Abstract
1. The sclerotial or Botrytis rots of onions are found very often upon the stored bulbs in the central markets, as well as in the shops of greengrocers in Kyoto and Osaka. In the previous paper, the writers described the gray-mold neck rot caused by Botrytis Allii MUNN, which is most common and causes heaviest losses among them, with special reference to the morphology and the pathogenicity. of its causal fungus.
2. In the present paper, the mycelial neck rot caused by Botrytis byssoidea WALKER, the small sclerotial neck rot caused by Botrytis squamosa WALKER and. also a new disease caused by an undetermined species of Botrytis were described in detail.
3. Although the occurrence of these three diseases seems to be very rare in this country, they have been produced repeatedly by inoculating onion bulbs through needle wounds with mycelium from pure culture and with conidia and conidiophores which developed upon infected bulbs, upon the potato-dextrose agar or upon the sclerotia placed on the sterilized soil in the case of the hitherto undescribed disease.
4. The symptoms of these diseases, as well as the morphology of their causal fungi were first described. The results of the cultural experiments carried out by the writers were then given in detail.
5. It was demonstrated clearly by carefully inoculating the outer succulent scale of a bulb that the most satisfactory method of obtaining infection by B. byssoidea was of course to inject conidia into needle wounds, placing bulbs under conditions in which toorapid desiccation of the wounds is prevented. Under humid conditions and favorable temperature, invasion of the unwounded outer succulent scales has been scarcely noted in a slight degree.
6. A number of experiments were made to determine the relation of temperature to infection by B. byssoidea and the rate of progress of decay. The results show that infection seems to occur in a wide range of temperature ranging from 3°C to 32°C, although the most rapid decay takes place at temperatures from 10°C to 24°C.
7. Even at the most favorable conditions, the decay of onion bulbs caused by B. squamosa progressed much more slowly than in the case of other three species of Botrytis isolated from decaying onions.
8. Many inoculation experiments with the undetermined species associated with onion rot were also performed by the writers. The results show that its pathogenicity seems to be as strong as to penetrate at times the unbroken cuticle of succulent scales. The most favorable temperature for the decay caused by this fungus seems to lie at approximately 24°C.
9. All four species of Botrytis associated with onion rot differeach other not only in their spore-dimension, but also in their cultural characteristics especially on the plate of potato-decoction agar containing 2% dextrose.
10. Inoculation experiments performed by the writers demonstrated clearly, that all the strains of Botrytis cinerea PERS. isolated from decaying fruits of strawberry and Satsuma-orange, and also from lettuce have power to infect the succulent scales of stored onions, when injected conidia together with conidiophores into needle wounds.
