Water stress induced by consecutive years of drought constitutes a major constraint for citric culture in Fars province in Iran. The aim of this study was rapid and accurate screening of citrus seedling rootstocks (grown under greenhouse conditions) in terms of drought tolerance and ability to recovery, using chlorophyll fluorescence technique combined with measuring the leaf gas exchange parameters. Eight month-old seedlings of Mexican lime, sour orange, Volkameriana and Rangpur lime plants were submitted to a cycle of drought for 14 days/rewatering for 3 days and control plants were maintained in an optimal soil water condition during the whole experimental period. At the end of stress and recovery periods, measurements were made using fully developed leaves. According to F v/F m ratio index, treated Volkameriana plants had no significant photoinhibitory damage to PS II. Rewatered Mexican lime and Rangpur lime plants had ability to fully recover the significantly reduced fluorescence index, but in sour oranges, full recovery did not happened. Also, our results indicated that the rate of net photosynthesis ( A), transpiration ( E) and stomatal conductance ( gs) significantly reduced under drought stress, only Volkameriana and Mexican lime plants fully recovered from stress. Increased Ci in concomitant with stomata closure means a reduction in CO 2 photoassimilation and is a symptom of photoinhibition (in addition to decreased F v/F m ratio, maximum quantum yield of PS II). So, it seemed that at the end of drought period, except for Volkameriana, stomatal limitation combined with PS II photodestruction were responsible to significant reductions in net photosynthesis in treated plants. In other words, in stressed Volkameriana plants only stomatal closure caused the reduction in photosynthesis. Also it was demonstrated that in rewatered sour orange and Rangpur lime plants damage imposed to PS II and lack of recovery in stomatal conductance were major obstructions in photosynthesis recovery, respectively. Finally, it was concluded that Volkameriana seedlings were more tolerant and had better recovery ability and Mexican lime plants had profound ability to recover from imposed negative effects of water stress, too.
