Author: T. C. Fang, B. Y. Jiang and J. J. Li
J Integr Plant Biol 1962, 10 (4): -.
The present paper deals statistically with the causes of variation in the stipe length of haidai, Laminaria japonica (Fig. 1); currently cultivated commercially in China, and with the mechanism of the appearance of the long stipe character in a new breed named Haiqing No. 1 of haidai, which has appeared recently by selection. A study has been made on the average stipe length of three different populations of haidai cultivated under almost similar conditions in Tuangtao Bay at Tsingtao. The so-called "natural" population was taken from the cultivation industry, and is a population arising from crossing of many gametophytes grown from the spores of mature sporophytes. It may be taken to represent the present commercial haidai populations cultivated at Tsingtao. The differences in stipe length in the three populations given in Table 1, when tested by using the formula, are statistically significant. The difference in the stipe length of the “natural” and inbred populations is considered to be partly due to the different growth densities and consequently different amounts of light received, since in the “natural” population more than 40 sporophytes: were fastened to a small palm rope with a length of 1.5 meters, while in the other two. populations only 10–15 sporophytes were fastened to a similar small palm rope with a length of 0.3 meter. The sporophytes were all grown in the 1 meter layer below sea surface. However, the difference in growth density cannot explain all the differences in the three populations, for although the Haiqing No. 1 breed and the inbred population were cultivated under similar growth conditions, the former has very much longer stipe. Cultivating gametophytes under high temperature (20 ℃ or 22℃) seems to have some effects on the stipe growth, however no definite variation has been observed (Table 2). What effect high temperature has on the subsequent growth in length on the: stipe needs further studies. The average length of stipe of the populations from autumn and summer sporelings was quite similar, and no significant difference in the four populations has been Observed (Table 3). Since the autumn sporelings were from parents; that had undergone several months of high' temperature, different temperature conditions under which the sporophytes lived apparently have little effect on the stipe length of their offspring. On the other hand, a study of the stipe length of the parent sporophytes and that of their offspring showed a close correlation of stipe length between parents and offsprings, an indication of inheritance of the character under consideration~ (Table 4). Similar results have been obtained with the stipe length between the parent and the offspring in the new breed Haiqing No. 1. Thus, the same parent with stipe length of 6.0 cm. gives four groups of offsprings all with similar average stipe length of from 5.9 cm. to 6.9 cm. (Table 5). This also supports the hypothesis that stipe lengtl of haidai is an inheritable character. It should be noted that the data from the experiments conducted at Amoy do not support Parke's view that stipe grows shorter in the south. A discussion on the origin of the genetic basis of stipe length has also been made. We are of the opinion that the character of long stipe in the new breed did not arise- from directed variation due to high temperature treatment applied to the gametophytes, nor from induced mutation, but has rather come from the segregation and recombination of genetic factors in the hybrid parent through the interaction of selection and in- breeding. From the different frequency distributions of stipe 1.ength in different pedigrees (Table 6 and Fig. 2), We can clearly see a genetic process of segregation from a hybrid parent population into short and long stipe populations, and the gradual appearance of long stipe population. It is suspected that a number of genetic factors is involved in the stipe growth character.