CHLOROPHYLL FLUORESCENCE FOR WATER DEFICIT DETECTION IN HORTICULTURAL CROPS?

The potential of chlorophyll fluorescence as a technique for the early detection of plant response to environmental stresses was assessed in a collaborative project. Results are presented that compare the sensitivity of gas-exchange and fluorescence variables to water deficit in potted seedlings of Ziziphus rotundifolia in India. Three days after withholding water, the stomatal conductance and assimilation rate of the unirrigated plants were significantly lower than for the well-watered treatment, however there were still no significant differences between treatments in the fluorescence ratios F_v/F_m, dF/F_m or non-photochemical quenching (q_NP). It is concluded that during the early development of water deficit, stomata control leaf water deficit effectively and electron transport capacity is little affected by changes in assimilation rate. F_v/F_m and dF/F_m are not sensitive indicators of water deficit, while q_NP has some potential.