AN ANALYSIS OF GROWTH AND DROUGHT TOLERANCE IN RUBBER DURING THE IMMATURE PHASE IN A DRY SUBHUMID CLIMATE

An experiment with the objective of evaluating the performance of 15 c lones of rubber (Hevea brasiliensis) was conducted in the Konkan regio n of Western India. The clones under evaluation were RRII 5, RRII 6, R RII 105, RRII 208, RRII 308, RRIC 52, RRIC 100, RRIC 102, RRIC 105, RR IM 605, PB 260, PB 310, PB 311, PR 255, and PR 261. The region is a tr ial environment for the crop and experiences more than seven rainless months and severe drought in the summer months. Data on monthly girth growth were collected for six years from a trial with randomized block design. The growth of clones in terms of monthly girth increment grow th (GIN, cm month(-1)) seasonal mean girth increments (MGIN, cm season (-1)) and mean relative increment rates (MRIR, mm cm(-1) season(-1)) a s well as annual MGIN (cm a(-1)) and MRIR (mm cm(-1) a(-1)) was studie d. Correlation analysis was performed to understand the effect of seas onal growth on the final growth. At the beginning of the study, the la rgest girth noted was for the clone RRII 6 (22.5 cm) followed by RRII 208 (22.0 cm). PR 261 with a girth of only 14.2 cm was the least vigor ous among the clones. A large portion of the growth occurred in the we t season only. During the dry season the growth rates of the clones de clined substantially and decreases in girth ranging from 0.2 mm to 0.5 mm were noticed in most of the clones. Al the end of the study period the largest girth observed was for clone RRII 208 (49.3 cm) and the l owest for PR 261 (39.3 cm). The highest proportion of tappable trees n oted was for clone RRII 208 (52.4%) and the lowest for PR 261 (2.7%). The pooled average of tappable trees was only 17.5%. The data revealed that the immaturity period for Hevea in the region will not be less t han 9 years under rainfed conditions. From the analysis based on the f inal girth it was concluded that clones RRII 208, RRIC 52, RRII 6, RRI C 100 and RRIC 102 are more tolerant to drought while RRII 105, RRIC 1 05, RRII 5, RRIM 605, PB 310, PB 260, PB 311, PR 255, RRII 308 and PR 261 are less tolerant. The results of correlation indicated that by an alysing the growth, potentially drought-tolerant clones can be identif ied.