Studies on the strains of Bact. solanacearum

Abstract

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.