Effects of exposing Eustoma cultivars to high and low growth temperatures for different durations and with an interval of chilling on bolting were examined. 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 weeks after sowing were exposed to 11 degreesC for 3 weeks and subsequently cultured 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 similar 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 weeks 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, bolted after 'Asukanoyosooi' and 'Miyakomomo' attained more than 1.1 and 2.3 nodes per stem, respectively, independent of the final growing temperatures. Contrarily, seedlings that were initially grown for 0 to 2 weeks prior to chilling formed rosettes. In Exp. 3, seedlings of 'Azumanosakura', 'Asukanosakura', and 'Asukanoasa' were grown at 35/25 degreesC for 0 to 2 weeks under 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 degreesC 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 that low-temperature exposure is primarily responsible for the bolting of these Eustoma cultivars which are hard to form rosettes.
