Responses of Chlorophyll Fluorescence, Stomatal Conductance, and Net Photosynthesis Rates of Four Rubber (Hevea brasiliensis) Genotypes to Drought

This experiment aimed to evaluate the leaf chlorophyll fluorescence and gas exchange response to drought conditions of young rubber plants with different scions. Buds from four genotypes of a progeny derived from crossed clones of RRIM600 x RRII105 from Nongkhai Rubber Research Center, T187, T186, T149 and T172, were grafted to RRIM 600 rootstocks. Eight-month old plants with two flushes were used in this study. Two levels of water treatment were used, drought condition (W1) and well-watered as control (W0). Leaf chlorophyll fluorescence, stomatal conductance (gs) and net photosynthesis rate (Pn) were investigated in three phases: before drought, during drought and after re-watering. Leaf gas exchange parameters were measured using Li-6400 (LiCor Inc.). Leaf chlorophyll fluorescence was measured using FluorPen FP 100 (Photon Systems Instruments). Before drought, genotype T186 had the greatest net photosynthesis rates followed by T172, T187 and T149; there was no difference in maximum quantum yield of photosystem II (Fv/Fm) and performance index on absorption basis (PIABS). Drought conditions caused reduction in stomatal conductance, net photosynthesis rates, and leaf chlorophyll fluorescence in all genotypes. In re-watering conditions, genotype T186 and T172 experienced quick recovery while the others showed partial recovery but the values of all parameters did not reach previous levels before treatment.