Reproductive development in subterranean clover (Trifolium subterraneum L.): A reanalysis of Oceania datasets

Abstract

Abstract Quantification of thermal time requirements for flowering in subterranean clover is vital to inform cultivar choice on farm, management strategies and for predictive purposes in biophysical models. As an annual crop, the viability of subterranean clover relies on its ability to regenerate by reaching flowering and setting seeds to establish the crop in the following growth season. This study reanalysed published datasets on flowering time of subterranean clover to estimate thermal-time requirements, considering interactions between genotypes and environmental aspects (temperature and photoperiod). Fifteen peer-reviewed publications from New Zealand and Australia were used that included 369 independent data points from 1955 to 2000. The estimated time from sowing to flowering ranged from 44 to 271 days or 628–2600 °C d. Temperature was the main driver of flowering, but photoperiodism influenced subterranean clover reproductive development. There was a strong hysteresis in the relationship between time to flower and photoperiod (Pp), depending on the Pp direction (increasing or decreasing Pp). Explanatory functions in response to photoperiod value and direction were estimated for different genotypes (“early” and “late”-cycle cultivar groups). There was a strong seasonality explained by a total requirement of 1090 ± 94.8 °Cd or 740 ± 79.8 °Cd for late and early cultivars in an increasing photoperiod. In a decreasing photoperiod the thermal time target increased at a rate of 977 ± 90.9 °Cd/h and 834 ± 68.7 °Cd/h for late and early cultivars, respectively.