High Temperature Effects on Growth and Floral Development of Chrysanthemum

Abstract

Abstract Pinched plants of Chrysanthemum morifolium Ramat. ‘Orange Bowl’ and ‘Surf’ grown in a chamber maintained at 22° day/18°C night were transferred to 30° day/26° night at the beginning of week 1, 3, 5, or 7 after start of photoinduction period (15-hr nyctoperiod). Plants remained at high temperatures for 2, 4, 6, 8, or 10 weeks and then were returned to the 22°/18° chamber. Exposure to high temperatures during the first 4 weeks of short days increased the number of nodes, leaf area, stem length, and dry weight of leaves and stems. Rate of floret initiation and perianth differentiation decreased when exposed to high temperatures during the first 4 weeks of short days in ‘Orange Bowl’ but not in ‘Surf’. ‘Orange Bowl’ exposed to high temperatures for 10 weeks from the start of short days flowered 12 days later than plants grown at lower temperatures and formed bracteate buds. Flowering of ‘Orange Bowl’ grown at 22718° during the first 4 weeks of short days, then transferred to high temperatures, was not substantially delayed and flowers developed normally. Flowering was delayed 3 days when ‘Surf’ was exposed to high temperatures for 8 weeks from the start of short days. Exposure to high temperatures did not cause bracteate bud formation in ‘Surf’. With both cultivars, increasing the duration of high temperature exposure increased the time to flowering.