First record of off-season flowering in Populus deltoides from India: paradigm of climate change indicator.

Populus deltoides is a fast-growing woody species possessing plethora of industrial applications. This species evolutionarily developed unisexual male and female catkin inflorescence on separate trees. Flowering usually occurs during early spring before the development of foliage, where buds appear near axils or at the extending shoots. In 2019, surveys were undertaken to study the flowering pattern of P. deltoides in the states of Punjab, Haryana, Uttar Pradesh and Uttarakhand in northern India. Interestingly, an anomalous flowering behaviour (appearance of off-season male catkins during autumn, i.e. October) was observed in a plantation trial at Kapurthala, Punjab. The male catkins were 2.7-3.1 ± 0.07 cm long and 0.3-0.5 ± 0.03 cm wide, which is significant for flowering and liberation of pollen grains. Preliminary results suggested that climatic factors, such as episodes of high or low temperature and the precipitation variation forcing the tree species to behave differently. Unearthing the climate-driven off-season flowering in other tree species alluded the stimulation of phytohormones, such as gibberellic and salicylic acid concentrations influencing the flowering time, therefore, needs further investigation in case of P. deltoides. Overall, this work provides early clues of changing climatic scenario altering the flowering pattern of a tropical forestry tree species.