2026 Volume 25 Issue 2 Pages 101-107
The selection of chrysanthemum cultivars that flower stably at high temperatures will contribute to planned production during hot seasons. This study aimed to identify the external and internal factors that affect flowering of summer to autumn flowering chrysanthemum cultivars. Experiments were conducted in an open field with different temperature and day length treatments. The degree of flowering delay due to high temperatures was smaller in cultivars with greater flowering potential at high temperatures. The degree of flowering delay due to high temperatures was greater under floral-inductive, but suboptimal day-length, compared with optimal short-days. The longer the critical day length for flowering of the cultivar, the lower the degree of flowering delay due to high temperatures under natural day-length in Japanese summer. Thus, two environmental factors, temperature and day-length conditions, and two corresponding plant characteristics were shown to affect flowering. Using cultivars with greater flowering potential at high temperatures and longer critical day lengths for flowering should lead to more stable flower production.
