Evidences have been confirmed concerning climatic conditions in relation to the severeness of black rot of sweet potatoes in fields. The data were obtained from the variety experiment at Shirai-mura near Chiba from 1941 to 1948. The basal portion of inoculated slips healed not infrequently after planting, though they used to be attacked there. The healing was distinguished in the year with the highest mean temperature being at about 30°C for 10-day-period. The temperature observations were taken at 10 o'clock. The higher in the temperature the more remarkable is this phenomenon (Fig. 1). This is referred to as the effect of a curing as such mentioned by YOSHII (1945). The varietal difference of the infection of the roots has a tendency to be correlated with the injury by wire worm, Melanotus caudex LEWIS. Similar tendency is acertained in regard to the yearly deviation on the same varieties (Fig. 2). The number of the pits was in inverse proportion to the precipitation at the first 10-day period of March (Fig. 3). In this case the correlation coefficient reaches to -0.89 and is highly significant. At about this period, the wire worm in that field is surmised to move upward from deep to just beneath the surface of soil, and subject to the effect of precipitation. Deviation of the dots Nos. 16 and 17 in Fig. 3 is explained by the earlier upward movement resulted by warmer winter (Fig. 4) and larger precipitation of the preceding 10-day period in the year Showa 16 (1941), and by the delayed upward movement caused by colder spring (Fig. 4) and meagre precipitation of succeeding two 10-day periods in the year Showa 17 (1942). The number of the pits may be presumably in proportion to the number of the worm itself. The precipitation of the first 10-day period of March has a curvilio, near relation to the percentage of the diseased roots (Fig. 5), similar to that between the latter and the index of the wire-worm pits. The length of the lesion at the basal portion of the slips correlates with (1) the mean temperature for the last two 10-day periods of August (Fig. 6). Correlation coefficient reaches to 0.92 and is highly significant. (2) the mean temperature for the growing season of sweetpotato, (3) the mean temperature for September and October, and (4) the mean of maximum temperature for the first two 10-day periods of September also suggest tendencies of positive correlation to the enlargement of the lesion, though it is not significant. As a whole, the higher the temperature in August or thereafter, thel arger is the development of the diseased part at the base of the stem. This is apparently in contradiction to the result on the healing mentioned first. However, the curve B in the figure 6 suggests a rather suppressive effect of high temperature in 1948 (22 in the figure). The distribution of the dots in fiure 7 is suggestive of a certain influence of concentration of the pathogen on the outbreak of this disease in the field, since the meagre outbreak of the disease in 1941 (16 in the figure) cannot be explained otherwise, i. e. the lower temperature in summer and autumn might prevent the increase of the pathogen, in spite of the worm pits were rather numerous in this year.
The cut surfaces of sweet potatoes were subjected to various treatments and inoculated with Rhizopus nigricans EHRB. After 10 days' storage, notes were taken of the soft-rotten potatoes. The results show that wounded potatoes were liable to soft rot. The percentage of rot was particularly high when the cut surface of the potatoes is treated with alcohol, exposed in the sun, or injured by contusion. The reason for the susceptibility of these potatoes may be attributed to the reduction of physiological vigor and delay of wound periderm formation in the tissue beneath the cut surface. It will be seen from the results graphed in Fig. 1. that there was less rot of potatoes placed in a moist chamber before or after inoculation than the potatoes placed in a dry chamber. In a higher humidity, the tissue of cut surface would be expected to be vigorous, and the suberization proceeds more rapidly.
1. As has been reported in the previous paper, the ability of B. solanacearum of utilizing carbohydrates in synthetic media is variable accoding to the kinds of the food material used as a nitrogen source; namely, in the presence of nitrates the organism produces acid and gas from dextrose, saccharose, etc., while in the case of ammonium salts only an acid reaction is noticed. This fermenting ability can therefore be employed as a means of distinguishing the strains. In Formosa there are at least 4 strains, one of which is the tomato strain and the others are tobacco strains. The former is considered to be identical with the SMITH's orginal type and the latter may be the strains derived from the former. These strains can be differentiated by the fermenting ability of dextrose, lactose and mannit, provided that 0.1 per cent solution of K2HPO4 and NH4NO3 plus agar was used as a basic medium and brom thymol blue as pH indicator. 2. Among the first-named three strains, morphological differences were noticed in the size of individual cells, number of flagella and staining reactions. but under the microscope these were not sufficiently distinct to separate them from one another. In milk cultures the tomato strain clears the milk, shifting the reaction to an alkaline side, while the tobacco strains coagulate the casein by the formation of acid. 3. It is confirmed by a number of isolations made from the diseased tomato and tobacco plants that there exist some relationships between the strains and host plants. The tomato strain is usually highly infectious to tomato plants, though it is also parasitic on tobacco, producing a mild symptom usually confined to the one side of the plant, when they are attacked at a young stage under the moist, hot weather conditions. On the other hand, the tobacco strains are not only virulent to tobacco, but also sometimes attack tomato plants to such an extent as giving the symptoms hardly distinguishable from those produced by the tomato strain. It is noticed, however, that the tomato strain, if allowed to take the long-continued in vivo life on tobaccoes by means of the successive passages or to remain long on the same host without. transfer, was able to change into the tobacco strain-I which is capable of producing the acuteform symptoms on tobacco plants. The tobacco strain II appears to have a character of losing virulence which is acquired by the continuous association with tomatoes. 4. In the previous paper, the writer reported on the relationship between the diphasic symptoms and colony variants, but the results of the present studies conducted by means of rootinoculation revealed no evidence to support it, because the colony variants, C and Op types, which were considered as a cause of mild-type symptom in the field have little abilities to cause a wilt disease, and if they could, the symptoms were very mild, only restricted to some lower leaves which are characterized by a yellowish local withering or blackening of the veins, and not extended to the whole plants. The symptoms of tomatoes affected by the tomato strain are either the mild or the severe types depending upon the condition of the host and weather, while the tobacco strain-I usually gives the severe-type symtoms on tobaccoes, and the strain-II gives the mild one. The latter, however, is able to produce the severe type if the plants is young and succulent, and the weather is hot and humid. It is further noticed that any strains tend to produce the mild-type symptoms after having decreased their virulence. The writer is inclined to believe that the diphasic symptoms may be partly due to the conditions of the host and temperature.
This paper reports “Ear-blight”, a nematode disease of Italian-millet (Setaria italica). The symptoms were found to be identical with the description given by NAKANO, who reported that the parasite probably belonged to Tylenchus (Anguillulina). With their studies on the morphology of the pathogenic nematode, the writers came to the conclusion that the pathogen is identical with Aphelenchoides oryzae YOKOO, the causal organism of white-tip of rice. (Laboratory of Plant Pathology, Kyushu University)
(1) The antifungal substance produced by a Cephalothecium sp. has been isolated in crystalline form and the name “Cephalothecin” is proposed for it. (2) The best yields of the Cephalothecin have been obtained by culturing the Cephalothecium fungus in a modified RICHARDS medium (KNO3 5g, MgSO4 1.25g, KH2PO4 2.5g and Sucrose 25g in distilled water 1l, and added with corn steep liquor 5 cc. pH is adjusted to 5.5. (3) Cephalothecin contains neither halogens, sulphur, nitrogen nor phosphor. It is readily soluble in alchhol, acetone ether and chloroform, but only slightly soluble in water. Aqueous solutions of Cephalothecin tolerated against heating one hour at 100°C. without any loss of activity.