Seed germination of Echinopsis schickendantzii (Cactaceae): the effects of constant and alternating temperatures

The effects of constant and alternating temperatures on seed germination in the Cactaceae have been reported to vary, probably as a result of the different temperature regimes used and the species considered. We determined the cardinal temperatures for, and evaluated the effects of a wide range of constant and alternating temperatures on, seed germination of the South American cactus, Echinopsis schickendantzii Web. The base, optimum and maximum temperatures were 7°C, 26.8°C and 49°C, respectively. The proportion of seeds that germinated and the germination rates were not only significantly different at constant and alternating temperatures but also among all temperature regimes considered. The highest proportion of seeds to germinate occurred at 15°, 20°, 30° and 30/15°C whereas the highest germination rates occurred at 25°, 30°, 30/20°, 35/20° and 40/25°C, with no significant differences between the highest values at constant and alternating temperatures. In the suboptimal temperature range for germination rate, the thermal time to 50% germination was 98°C-days. The results indicate that the seeds have no obligate requirement for alternating temperature for germination.