Genetic variation of the control of flowering in kenaf with emphasis on the ambiphotoperiodic response of cultivar Guatemala 4

Abstract

Days to flower of six kenaf ( Hibiscus cannabinus) cultivars (Guatemala 4, Guatemala 51, Everglades 71, CPI 72226, CPI 72246 and CPI 72247) were examined over a range of environments and planting dates. The latitudes of the locations ranged from 17°15′S to 34°33′S. The response of flowering to planting date and location varied with the cultivar. Four of the cultivars (Everglades 71, CPI 72226, 72246, 72247) flowered at all locations and planting dates after the longest day of summer. A short day flowering model, whereby thermal time to flower increases with lengthening photoperiods up to a critical photoperiod which inhibited flowering, was fitted to the data. This model was able to explain more than 84% of the variation in the observed thermal time to flower for the four cultivars at a range of independent locations. There were genetic differences in the parameters such as critical photoperiod and basic vegetative phase among these cultivars. The remaining two cultivars (Guatemala 4 and Guatemala 51) flowered during the long days of summer at locations more southerly than 19°31′S. The short day response, described above, was not adequate to explain this flowering response at lower latitudes. An alternative response named an ambiphotoperiodic response, that has been recorded in other species, was recognised for these cultivars. A simulation model based on the ambiphotoperiodic response of these cultivars explained 92 and 99% of the variation respectively in thermal time to flower at all locations.