Season and genotype effect on whole plant water use efficiency of coconut (Cocos nucifera L.) seedlings grown in a hydroponic system

•Significantly high water use in summer than monsoon, biomass change non-significant.•WUE of dwarfs was low during summer compared to talls.•Stomata was insensitive to high VPDL in dwarfs while sensitive in talls.•High PAR during summer might be limiting biomass gain in dwarfs. A study was conducted to understand the influence of climatic factors on nutrient use, and whole plant water use efficiency (WUE) of hydroponically grown coconut seedlings. Two dwarf (Chowghat green dwarf, CGD and Malayan yellow dwarf, MYD) and two tall (Kalpa Pratibha, KP and Kalpatharu, KT) coconut genotypes were grown in triplicates and their water use, and biomass production were measured and WUE was analyzed across summer, monsoon and winter seasons, characterized with distinct climatic variability. In comparison to monsoon, during summer the morning temperature was (6 ℃) high, and relative humidity (RH) was low during summer resulting in two folds increase in vapour pressure deficit on leaf surface (VPDL). Increasing VPDL had direct influence on water consumption of the plant per day which was significantly high during summer (3.14 L) compared to monsoon (1.83 L), but the difference in biomass gain was not significant. This had led to a weakly negative [R2(144) =0.12, p