1923 年 1 巻 5 号 p. 13-19
Since 1913, an undescribed bacterial leaf spots of Hibiscus has been under observation in Korea. The most noticeable lesions in leaves are found as irregular black spots which cause the distortion of the leaves. The causal bacteria have been isolated repeatedly and its pathogenicity proved by inoculation with pure culture. The disease is briefly described as follows:
The disease affects the cotyledons, especially young leaves when 2-3 leaves are expanded, but reduced when the plants matured. The first signs of the disease are minute circular black spots which enlarge in size gradually and take circular or irregular outlines, then finally the margins become angular limited by the veins. The outer parts of the spots take on obscure whitish yellow colour or water soaked appearance, and when the leaves are severely attacked the whole plants become blackend and dry out.
Description of causal organism:
Bacterium Hibisci, n. sp.
A cylindrical rod with rounded ends, single or pairs usually and chains frequently, 1.2-2. O X 0.6-0.7 μ. in size, motile by means of 1-2 polar flagella, no spore or capsule formed, Grams-negative, and stains well in carbol fuchsin, anilin water gentianviolet, and aqueous methylenblue; in agar plate, the surface colonies are smooth and circular with entire margin, slightly elevated in center, wet shiny and cement-like coloured by reflected light, fine granular in center under magnification; bouillon culture clouded after 20 hours at 25-27°C, and rim produced with heavey precipitate; gelatin slightly lignified, milk slowly peptonized, no gas produced, nitrate slightly reduced, no reaction of indol, thermal death point at 49°C, aerobic. Infection experiments
Inoculation by needl puncture with water suspension of 24 hours agar culture resulted characteristic leaf spots but inoculation by spraying failed to give infections. When the seeds soaked with water suspension of agar pure culture are sowed, the germinated young plants showed lesions of bacterial blight on the cotyledons.
Our experiment shows that this organism overwinters on seed. In April 1921, the seeds were disinfected for 10 minutes with mercuric chloride (One to 1000 part of water) or hot water treatment (55°C) and then sowed in large tube with sterilized sand. The plants germinated, grew soundly and no disease was observed, but the plants from untreated seeds showed 50 per cent diseased leaves.
Our experiments for control during the season of 1919 and 1920 show that the seed disinfection is very effective, application of 5-5-50 bordeaux mixture spray greatly reducing the disease.