Turkish Journal Of Agriculture And Forestry, vol.46, no.2, pp.1-12, 2022 (SCI-Expanded)
Drought, prolonged shortage of available water, is nowadays among the most crucial limiting factors for crop production which is considered as a major threat to food security on the earth. Rootstock selection is among the important approaches for drought management. This research was aimed to study the responses of important rootstocks against drought stress and to examine the impacts of melatonin application on the drought stress of these rootstocks. Carrizo citrange, Flying dragon and sour orange were selected for current study. To test the drought stress, three different irrigation regimes were applicaed separately to each rootstock as 100%, 75% and 50% of water requirement. The melatonin was then tested on each rootstock*irrigation plot with four different doses (0.5 mM, 1.0 mM, 1.5 mM and 2 mM) and a un-treated control application. The impacts of these treatments on root height, shoot height, number of leaves, leaf area, root biomass, shoot biomass, leaf water content, membrane permeability, proline content, chlorophyll content and carotenoid contents were evaluated. Results suggested that melatonin application significantly increase the root and shoot growth of the test rootstocks. Besides to that, the highest root length was noted from Flying dragon, while the Carrizo citrange had the highest shoot height. The number of leaves and leaf are were noted to decrease as the drought stress increase, while the melatonin treatment improved both of these parameters of the rootstocks. As a response to the drought stress, leaf membrane permeability of rootstocks increased and the relative water contents decreased. Both traits was noted to be improved by the melatonin application. In terms of the leaf relative water content and membrane permeability, the Flying dragon rootstock was observed to be more tolerant to drought as compared with the Carrizo citrange and sour orange. Similarly, increase in the drought stress resulted with a reduced chlorophyll and carotenoid contents in the leaves, which was found to be improved by the melatonin application. External melatonin application was finally observed to reduce the proline content in the leaves under drought stress, which is a sign of improvement of the crops tolerance to drought.