Studies on bolting in Brassica

VI. Influence of the genetic factor on internode elongation

Abstract

Several varieties of different ecotypes were used as materials. The seeds of each varieties were sown in pot on February 15, May 18, July 20, September 15 and December 2 in 1968.
The effect of sowing time, temperature, humidity and light intensity on internode elongation was observed.
The elongation of hypocotyl, epicotyl and other internode was observed at leaf stages 2, 4, 6, 8 and 10. The results were as follows:
The internode elongation was accelerated by high temperature, and low light intensity. Humidity has no effect on elongation of internode. Internode elongation was also affected by genetic factor. In this report, especially, genetic factor is emphasized. The distinct difference was recognized in different genome varieties at early stage. Namely, in A-genome varieties, hypocotyl was elongated by several environmental factors, but epicotyl and other internodes did not elongate except after vernalization. In B-genome varieties, epicotyl and other internodes elongated every sowing time. In C-genome varieties, 4 or 5 internodes were elongated before the 8th leaf stage, and afterwards the plants appeared rosettes. But, when the period of vegetative growth was prolonged, distinct elongation of the lower part of the stem occurred. Takana and Karashina groups were used as AB-genome varieties. Internode elongation of Karashina group is similar to B-genome varieties and Takana group resemble A-genome varieties. AC-genome varieties were constituted several types, some of which are similar to A-genome type and the others (for example, Rutabaga) resemble C-genome type. The other types of AC-genome varieties were distributed between the above two groups concerning the internode elongation. It was also recognized that if the vegetative growth was prolonged, the lower part of the stem was elongated. It resembled the C-geneme varieties.
Although the elongation of the lower part of the stem was observed in C- and AC-genome varieties, the length in AC-genome varieties was shorter than in C-genome varieties. As the elongation phenomenon of lower part of stem was not observed in A-genome varieties, it was considered that AC-genome varieties had the intermediate character of A- and C-genome varieties as regards the length of lower part of stem.
The distinct difference was also recognized in scape elongation at low temperature. At 5 to 15°C, scape elongation of A-genome varieties was inhibited completely. Scape elongation of C-genome varieties, on the contrary, was formed normal.