Studies on the so-called“ Home and Foreign”crops of seed of“ Tokinashi”radish, a Japanese spring variety.

Abstract

1. The“Foreign”seeds, collected from the strains cultivated in Oita prefecture, was much larger in size than those of the“Home”crop, which have been collected at Kyoto prefecture, so it was quite easy to discriminate each other crop from this character.2. It is a well-known fact that the“H”-seed growers in Kyoto obtain their crops by harvesting the seed at its premature stage. The author had grown, on the experiment farm, both the strains from those different sources, and compared the effect of maturing condition at the harvesting upon the size of seeds produced. The results of the experiments disclosed, however, that seeds of the Oita strain (“F”crop) has shown only a slight tendency to become smaller in sfze by the premature harvesting, making more or less clear contrast with the Kyoto strain (“H”crop), which has shown a more distinct behavior to this situation. Therefore, each strain may be duely considered as of somewhat different in this characteristic.3. Detailed measurements of the weight of individual seeds were made, and compared betwheen the“Home”and“Foreign”crops. Variability in size of the Kyoto-grown seeds was much more smaller than that of Oita ones, and both the variation polygons compiled (presented in Fig. 1) did not take a regular symmetrical arrangement, showing similar shift toward the lighter classes of seed-weight, though this tendency was rather conspicuous with the“Home”crop.4. With each strain, seeds were divided into three different categories in size, i. e., large, medium and small, and they were sown in the separate field plots on 7th, Feb. and 23rd, Feb. 1947, and their individual growth responses were examined. The Oita-grown seeds showed, in general, rather faster germination, e. g., three days ahead of the Kyoto ones, and the cotyledons of the former strain were also larger than the latter. In consequence, the difference in growth rate of young seedlings was clearly descernible between those two strains, and the quite similar situation was also encountered between the large and small grain-plots belonging to the same strain.5. The Oita strain showed rather earlier bolting tendency than the Kyoto strain, and run to seed rapidly. Bolting behavior of the former seems to be somewhat different from the latter, and thus the former is considered to be much more sensitive to the thermal induction of repro-ductive development. Therefore, under the environmental conditions prevailed during this experiments, it may be duely considered that the Oita strain had experienced the sufficient thermal induction under the spring temperatures and had run to seed. The Oita strain, in consequence, should not be sown so late in winter or earlier in spring for the root-crop production.6. In both strains, plants grown up from the larger seeds were apt to run to seed more rapidly than those from smaller ones, but, in general, the genotypic nature of the strain is considered to be much more influencial factor upon the bolting behavior of the strain.7. With these two strains, there could be noticed the different correlative relationship existing between the root growth and the bolting habit. With the Kyoto strain there was no difference in the amount of root-growth between the bolters and non-bolters, so the larger root crop of commercial size could be easily attainable before the elongation of seed-stalk. But with the Oita strain, the root-growth attained by the early-bolters did not reach to its full size, and therefore this behavior may be taken as the effect of an unfavorable character for the practical root crop culture.8. From the above results, it may be duely appreciated that the smaller size of seed of Tokinashi variety can be taken as an important criterion of the “Home”crop or strain.