The dry rubber yield, girth of the trees, biochemical composition (phenols, aminoacids, sugars, protein and glutathione) and the activities of antioxidant enzymes peroxidase (PER), ascorbate peroxidase (APOX), superoxide dismutase (SOD) and polyphenol oxidase (PPO) in the leaf and bark tissues of ten rubber (Hevea brasiliensis) trees each belonging to low and high yield and low and high girth categories were determined during summer (peak drought) and post-monsoon (drought free) seasons during 1996-1998. During this period, the mean dry rubber yield of low yield category trees ranged from14.4 to 34.9 g/tree/tap and for the high yield category it was 32.3 to 107.7 g/tree/tap, depending upon the seasons. The mean girth ranged from 27.5 to 30.2 cm and 76.5 to 82.9 cm for the low and high girth category trees, respectively. The biochemical composition and enzyme activities of the leaf and bark tissues of the four categories showed wide variations. The glutathione content in the bark was higher in the high yielding than in the low yielding trees, irrespective of the seasons. The high yielding trees showed greater PER and APOX activities in the leaves and lower PPO activity in the bark than the low yielding trees. High girth trees consistently showed increased leaf PER activity compared to low girth trees during both the seasons indicating their intrinsic drought tolerance capacity. The possibility of using the above parameters as markers for drought tolerance is discussed.
Active oxygen species, Antioxidants, Drought tolerance, Environmental stress, Hevea brasiliensis
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