Physiological Studies on a Wilt Resistant Strain of Flax with Special Reference to the Effect of Soil Condition

[摘要] The flax wilt disease caused by Fusarium lini, gives the most destructive injury to the crop and it has been proved that a certain crop-rotation for long interval, to be only the effective method for the prevention of its occurrence. But the breeding of some resistant strains to the disease should be the most desirable thing in the flax cropping. Since 1902, under the direction of Professor MINAMI, the successive cropping experiment of flax has been made at the experimental field of the Hokkaido Imperial University, and in the course of that experiment an excellent flax strain being resistant to the wilt disease was bred true from Riga variety. The present paper reports the nature of the resistant strain (marked MR in thjs work) comparing with the original Riga variety (marked 0R) from a physiological standpoint. The experiments were carried out in two series to prove the influences of the soil moisture in one series and the influences of the soil temperature in the other upon the occurrence of the wilt disease. The materials were grown principally on thc sick soil which was taken from the field, where the successive cropping experiment has been carried on. Firstly, in order to control the soil moisture of each pot, the writer used the LIVINGSTON's auto-irrigator, regulating its mercury column in height of O, 1, 3, 4 or 7.5 cm., in which the percentage of soil moisture was actually found to be 55.1, 55.0, 47.0, 43.0 or 35.8 respectively. Secondly, an experiment was carried out to ascertain the influence of soil temperature ranging from 15° to 40°C, Each plot was controlled approximately at intervals of 5°C, The results of these experiments are summarized as follows: 1. In relation to the difference of the soil moisture content, OR and MR showed generally a marked difference in susceptibility to the wilt disease; OR wilted more severely in low soil moisture (35.8%) showing about 68% of wilted plants, while in higher moisture content (55%) the percentage of the occurrence of the wilt was about 42%. On the contrary, in the same condition, MR showed the percentages of wilted plants ranging from 0 to 2.1%. As this set of experiment was carried out in the green-house, the soil temperature fluctuated between 15°--22°C, which is not a very favorable condition for the occurrence of the wilt disease. 2. Results of the experiment in regard to the control of soil temperature are summarized in the following table: Percentages of wilted individuals on the 20th days after germination at various soil temperatures (The moisture content of soil was uniformly kept at ca. 44%) [table] 3. From the above result, it will be understood that: (a) At the temperature below 30°C, OR shows higher susceptibility than MR. (b) In the case of OR, the optimum temperature for the occurrence of the wilt disease ranges from 25°C to 30°C, while in MR it is 30°C or a little higher. (c) Above 30°C OR shows higher resistance than MR. 4. To learn the protoplasmic difference between two strains, epidermal or subepidermal cells of hypocotyle were compared by means of plasmolysis. As plasmolytica 0.3-0.5 mol. sugar solutions were used. It was very interesting to note that MR showed a higher percentage of " Krampfplasmolyse " than OR. 5. The protoplasmic character (Krampfplasmolyse) of MR was compared with those of other 12 varieties of flax, and MR showed excessively high percentage of " Krampfplasmolyse " among all of them. 6. It was noticed that the appearance of these two kinds of plasmolysis varied in accordance with the change of the soil temperature, and it seems also to have some relation with the change of the percentage of the wilt disease. 7. From the above results it is considered that the physiological character of the protoplasm may have a certain relation with resistance of this MR strain.

[学科分类] 农业科学（综合）