Modeling the interactive effect of the photoperiod and temperature on shoot elongation of mulberry

Potted mulberry plants (Morus alba L. 'Shinn-ichinose') were grown in phytotrons under natural sunlight, and their shoot growth response to temperature and photoperiod was investigated. A short photoperiod caused cessation of shoot growth, and this effect was prominent at 20degreesC. Temperatures higher than 24degreesC activated the growth activity for mulberry shoot growth. Temperature had two effects on mulberry shoot elongation. One was to control the growth activity of mulberry shoots, and the other was to determine the potential rate of shoot elongation, which is realized at the maximum growth activity under a given environmental condition. On the basis of these results, the effect of temperature and photoperiod on the cessation of mulberry shoot elongation was simulated in a non-linear regression model. The values of shoot length predicted by the model differed somewhat from the measured values in some plots, most likely because the timing of shoot growth cessation differed with the year. However, on the whole, shoot length predicted by the model seems to fit the measured values well.