Rosetting response was determined for four lisianthus [Eustoma grandiflorum (Raf.) Shinn.] cultivars exposed to photoperiod and temperature treatments during stage 1(14 to 43 days after sowing) and stage 2 (43 to 79 days after sowing) seedling development. Stage 1 seedlings were exposed to short days (12 h photoperiod) or long days (18 h photoperiod) in combination with high (26C) or low temperatures (12C). After stage 1 treatments, stage 2 seedlings were divided and exposed to the same treatment combinations resulting in 16 treatments. Seedlings were then grown at 22C for 120 days to determine rosetting response. Cultivars responded differently to temperature and photoperiod. Short day-high temperature exposure during either stage 1 or stage 2 resulted in the greatest number of rosetted plants (50 to 100%) for `Yodel White', `HeidiPink', and `BlueLisa'. `GCREC-Blue' did not rosette with short day-high temperature. Low temperature during stage 1 did not prevent rosetting when stage 2 seedlings were subsequently exposed to high temperature, but low temperature during stage 2 decreased rosetting of seedlings exposed to high temperature in stage 1. Less rosetting occurred with long day-high temperature than with short day-low temperature, especially for `Blue Lisa'.
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