Temperature-dependent variation in flowering time and membrane electrolyte leakage among Eustoma cultivars

• Mean daily temperature strongly regulated leaf initiation and flowering in Eustoma grandiflorum , with rates increasing up to 22.6 °C and declining at higher temperatures. • Base temperatures for leaf initiation varied among cultivars (2.8–3.5 °C), being lowest in early- and highest in late-flowering types. • Cultivars are traditionally classified as early-, medium-, or late-flowering based on plants grown at 15–20 °C, but this system is less reliable at higher temperatures. • Optimal growth and flower quality occurred near 23 °C, while flower quality declined above 28 °C due to shortened vegetative growth. • Cold sensitivity, assessed by electrolyte leakage, was higher in late-flowering cultivars and correlated with delayed flowering at low temperatures. Temperature strongly regulates developmental timing and flower quality in Eustoma , yet quantitative models describing this relationship are limited. This study quantified the effects of mean daily temperature (MDT) on leaf initiation and flowering in Eustoma cultivars differing in earliness, and assessed cultivar-specific cold sensitivity via leaf electrolyte leakage. Leaf initiation rates increased with MDT up to 22.6 °C but declined at higher temperatures. Base temperatures (Tb) for leaf initiation ranged from 2.8 for early- to 3.5 °C for late-flowering cultivars. Leaf number below the first flower decreased as MDT increased from 14.0 to 32.7 °C. Increasing MDT reduced leaf number below the flower and shortened the time to flowering, while late-flowering cultivars were more sensitive to low temperature and failed to flower at 14 °C. Optimal vegetative growth and flower quality occurred near 23 °C, but flower quality declined above 28 °C. Electrolyte leakage at low temperatures correlated with delayed flowering in late-flowering cultivars, indicating cold sensitivity as a key factor in developmental variation. This study provides the first quantitative model linking thermal time, cultivar-specific base temperature, and cold sensitivity to flowering behavior in Eustoma .