Exposure to drought stress during the grain development in wheat results in the reduction in grain weight. This reduction varies across the length of the spike. Several factors might be contributing to this variation. Photosynthesis can be one of them. We hypothesised that quantum yield of photosystem-II (PS-II) can be a potential trait to improve the grain weight and productivity of wheat. Ten wheat genotypes varying in their spike morphology were subjected to well-watered and water stressed conditions during grain development. At 22 and 25 days post anthesis, three spikes from main stems were collected for each genotype and treatment and immediately analysed using flourocam. Two areas from each of the three regions of the spike (apical, middle and basal) were selected for measurement of maximum quantum yield. The genetic variation in the photosynthetic efficiency of PS-II under both treatments was mainly contributed by the apical (top) spikelets as the bottom and middle spikelets did not show significant variation among the genotypes. The apical spikelets had lowest average potential quantum yield of all the genotypes and the basal spikelets had the highest. The study could differentiate sensitive and tolerant genotypes with respect to their capacity to maintain high PS-II efficiency in the spike even under insufficient soil moisture conditions relative to plants grown with sufficient soil moisture. The better PS-II efficiency in the terminal spikelets despite water stress condition may improve grain weight.