Japanese Journal of Phytopathology

The cause of white rot of hyacinth is a bacterial pathogene different from WAKKER'S yellow rot organism. The organism is able to attack many other raw vegetables. In morphological and physiological characters it is to be identified with Bac. aroideae.

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1. On inoculating eight kinds of cruciferous plants with the conidia of Peronospora Brassicae GÄUM. the germ tube was seen to penetrate the epidermis always through the boundary of two epidermal cells. Entry through the stomata, as reported by IKATA & YAMAUTI (1931) and others, was not ascertained.
2. In a moist chamber of about 15°C the conidia placed on the leaf of the host germinate in four to six hours. Appressoria are formed in twelve hours and infection hyplhae in 18 to 24 hours.
3. The infection hypae send out haustoria into the epidermal cells, or first into the internal cells when they have reached the intercellular space.
4. On the leaves of the host a characteristic symptom appears at about 15°C two days after inoculation, followed by the formation of the conidiophores and conidia one to two days later.
5 On the cut surface of the turuip- and radish-root inoculated with conidia at about 15°C, the fungus develops rapidly and forms conidia luxuriantly in four to six days.
6. The form of haustoria in the root of turnip and radish is variable. At first they are spherical or pyriform, and later they assume a cylindrical or club-shaped form. Often they are divided into two, three or more branches. The largest unbranched. haustorium measures 108μ in length and 25μ in width.
7. In general the haustoria developed in the leaf are much smaller, the largest being 11×8μ in dimension. Usually they are spherical, often divided into two or three lobes. The haustoria formed in the stem of Brassica chinensis are cylindrical or club-shaped, being sometimes dichotomous. The largest one measures 57×14μ.
8. Around some haustoria the so-called sheath can be distinclty recognized. The relative length of the sheath to that of the full-grown haustorium is variable, some appearing as a collar round the neck and some attaining one third or one half length of the haustorium. It is probable that the haustorium at a young stage is enclosed in the sheath, but during its growth the sheath would finally be broken. However, it is not always the case, for we find some full-grown haustoria which remain enclosed in the sheath. It is likely that they ore functionless.
9. Ensheathed haustoria are very frequently found when a vigorous or fresh root is inoculated, but they are rare in the tissue of the root which becomes old or less vigorous.

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