Pot Culture Experiment on Screening for Tolerance to Drought in a Set of Wild Hevea Germplasm

India received 4,548 wild germplasm accessions of Hevea brasiliensis as a result of the expedition conducted by International Rubber Research and Development Board in 1981 in the Amazon forests of Brazil, mainly concentrating in three states, namely Acre (AC), Rondonia (RO) and Mato Grosso (MT). This wild germplasm collection is conserved at Rubber Research Institute of India (RRII) and is now in various stages of evaluation. Wide variability observed in this large collection indicated a broad genetic base, potentially important in broadening the existing narrow genetic base of cultivated rubber. Being a likely repository of genes conferring tolerance to various biotic and abiotic stresses, this wild collection is useful in developing Hevea clones tolerant to stresses. For identifying the drought tolerance potential of this germplasm collection, a pot culture experiment was conducted at RRII using a set of 16 wild accessions along with the check clones RRII 105, RRII 208, RRIM 600 and Tjir 1. Data recording on growth and drought related morphological, physiological and anatomical parameters was done for assessing the clonal response of these accessions to drought stress. Plant height, girth, number of whorls, number of leaves, distance between whorls and petiole length were the growth parameters studied. As a physiological parameter, after noon leaf water potential (LWP) was recorded during the summer months after withholding irrigation and drought related anatomical parameters studied were xylem characteristics and intra-xylary phloem in twigs. Morphological characterization based on drought sensitive parameters such as leaf size, appearance of leaf surface, presence or absence of wax coating on leaf surface, leaf yellowing and senescence and vigor of plant was done and mortality rate among the accessions was assessed for identifying the potential drought tolerant accessions. It was found that among the 16 wild accessions studied, the accessions MT 1681 and MT 1623 were the potential ones for further detailed field evaluation towards developing a drought tolerant Hevea clone.