In order to clarify the mechanism of histological barriers to pathogens of witches’ broom diseased in sweet potatoes, this experiment has been conducted to observe the relationship between pathological characters and the transfer of mycoplasmae in the shoot apex. The material used the experiment is the sweet potato (Ipomoea bat at as (L.) Lamm. Suwon 147).
In the experiment regarding of mycoplasmae, the upper limit zone of transfer of mycoplasmae is examined by way of the process of free stock and the shoot apex of a infected part in nature, observed in the culture of each part of the diseased plant which is cut to a certain length. The pathological change pattern of tissues infected with mycoplasmae has been observed under the light and electron microscopes.
As a result of this experiment, the following conclusion was arrived at.
1. It has been ascertained that the mycoplasmae are not existent in a promeristem and primary meristem zone from the meristem dome; and is existent in the lower-part-of the vascular- differentiation zone, after which differential tissues the mycoplasmae become progressively enlarged, and before which undifferential tissues it become progressively immature and diminished in size.
2. It can be suggested that mycoplasmae may not be existed in the shoot meristem, because the passing structures such as sieve area and plasmodesma which can be passed immatured-mycoplasmae is undifferentiated.
3. In the tissue culture, free stock can be obtained in the zone between 1.0-1.5mm of the shoot apex, while it cannot in the 2.0-3.0mm zone, because of infection by mycoplasmae. It is suggested that immature mycoplasmae may be diffused according to temperature(28±1℃) in tissue culture process.
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