Effects of Temperature On Shoot Apical Development and Flowering In Chrysanthemum Cultivars with Different Heat-Delay Sensitivity

Delayed anthesis is induced by heat in chrysanthemum [Dendranthema ×grandiflora (Ramat.) Kitam. ]. However, research of high temperature effect on developmental phases in chrysanthemum with different flowering-heat-delay sensitivity is presently limited. This study determined day/night temperatures (30/25 °C and 20/15 °C) under 12-h photoperiod conditions on shoot apical development and flowering stages in heat-delay-insensitive ‘Kaa Luoh-Lii’ and heat-delay-sensitive ‘Repulse’. All plants had formed receptacles with shoot apical diameters of ca. 0.35 mm on day 13, and had initiated floret primordia on day 18 for both temperature treatments. On day 46, shoot apical diameter ranged from 9 to 11 mm in ‘Kaa Luoh-Lii’ for both temperature treatments while the apical diameter of ‘Repulse’ was 15 mm at 20/15 °C, compared to only 5 mm at 30/25 °C. Shoot apical stage in ‘Kaa Luoh-Lii’ did not differ between temperature treatments. In contrast, after the initiation of outer floret primordia, ‘Repulse’ had a slower further development at 30/25 °C than at 20/15 °C. Leaf number below the inflorescence did not differ between temperature treatments in both cultivars. The 30/25 °C treatment did not delay any flowering phase in ‘Kaa Luoh-Lii’, but delay the time to show color and anthesis in ‘Repulse’ by 31 days and 33 days, respectively.