Effects of Temperature and Photoperiod on Growth and Development of Sicklepod (Cassia obtusifolia)
Sicklepod was grown in controlled-environment chambers in 16 day/night temperature regimes ranging from 19/11 to 34/26 C. Maximum dry weight, leaf area, plant height, node number, and leaf number after 46 d occurred at 29/26 and 34/26 C. Temperatures of 29/21 C or lower reduced dry weight by more than 50%. Leaf number, leaf weight, and leaf area were more sensitive to changes in day temperature, whereas plant height and root, stem, and total dry weight were more sensitive to night temperature. Dry matter production was more closely correlated with leaf area duration than with its other component, net assimilation rate. Leaf appearance rate and dry matter production were linearly related to average daily temperature. The low-temperature threshold for leaf production was 13 ± 1 C. Observations of plant development in photoperiods ranging from 10 to 16 h confirmed that sicklepod is a short-day plant with a critical day length of 13 to 14 h. No reproductive development occurred in photoperiods of 15 or 16 h. Seedlings that emerged in 10-h photoperiods required more than 1-wk exposure to short days to initiate and continue reproductive development. Plants from a North Carolina population flowered earlier than plants from a Florida population in photoperiods of 12, 13, or 14 h, but in an 11-h photoperiod the two populations flowered at the same time.