidermal cells occurred rapidly, more than 50% of pustules showed DYF and DOC 48 and 72hr after inoculation. The pustule elongated secondary hyphae to reach the sporulation when the epidermal fluorescing did not occur. These results suggested that the fluorescent compounds postinfectionally produced in host cells had a fungicidal effect on the fungus.

View full abstract

Effect of rainfall on the development of angular leaf spot of cucumber was investigated in an experimental field equipped with artificial rainfall facilities. Daily artificial rainfall for 30 minutes resulted in severe development of angular leat spot, and the percentage of infected leaves showed twice as much as that of cucumber grown in check plots, although the humidities of both rainfall and check plots were maintained in almost similar conditions during the experimental period. The rain water dripping from the diseased leaves contained the pathogen in concentration of 10⁵-10⁶ cells per ml of raindrop during 5-10 minutes after the beginning of the artificial rainfall. Typical symptoms of the disease also appeared on seedlings, when those were exposed to the dripping rain water from the diseased leaves for 3 minutes and kept in moist chamber for 2 days. From the results mentioned above, it was supposed that the facilitative effect of rainfall on the progress and development of angular leaf spot was principally due to the transmission of causal bacteria with raindrops. In order to control the disease by means of culturing method, cucumber vines grown in field were sheltered by roof of plastic film. As the result, development of the disease was reduced to such a light degree of disease showing only marginal small lesions on leaves as seen in Fig. 2. So, we concluded that cultivation of cucumber avoiding rain under plastic roof was very effective on the control of angular leaf spot.

View full abstract

Cross-protection of the cucumber anthracnose by a hypovirulent strain of Fusarium oxysporum f. sp. cucumerinum was examined for seedlings of cucumber cvs. Suyo and Shogoin-Fushinari. Number and size of anthracnose lesion on first true leaf were reduced in both cultivars by the introduction of microconidia from hypocotyl cut-ends 2 to 4 weeks before the challenge inoculation with Colletotrichum lagenarium. Dipping of the cut-ends for 2hr into microconidia suspension at 2×10⁴ spores/ml was sufficient to reduce the anthracnose lesions. The inducer fungus survived mainly in hypocotyl and root, and no fungus was detected in the challenge site. This indicates that the induction of systemic resistance occurs at “hypocotyl and root to leaf” level. It was suggested by the experiments with culture filtrate and cell free fractions of budding spores that the systemic resistance is induced without agents which cause damage characteristic of Fusarium wilt, such as wilting and browning of vascular system. Cell wall fraction which was removed water soluble materials by autoclave was most effective to induce the systemic resistance.

View full abstract