Evidence that banana (Musa spp.), a tropical monocotyledon, has a facultative long-day response to photoperiod.

Bananas and plantains (Musa spp.) may flower at any time of the year but they show seasonal variation in flowering. To determine whether photoperiod contributed to this seasonal variation, we calculated the thermal development units (DT) from planting to bunch appearance (flowering) using data from published planting date experiments in the tropics and subtropics. Minimising the coefficient of variation in DT across planting dates was used to evaluate the contribution of photoperiod and soil water balance to time of flowering. Coefficients evaluating sensitivity to photoperiod were estimated in some datasets and validated on independent datasets. Data on the rate of bunch appearance from four locations over several years were analysed to establish correlations between this, photoperiod and temperature. The time of bunch initiation was matched against photoperiod to determine whether short photoperiods delayed bunch initiation. Long photoperiods in the mid-vegetative phase hastened flowering while soil water deficits delayed it. Cultivars of the Cavendish subgroup (AAA) were more sensitive to photoperiod than the Maricongo cultivar (False Horn-type plantain, AAB). Long photoperiods during the reproductive phase were correlated with an increased rate of bunch appearance some 8 to 11 weeks later. Musa spp. show a facultative long-day response to photoperiod.