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 occ urred at 29/26 and 34/26 C. Temperatures of 29/21 C or lower reduced d ry weight by more than 50%. Leaf number, leaf weight, and leaf area we re more sensitive to changes in day temperature, whereas plant height and root, stem, and total dry weight were more sensitive to night temp erature. Dry matter production was more closely correlated with leaf a rea duration than with its other component, net assimilation rate. Lea f appearance rate and dry matter production were linearly related to a verage daily temperature. The low-temperature threshold for leaf produ ction was 13 +/- 1 C. Observations of plant development in photoperiod s ranging from 10 to 16 h confirmed that sicklepod is a short-day plan t with a critical day length of 13 to 14 h. No reproductive developmen t 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 init iate and continue reproductive development. Plants from a North Caroli na population flowered earlier than plants from a Florida population i n photoperiods of 12, 13, or 14 h, but in an 11-h photoperiod the two populations flowered at the same time.