Promotion of Lateral Female Strobili Production in Pinus densiflora by Cytokinin Application at a Specific Stage

Abstract

BAP (N 6-benzylaminopurine) was sprayed 5, 10 and 15 times at four different periods to promote flowering of a grafted Japanese red pine (Pinus densiflora) clone. Four stages were I, August 4 to September 1; II, September 6 to October 4; III, October 5 to November 14 and IV, November 30 to December 28, in 1994. Concentration of BAP was 250 mg/l. In May, 1995, no apical female strobili were observed at the top of the new shoots in any treatment. However, BAP application at stage III (floral differentiation period) produced lateral female and bisexual strobili at the lower part of new shoots. The numbers of lateral female and bisexual strobili were 87 out of 147 to 234 out of 162 new shoots. Frequency of BAP application did not affect the numbers. Marked decrease in number of male strobili induced by BAP application at stages I and II was observed. In contrast, the number of new shoots was increased by the BAP application at the above stages. Treatment at stage III and IV did not affect significantly the number of male strobili and new shoots. These results indicate that BAP application at stage III specifically induces the development of lateral female and bisexual strobili in Japanese red pine.