The effect of several plant growth regulators was investigated by removing floral head of Tulipa gesneriana L. cvs. Jacqueline and Red Matador. The influence on the flower stalk elongation by elimination of their floral parts and leaves also was investigated, The results were summarized as follows;
For the effect on the concentration of NAA, there were differences between cultivars. For cv. Jacqueline, the elongation of third internode and neck (last internode right below the flower head) were promoted with 1.0mM or 2.0mM and 1.0m1VI in case of cv, Red Mlatador. After the treatment with GA₃, for cv. Red Matador, only the first internode growth was stimulated slightly, yet there was no effect on the neck growth. The elongation of the first, second internodes of cv. Jacqueline was slightly promoted at 1.0mM of BA. However, there was no such effect on the third internode and neck growth by BA treatment at 1.0mM. As far as NAA effect was concerned with neck growth, it was promoted with NAA for 14 days after treatment in cv, Jacqueline, but NAA＋GA₃ treatment showed less striking effect than b NAA treatment, The early growth rate of cv. Red Matador by NAA treatment was less extensive. After treating with IBA, for evs. Jacqueline and Red Matador, the third internode and neck growth were more markedly increased than by NAA treatment. In comparison with GA₃ or GA_(4＋7) treatments, the latter made the neck growth greater than the former for both cultivars. It, however, showed a peculiar phenomenon that the neck growth took place 1das after the treatment of GA_(4＋7). The neck was quite extensively elongated by NAA treatment at a both the visible flower-bud stage and 5 days after it in cv. Jacqueline, whereas the elongation was reduced at the time of 10 days after the visible bud stage. For cv. Red Matador, the length of elongated region was shorter than of cv. Jacqueline, but the growth pattern was very much alike, The neck growth of both cultivars with NAA＋GA₃ treatment was somewhat reduced in 5 and 10 days after the visible bud stage. For cv. Jacqueline treated with NAA＋ BA, the third internode and neck growth were more promoted 5 days after than the visible bud stage. For cv. Red Matador, there was no such characteristic on the growth. The neck growth of cv, Jacqueline was promoted by NAA＋GA₃＋BA treatment 5 days after the visible bud stage.
The third internode and neck growth were notably inhibited by removal of floral head of tulip, and this was reversely increased considerably by NAA treatment. The neck growth inhibited by ancymidol, PP333 and ABA treatments was recovered by NAA-supplemented mixture of treatment for the same concentration. Especially the third internode and neck growth inhibited by TIBA treatment were recovered completely by TIBA＋NAA combined treatment, and it increased the growth more than NAA alone. Growth of neck, and the first, and third were inhibited by removing gynoecium and perianth.
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