Y. SEDI and L.R. HUMPHREYS
Department of Agriculture, University of Queensland, Brisbane, Australia
Seedlings of Sesbania spp. were grown in controlled environments to shed light on the ways in which flowering and seed production are influenced by climate. The 2 Sesbania spp. behaved differently. Flowering of Sesbania sesban var. nubica CPI 30071 was independent of daylength over the range 11–13 h but was inhibited by warm temperature of 33°C day/28°C night. Flowering of S. cannabina var. cannabina CPI 29977 and CQ 1433 showed an interaction between temperature and daylength; flowering was enhanced in short days and reduced in the warm conditions of 33/28°C and 13 h daylength.
In a further study, dissection of lateral apices of CQ 1433 indicated that the transition from a vegetative phase to floral initiation occurred after exposure to 10 short days. The rates of progress towards flowering, expressed as the reciprocal of days to flowering, were linear functions of temperature at 10.5 and 11.5 h daylength. At longer photoperiods, interactions between temperature and daylength contributed significantly to the regression equation. A third experiment showed that continued flower differentiation in CQ 1433 after floral initiation had occurred was promoted by short days; long days arrested further flowering and induced bud abscission. Plants grown at 14.5 h and 32/26°C reverted to the vegetative state; seed production would be low in warm temperatures and increasing daylength, as occur in spring and summer.
CPI 30071 was late flowering; it did not produce seed after 178 d but flowered best at 23/18°C. Maximum seed production of CPI 29977 occurred at 28/23°C and 13 h daylength, whereas seed yield of CQ 1433 was greatest at 33/28°C and 12 h photoperiod. In these two accessions, high temperature and short daylength stimulated flower production but reduced seed number per pod and 100-seed weight; in CQ 1433 these conditions also reduced pod setting. Hardseededness in CQ 1433 was negatively associated with seed moisture content and was higher at 33/28°C than at 28/23°C.
The implications of these experiments for the selection of sites with a high potential for seed production of Sesbania spp. merit field study.