When conidia of Cochliobolus miyabeanus were held for 5 hours at 28°C under increasing hydrostatic pressures (100-500kg/cm2), the length of germ tubes decreased with increasing pressure, and their forms changed from filamentous to elliptical to spherical. In control germ tubes the nuclei were scattered in a cell, whereas at 200kg/cm2 the nuclei were clustered. No germination occurred at 600kg/cm2 and above. When conidia which were obtained by compression at 100-700kg/cm2 as above were kept under suitable condition for germination on slide, ordinary germ tubes elongated vigorously from abnormal germ tubes and from ungerminated conidia. Percentage of abnormal branching in these germ tubes increased with increasing pressure.
When conidia of Pyricularia oryzae were compressed at 0, 500, 1, 000, 1, 500, and 1, 800kg/cm2 for 10 minutes, the germination was reduced from 97% to 16%. The infectivity of these conidia to rice leaves was correspondingly reduced. At 0-1, 000kg/cm2 the number of conidia with appressoria exceeded those with ordinary germ tubes, whereas at 1, 500 and 1, 800kg/cm2 conidia with appressoria were less than those with germ tubes. With increasing pressures (0-1, 800kg/cm2) the number of susceptible type lesions decreased from 7.5 to 0.5/10cm of rice leaf, whereas the number of resistant type lesions remained approximately constant at 1/10cm. When conidia of Cochliobolus miyabeanus were exposed to increasing pressures as above, the germination and infection were reduced, but not as much as with P. oryzae. Conidia exposed to pressures above 1, 500kg/cm2 formed smaller lesions on rice leaves than those exposed to lower pressures.
About 2% of commercial kidney bean seed (variety Topcrop) were found to be infected with the charcoal rot pathogen, Macrophomina phaseoli (Maubl.) Ashby, and an average of 6 viable microsclerotia were detected in the contaminated dirt per 100g of these seeds. The field soil of the commercial seed producing area was assessed to contain an average of 11 viable microsclerotia per g of air-dried soil, and kidney bean plants grown in the soil became infected under greenhouse conditions. Pathogenicity test of a total of 6 isolates, 2 each from seed, soil, or contaminated dirt of seed showed that soil isolates were a slightly more pathogenic than others. An average rates of disease incidence (from diseased plants, M. phaseoli was always reisolated) of these 6 isolates were 21.9% at the temperature of above 30°C, and 10.5 at 26°C. Infection rates including visually healthy plants with M. phaseoli-reisolation were 32.2% above 30°C, and 21.0% at 26°C. M. phaseoli present in commercial seed and field soil has a potential ability to become virulent pathogen under favourable conditions.
Among 50 different isolates originated from field soil, kidney bean seed, or contaminated dirt of seed tested, 5, 11, or 16 respective isolates formed pycnidia on dried hypocotyl segments placed on 1.5% water agar under artificial light of 2, 000-3, 000lux at 30°C, natural light in shade at 26°C, or at fluctuating temperature of 18-42°C, respectively. Among them, isolates no.12, no.51, and no.179 were rather excellent in pycnidium formation. Environmental conditions such as temperature and light are influencial for pycnidium formation in addition to the inherent ability of pycnidium formation in the respective isolates.
Eighteen to 23% of commercial kidney bean seeds tested failed to emerge, and 7.5-14.5% of them produced diseased seedlings when seeded in pasteurized soil. Rhizoctonia solani or Colletotrichum lindemuthianum were isolated from these diseased seedlings. Fungi associated with 3 different lots of surface-sterilized commercial kidney bean seeds (variety Topcrop) were examined to study fungal flora of these seeds. A total of 1, 036 fungal isolates obtained from 6, 390 seeds of these 3 seed lots were classified into 24 genera. The major 5 genera were Alternaria, Fusarium, Colletotrichum, Chaetomium, and Rhizoctonia, making up 86% of the total isolates. Kidney bean plants became diseased in the pasteurized soil artificially infested with Colletotrichum lindemuthianum, Rhizoctonia solani or Macrophomina phaseoli isolated from these seeds. Fusarium oxysporum showed very weak pathogenicity. One per 22-41 commercial kidney bean seeds was infected with at least one of the aforementioned pathogenic fungi.
Anastomosis phenomena among 234 isolates of Rhizoctonia solani (Thanatephorus cucumeris) indicated that 214 isolates fell into one of six groups (AG-1∼AG-6) and 20 isolates were not assigned any one of groups. In the course of hyphal contact there were three cases, a) hyphae of two isolates were attracted each other, b) hypha of one isolate was attracted by hypha of another isolate, and c) these attracting phenomena were not observed and fusion was left to chance. Anastomosis within one and the same isolate was perfect fusion. Anastomosis between isolates from the same group was imperfect or contact fusion. It was observed that the imperfect fusion resulted in the death of fused and adjacent cells. Most isolates fell into AG-1 were those from rice plant, sugar beet, and soils. Most isolates of AG-2 were from soils, flax, and Cruciferae. All isolates of AG-3 were from Solanaceae (mostly potatoes). The majority of isolates of AG-4 were from Leguminosae and sugar beet. The majority of iaolates of AG-5 were from soils. Most isolates of AG-6 were from sugar beet and soils to which sugar beets had been cultivated. It is suggested that there may be pathological and ecological differentiation in R. solani.
In relation to 6 anastomosis groups in Rhizoctonia solani (Thanatephorus cucumeris), effect of temperatures on mycelial growth, hyphal widths, numbers of nucleus and colonial appearances were studied comparatively. Most isolates belonging to the group AG-1 grew rapidly at 28°C, but slightly at 35°C. Among 6 groups they grew most rapidly (about 30mm/day) at their optimum temperatures. The tissue of sclerotium was compact. The group AG-1 includes Corticium sasakii and C. microsclerotia. Most isolates of the group AG-2 grew rapidly at 23-25°C, but not at 33°C. On the mycelial colonies of the isolates small reddish-brown sclerotia were formed in concentric zones. Most isolates of the group AG-3 grew well at lower temperature as AG-2. Their hyphal widths were largest in 6 groups. Most of this group were isolated from potatoes. Isolates of the group AG-4 were able to grow at 35°C. Their hyphal widths were narrowest in contrast to AG-3. This group is the “praticola type” and their cultural colonies are mealy. Most isolates of the group AG-5 were from soils and their macroscopic appearances were yellowish. Most of the group-AG-6 were isolates from sugar beet and soils to which sugar beets had been cultivated. Their mycelial colonies were dark-brown in color, and the tissue of sclerotium was loose. AG-1, AG-2, AG-3, and AG-4 correspond with I, II, III, and IV of Schultz, A, D, F, and C of Richter and Schneider, AG-1, AG-2, AG-3 and AG-4 of Parmeter et al., and sasakii type and web-blight type, winter crops type, potato type, and praticola type of Watanabe and Matsuda, respectively. AG-5 perhaps corresponds with B of Richter and Schneider. AG-6 corresponds with rush type and root rot type of Watanabe and Matsuda.
Aphanomyces species parasitic on cruciferous crops were isolated from 20 vegetable field soils of 6 prefectures, Nagano, Saitama, Tottori, Gunma, Kanagawa, and Iwate in Japan proper. Cultural properties, host ranges and morphology were investigated with 4 isolates (N, S, T, and G from Nagano, Saitama, Tottori and Gunma, respectively) of these Aphanomyces isolates. Of 7 families of crops tested, only cruciferous crops were attacked by the 4 isolates. Growth of isolates was good on potato-dextrose agar and radish agar, and except isolate T, methionine agar also gave considerable growth. These isolates grow between 5-35°C, with the optimum temperatures at 23-28°C. Inhibitory effect of streptomycin sulphate on growth was hardly observed at 50 and 100ppm in potato-dextrose agar. Streptomycin can be used in isolation media. From measurements of oogonia and oospores of these isolates, isolate N and S correspond to Aphanomyces raphani of Drechsler and isolate T and G correspond to A. raphani of Tsuchiya, et al. Behaviour of antheridia on oogonia agrees with the Drechsler's descriptions. Judging from the morphological characteristics and pathogenesis, these 4 isolates were identified as A. raphani Kendrick.
A virus isolated from tazetta, trumpet and large cupped narcissus plants was identified as cucumber mosaic virus, owing to the similarity in symptoms on some hosts and positive reaction with antiserum to cucumber mosaic virus Y strain in agar gel diffusion test. Another virus isolated from trumpet and large cupped narcissus plants was identified as tobacco rattle virus, owing to the similarity in host range, physical properties, particle morphology, and lack of aphid (Myzus persicae) transmission. The virus particles were found to be tubular with length showing two peaks. With an isolate obtained from trumpet narcissus plant, these were at 70-80mμ and 190-200mμ. Antiserum to this isolate prepared by injection to rabbit showed homologous precipitin tube titre of 1/512. By agar gel diffusion test, this antiserum showed negative reaction with another virus isolate obtained from trumpet narcissus plant, but positive reaction with a virus isolate obtained from large cupped narcissus. This antiserum also did not react with an aster isolate of tobacco rattle virus (TRV-A) described by Komuro et al. (1970). The third virus isolated from tazetta narcissus plant was identified as broad bean wilt virus, owing to the similarity in host range, aphid transmissibility, particle morphology, and serological reaction. The virus particles were spherical, about 24mμ in diameter. Antiserum prepared by injection to rabbit showed a positive reaction with partially purified virus and crude diseased leaf juice of inoculated broad bean plant in agar gel diffusion test. The virus showed positve reaction with antiserum to broad bean wilt virus kindly sent from Dr. R.H. Taylor.
Xanthomonas citri XCJ19, infected with temperate phage PXC7, had its smooth colony cells altered to produce dwarf colonies. The altered dwarf clones were lysogenic. After incubation in nutrient broth for 72hr, each of them reverted in 0.1-6% of its cells to produce smooth colonies, among which 60% were lysogenic, 25% resistant, and 15% sensitive. The lysogenic dwarf convertants could not be recovered to produce smooth colonies by supplements of amino acids, vitamins, or nucleic acid bases; however, they lysed and liberated spontaneously phage PXC7 at a considerably higher frequency and decreased the growth rates and the number of bacterial cells contained in the colonies, as compared with the lysogenic smooth revertants. This indicates that the lysogenic dwarf convertants have arisen from Xanthomonas citri XCJ19 as the result of the extraordinary high-frequency of spontaneous induction of the phage after lysogenization. The lysogenic dwarf convertants, though they exhibited characteristics similar to the smooth original strain on most of the tests applied, showed changes in cell disposition and response to virulent phage CP1.
Citrus seedlings of several species were sap-inoculated with viruses of satsuma dwarf (SDV) and Natsudaidai dwarf (NDV) during 1966 to 1967 by the usual carborundum method. According to the sesame test employed about 1 year after inoculation, infection occurred on 23 out of 64 seedlings inoculated with SDV or 16 out of 81 seedlings inoculated with NDV. Nine and 3 seedlings including satsuma, Natsudaidai, and Eureka lemon exhibited symptoms by infection with SDV or NDV, respectively. Thus, SDV and NDV were mechanically transmitted from citrus to citrus.