| 3. Requirement of vernalization In the next experiment, the periods requiring for the full vernalization were examined. The seedlings of alloplasmic lines of Chinese Spring and three indicator strains were treated with low temperature (8C) under continuous illumination (about 2,000 lux) for the different periods ranging from 10 to 50 days. After the treatment, plants were transfered into the growth chamber (Koitotron KG-106 HL-D type), which was controled with the luminous intesity of 28,000 lux for 17 hours (20C) and about 10,000 lux for 7 houres (18C) a days. In each plot, ten individuals were planted in a dense space (5 cm x 3 cm). Table 5 shows the average days until the flag leaf emergence after the end of the treatment of low temperature. According to the experiment by GOTOH (1976), the completion of vernalization is achieved when the days until flag leaf emergence become less than 34 days under the condition of continuous illumination with high temperature, after the treatment of low temperature. Based on this criterion, Chinese Spring and three alloplasmic lines of Chinese Spring with Ae. squarrosa, Ae. umbellulata and Ae. vavilovii cytoplasm required the vernalization for 10 days, in which category the indicator Shirasagi (grade III) was included. While (ovata)-Chinese Spring required the vernalization for 50 days to achieve the criterion, even the indicators Aoba (grade IV) and Nambu (grade V) achieved the criterion by vernalization for 25 days and 30 days, respectively. This result alone might lead to conclude that (ovata)-Chinese Spring have stronger winter habit than that of Aoba or Nambu. However, since (ovata)-Chinese Spring headed later by 11 days than the control Chinese Spring in the field experiment at Kurashiki where the full vernalization must have been achieved during winter, it is concluded that the vegitative growth period was extended by 11 days by the introduction of Ae. ovata cytoplasm in Chinese Spring. Considering the extension of vegitative growth period, it is estimated that about 45 days until the flag leaf emergence could be the criterion to achieve the full vernalization in case of (ovata)- Chinese Spring at the experiment in the growth chamber. Then, (ovata)-Chinese Spring required the treatment of low temperature for 25 days to achieved the criterion of full vernalization, which is equivalent to the indicator Aoba (grade IV). Consequently, it can be concluded that the degree of vernalization requirement of Chinese Spring is altered by the effect of Ae. ovata cytoplasm from grade III (weak spring habit) to grade IV (weak winter habit). The results of the present experiments suggest that the interaction between the plasmon of Ae. ovata cytoplasm and the plasmon-sensitive gene or genes in T. aestivum cv. Chinese Spring is responsible for not only the extention of vegetative growth but also the alteration of growth habit from spring habit to winter habit. |
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