Effects of seedling age and high and low growth temperatures on bolting ofEustoma grandiflorum (Raf.) Shinn. cultivars

Effects of exposing Eustoma cultivars to high and low growth temperatures f or different durations and with an interval of chilling on bolting were exa mined. In Exp. 1, seedlings of 'Asukanosakura' and 'Asukanoasa' which were grown at 30/25 degreesC (day/night) under a 12-hr photoperiod for 0 to 6 we eks after sowing were exposed to 11 degreesC for 3 weeks and subsequently c ultured at 30/25 degreesC, 27.5/17.5 degreesC, and 22.5/12.5 degreesC. All seedlings of both cultivars grown at 22.5/12.5 degreesC bolted;whereas 13 s imilar to 88% of those grown at 30/25 degreesC bolted. In Exp. 2, seedling of 'Asukanoyosooi' and 'Miyakomomo', grown at 35/25 degreesC for 0 to 8 wee ks under natural photoperiod after sowing, were exposed to 11 degreesC for 5 weeks and then cultured at the above 3 temperature regimes, After the low -temperature treatment, all plants, initially grown for 4 and 6 weeks, bolt ed after 'Asukanoyosooi' and 'Miyakomomo' attained more than 1.1 and 2.3 no des per stem, respectively, independent of the final growing temperatures. Contrarily, seedlings that were initially grown for 0 to 2 weeks prior to c hilling formed rosettes. In Exp. 3, seedlings of 'Azumanosakura', 'Asukanos akura', and 'Asukanoasa' were grown at 35/25 degreesC for 0 to 2 weeks unde r a natural photoperiod after sowing, then exposed to 11 degreesC for 1 to 5 weeks, and then cultured at the original day/night temperatures. Most of the seedlings bolted when they were exposed to the chilling temperature for 3 to 5 weeks, regardless of the initial duration of the treatment. In Exp. 4, when seedlings of the 3 cultivars in Exp.3 were exposed to 35/25 degree sC for 4 to 8 weeks after sowing and subsequently to 11 degreesC for 3 to 6 weeks, all seedlings bolted after 5 weeks of chilling. Thus, we conclude t hat low-temperature exposure is primarily responsible for the bolting of th ese Eustoma cultivars which are hard to form rosettes.