Nuclear phenomenon of the fungus, Phytophthora capsici Leonian, has been examined at the sporangial stage in two types of germination. Nuclei in sporangia, in germ-tubes, and in zoospores stained well with a modified HCl-Giemsa technique. Distinct differences with regard to the appearance of nuclei (DNA) in the germinating stage were observed. There are two groups of sporangia which differ in form and number of the nuclei. In one group, the nuclei are globate and large, varying between 3 and 28 in number. In the other group, the nuclei are more elongate and small, varying from 23 to 49 or more in number. In the former group, there is a high correlation between the number of globated and large-sized nuclei and the length of sporangia, but it is not so in the latter group. Number of zoospores in the former group sporangium ranges from 8 to 28. When zoospores are released from sporangium, they are still uninucleate. These may result in indirect germination. In the other group of sporangia, however, zoospores retain polynuclear condition for a long time, and this seems to cause direct germination. The occurrence of these large and small nuclear types is in a proportion of 83.9:16.2. These facts are in accord with the data given by numerous studies relating an appearance of the two types of sporangial germination. The two types of sporangial germination proved the inherent nature of their occurrence having for their rates 83.9 and 16.1 for indirect and direct germination of sporangium, respectively.
1) In recent years, a mosaic disease of lettuce has been recognized in the vicinity of Tokyo as one of the most destructive diseases of lettuce. Symptoms on crisp-head type varieties, Imperial 847 and Great Lakes, are conspicuous, leaves becoming distorted and frequently developing mosaic or vein-clearing. In butter-head type variety, Wayahead, very faint mosaic or vein-clearing, and in some individuals, necrotic flecks are observed. 2) Twenty-three collections of mosaic lettuce plants were tested for the causal viruses by inoculating with carborundum to several indicator plants. As a result, 4 samples yielded cucumber mosaic virus, while the other 19 samples were found to contain a virus hitherto unreported from Japan. 3) This virus was readily transmitted either by mechanical inoculation or by aphids, Myzus persicae and Hyperomyzus sp. It infected plants belonging to three of the eight families tested, including lettuce, zinnia, aster, Chenopodium album, C. anthelminticum, and Gomphrena globosa. The last three plants developed only local lesions. Cucumber, tobacco, tomato, petunia, bean, broad bean, cowpea, turnip, corn, etc., were not infected. 4) The virus was found to be carried over in the seed of lettuce. Seed-borne infection occured at a rate of 1 to 6per cent, in varieties Imperial 847, Great Lakes, and Wayahead. 5) The virus activity was lost when juice of diseased lettuce was diluted 1:500, when exposed to 60°C for 10 minutes, or when subjected to aging in vitro for 2 days. 6) From these results, it has been concluded that this virus is to be identified with the lettuce mosaic virus (Marmor lactucae), known from U. S. A. and other countries.
The diagnosis of the trunk blight fungus of Xanthoxylum piperitum, Nectria elegans Yamamoto et Maeda, is as follows. Perithecia caespitose, superficial, astromate or hardly stromate, ovoid, apex papillate, minutely ostiolate, outer wall irregularly warted, brightly reddish orange to red, 180∼300μ diam., 280∼390μ heigh, perithecial wall 40∼50μ wide; asci clavate-cylindrical, apex obtuse or rounded, pedicellate, 8-spored, 80∼106×8∼11μ; ascospores ellipsoid, ends rounded, one-septate, smooth, hyaline, 9∼14×4.5∼6.5μ. Conidial stage, Fusarium elegans Yamamoto et Maeda, macroconidia on sporodochia falcate, slightly curved, apex subacute, pedicellate, 1-6-septate, mostly 3-5-septate, 16∼75×3∼5.5μ, mostly 29∼63×3.5∼5.5μ; microconidia in false heads, ellipsoid or subcylindrical, rarely slightly curved, continuous, rarely one-septate, hyaline, 6∼16×2.5∼5μ; chlamydospores terminal or intercalary, solitary or catenulate, 7∼11×5.5∼9.5μ; sclerotia sperse, globose to subglobose, cyano-black, 60∼125×50∼120μ. The diagnosis of the saprogenous fungus on rotting potatoes, Nectriopsis solani (Rke. et Berth.) Booth=Hypomyces solani Rke. et Berth., is as follows. Perithecia gregarious, globose to subglobose, with a conical beak fringed with a short collar of hyphal tips, dark red, smooth-walled, 270∼400μ diam., perithecial wall 30∼36μ wide; asci clavate, apex rounded, 8-spored, 80∼98×10∼12μ; ascospores ellipsoid, one-septate, verrucose, light brown, 14∼17×7∼10μ. Conidial stage, Fusarium cuneiforme Sherb., macroconidia fusoid, sometimes pedicellate, 3-septate, hyaline, 24∼35×5∼8μ; microconidia absent; chlamydospores terminal or intercalary, solitary or catenulate, globose, thick-walled, 10∼12μ diam. Nectria elegans Yamamoto et Maeda and Nectriopsis solani (Rke. et Berth.) Booth mentioned above are different from each other in morphological characteristic as well as parasitism, which indicates that they are distinct species. However, the former fungus was mistakenly identified by Sakurai and Matuo as Hypomyces solani Rke. et Berth. emend Snyder et Hansen, and also named erroneously Hypomyces solani f. xanthoxyli Sakurai et Matuo (Fusarium solani f. xanthoxyli Sakurai et Matuo) by its pathogenicity.
As has been previously reported, the dwarf disease of mulberry tree could not be transmitted when diseased scions were grafted on healthy stocks, (moreover, the diseased scions were found to recover), but it was transmitted when healthy scions were crown grafted on diseased stocks. It was attempted to obtain further information on the nature of recovery of the diseased scions mentioned above. When diseased cuttings were obtained during a period from September to November and grown September to December, they all developed shoots showing typical symptoms, whereas the coresponding diseased cuttings grown in January showed a tendency to recover; those grown in February to May nearly or completely recovered, producing new healthy shoots. Cuttings obtained in January and February also developed healthy shoots when they were grown in February and April, while diseased cuttings which were cut and grown in May after they had shown symptoms, all produced diseased shoots. It is suggested that the virus of this disease is either inactivated or decreased in the affected shoots during winter.