Lammas shoot induction in Pinus densiflora by heating in spring

Abstract

The potted, two-year-old seedlings of Pinus densiflora were transferred into a greenhouse from the outdoors on February 20, March 7, and 22, 1990, before the initiation of spring flush. On May 22, 1990, the plants were returned to the outdoors. The earlier the seedlings were transferred into the greenhouse, the earlier the second flush started, the greater the percentages of Lammas shoot elongation were, and the larger the amounts of the secondary flush were. In the second experiments, potted seedlings were divided into two groups: 1) 139 plants grown in the greenhouse from March 6 to June 4, 1990 (heated), and 2) 237 plants grown under outdoor conditions (non-heated). The terminal buds of the seedlings in both treatments were periodically sampled and the number of leaf primordia formed on the buds was counted with a microscope. In the heated seedlings, more than 90 leaf primordia were observed in August when rapid internodal elongation in the buds occurred. While more than 90 leaf primordia were observed in the non-heated seedlings in September under short-day conditions, the internodal elongation did not occur. It can be concluded that Lammas shoots in Pinus densiflora are the elongated buds, which have formed 90 through 100 leaf primordia under 14 h day length or more.