Abstract
Tea (Camellia sinensis L. Kuntze) is widely used beverage in the world. Being a perennial crop it faces abiotic stresses especially drought that significantly affects its growth and yield. Thus, experiments were conducted during 2014-2017 at the Bangladesh Tea Research Institute to screen 345 tea germplasm for drought tolerance based on morpho-physiological and biochemical traits. Amongst 345 germplasm, 205 were selected based on green leaf yield, quality and recovery speed after pruning. From 205 germplasm, best four clones (B/8/93, Mz/39, A/17/7 and Sh/9/65) were selected based on cutting survivability. The six clones were further evaluated for their drought tolerance ability including BT2 (drought tolerant check) and A/8/8 ( drought susceptible check tea clone). The drought was imposed after establishment of the saplings (6-month old) in polytubes (volume 2345 cc) under rain-out shelter maintaining four levels of soil moisture content (36±2 as control, 30±2, 24±2 and 18±2%) measured by tensiometer throughout the growth period at the nursery following Completely Randomized Design with three replications. Required irrigation was provided and soil moisture was calibrated with Neutrone probe under rain-out shelter correspond to same moisture levels (36±2 as control, 30±2, 24+2 and 18±2%) after establishment of the planted saplings in the field. The data were recorded on morphological (plant height, leaf number, total root length, vertical root depth, root volume, R-S ratio, leaf area), growth trait (total dry matter, Absolute Growth Rate; AGR, Relative Growth Rate; RGR and Net Assimilation Rate; NAR), physiological (Chlorophyll stability index, CSI%; relative water content, RWC%), and biochemical (proline, polyphenols, catechins and reducing sugar) for selecting the best drought tolerant tea clone(s). The results were expressed in per cent relative reduction/change compared to control. The results revealed that the drought stress significantly reduced plant height, leaf number, leaf area, root volume, total dry matter, NAR in the A/8/8, BT2 and Sh/9/65 (corresponding figures were for plant height 55.1, 28.2 and 29.6%; leaf number 43.8, 23.8 and 34.6%; leaf area 45.0, 23 and 22%; root volume 35.2, 15.1 and 15.3%; TDM 51.5, 22.6 and 22.4%; NAR 77.1, 84.7 and 84.5%; CSI 22.1, 7.8 and 8.4%, RWC 55.2, 29.2 and 30.4% for the three clones, respectively) compared to the B/8/93, Mz/39 and A/17/7 clones (corresponding figures were for plant height 20.2, 24.8 and 14.7%; leaf number 15.1, 20.3 and 19.7%; leaf area 20.1, 20.7 and 19.4; root volume 6.6, 6.9 and 5.1%; TDM 19.2, 22.6 and 22.5%; NAR 60.8, 67.1 and 68.6%; CSI 6.5, 7.5 and 3.6%; RWC 20.1, 25.2 and 24.1%, respectively). On the other hand vertical root length, R-S ratio, proline, polyphenol, catechin, and reducing sugar contents were significantly higher in the clones B/8/93, Mz/39 and A/17/7 (corresponding figures were for vertical root length 20.5, 15.1 and 14.6%; R-S ratio 12.3, 11.1 and 1.7%; proline 9.4, 8.4 and 8.5%; polyphenol 9.7, 6.7 and 7.4%; catechin 3.6, 2.7 and 2.7%; reducing sugar 6.1, 4.3 and 4.2% for the three tolerant clones, respectively) than that in A/8/8 and BT2 (corresponding figures were for vertical root length 1.2 and 9.8%; R-S ratio 1.7 and 8.9%; proline 1.3 and 6.8%; polyphenol 0.7 and 6.4%; catechin 1.7 and 2.1%; and reducing sugar 2.1 and 3.2% for control drought susceptible and control drought tolerant clones, respectively) under drought. It might be concluded that among the tea germplasm, three clones viz., B/8/93, Mz/39 and A/17/7 appeared drought tolerant based on yield, morpho- physiological traits and beverages quality.