1. This paper gives the results of studies on the symptoms of the sclerotial disease of narcissus, and the morphorogical and physiological characters of the causal fungus.
2. The symptom of the diseased narcissus appears at first as yellowing of the tips of leaf blades which gradually spreads to whole plant with the appearance of very small sclerotia on the outer skin of bulb. If the infected bulb is planted in the following year, it shows a very poor growth of premature yellowing of the leaf blades. The bulb finally contracts by drying and dies.
3. The sclerotia of the fungus are spherical or subspherical in shape, black or dark brown in color, and measure 80-70×165-121μ in diameter on the host. The microconidia are spherical, smooth and measure about 2.0-2.5μ in diameter. Apothecia are not produced.
4. The cultural characters of the fungus were studied on ten different media. It was found that potato, bean, SAITO's soy onion, and CZAPEK'S agars were suitable for the mycelial growth; while potato, bean, CZAPEK'S, RICHARD's, and apricot agars at 20°C. for the formation of sclerotia.
5. The relation of temperature to the growth of the fungus was studied on ten different media. It was found that the optimum temperature for mycelial growth was 28°C., the minimum below 0°C, and the maximum between 32° and 36°C.
6. The relation of hydrogen-ion concentration to the mycelial growth was studied on potato agar. The growth occurred in media ranging from pH 1.9 to 10.1, and the pH 4.8 was observed to be most favorable. Sclerotia were produced at every concentrations, but were produced later at high and low ends of the pH and fewer in number at high concentrations.
7. The relation of sucrose concentration to the mycelial growth was studied on potato agar medium. The best concentrations were between 5 and 7%, but fair growth was observed even at 30%. In both high and low concentrations, there was a tendency for the growth of the fungus to decrease rapidly. Sclerotia were produced abundantly only on non-sucrose medium, and as the sucrose concentration increases, it interfered with the formation. When the concentration reached 7% or more no sclerotia were formed.
8. The relation of NaCl to the mycelial growth was studied on onion agar. The most favorable growth was noted on the medium in which no salt was added. An increase in salt concentration interfered with the growth. It was entirely stopped at 8% concentration. The sclerotia were formed only on the saltless medium.
9. Narcissus, tulip and onion bulb, gladiolus corm can be infected artiicially by inoculating them with the fungus mycelium. The disease is specially manifested when the fungus is introduced into the soil.
10. The viability of the causal fungus was observed to be about two years in test tubes.
11. According to my study, there are 12 varieties of narcissus that can be infected with the disease.
12. In connection with the import plant inspection work, this fungus was first noticed at Yokohama port in 1928 on the diseased tulip bulbs imported Crom Holland, and ever since, it has been intercepted at various parts of Japan proper.
13. This causal fungus is identical with
Sclerotinia gladioli (MASS.) DRAVIDSON, causing the dry rot of gladiolus.
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