1. In order to gain information as to how the change of characters due to the doubing of chromosomes differs in rate with the variety, tetraploid strains induced from 74 different varieties of Eastern Asia were grown in a paddy field from the 2nd to the 9th generations, and various morphological and physiological characters were measured.
2. Fertility varied from ca. 1% to 55% (in the average of 3 years) among tetraploid varieties, and varieties having high fertilities were relatively large in number in “Continental” variety group. The percentage of good pollen varied from ca. 55% to 95% among varieties. It was always higher than seed fertility, but was found to correlate with the latter.
3. The lengths of stoma cell in both diploid and tetraploid, as well as its 4
x/2
x ratio were recognized to be different with the variety. The 4
x/2
x ratio varied from 1.15 to 1.50 among varieties, and varieties having small stomata in diploid tended generally to be large in the 4
x/2
x ratio. A similar tendency was found also in the length of unhulled grain.
4. Generally, the height of plant, the number of grains per ear and the number or ears per plant decrease, and the lengths of ear and awn increase with the doubling of chromosomes. The 4
x/2
x ratios in the height of plant, the length of ear and the number of grains per ear were found to correlate with one another, but no significant correlation was found between these and the 4
x/2
x ratio in stoma cell length, nor between these and fertility.
5. The response to day-length seemed to remain unchanged after the doubling of chromosomes. While in tetraploid varieties the date of heading was approximately the same as the date in corresponding diploid varieties, the difference between tetraploid and diploid in heading date was a character peculiar to the variety, and varied from -4 days (4
x is 4 days earlier than 2
x) to 12 days. In tetraploid, further, heading was incomplete generally, and the distance between the neck of ear and the node (the joint of leafsheath and leaf blade) of the uppermost leaf was found to be different with the variety.
6. Germinating capacity and germinating speed of seed in tetraploid varieties were generally lower than those in corresponding diploid varieties. Germinating capacity varied from 45% to 95% among varieties, and the higher the germinating speed, the higher was the germinating capacity. Continental varieties were generally high in germinating speed in tetraploid, in the same manner as in diploid, and accordingly high in germinating capacity.
7. The resistance to pottasium chlorate seemed not to be modified by the doubling of chromosomes. Low temperature resistance seemed to be unchanged or to become slightly higher. Drought resistance measured by Mimosa method became lower by the doubling of chromosomes. In anyone of these, however, varietal characteristics in diploid varieties were distinctly seen in tetraploid varieties. Intervarietal variations of these characters were similar with those found in diploid.
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