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

Abstract

An experiment with the objective of evaluating the performance of 15 clones of rubber (Hevea brasiliensis) was conducted in the Konkan region of Western India. The clones under evaluation were RRII 5, RRII 6, RRII 105, RRII 208, RRII 308, RRIC 52, RRIC 100, RRIC 102, RRIC 105, RRIM 605, PB 260, PB 310, PB 311, PR 255, and PR 261. The region is a trial environment for the crop and experiences more than seven rainless months and severe drought in the summer months. Data on monthly girth growth w ere collected for six years from a trial with randomized block design. The growth of clones in terms of monthly girth increment growth (GIN, cm month⁻¹) seasonal mean girth increments (MGIN, cm season⁻¹) and mean relative increment rates (MRIR, mm cm⁻¹ season⁻¹) as well as annual MGIN (cm a⁻¹) and MRIR (mm cm⁻¹ a⁻¹) was studied. Correlation analysis was performed to understand the effect of seasonal growth on the final growth. At the beginning of the study, the largest 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 vigorous among the clones. A large portion of the growth occurred in the wet season only. During the dry season the growth rates of the clones declined substantially and decreases in girth ranging from 0.2 mm to 0.5 mm were noticed in most of the clones. At the end of the study period the largest girth observed was for clone RRII 208 (49.3 cm) and the lowest for PR 261 (39.3 cm). The highest proportion of tappable trees noted was for clone RRII 208 (52.4%) and the lowest for PR 261 (2.7%). The pooled average of tappable trees was on ly 17.5%. The data revealed that the immaturity period for Hevea in the region will not be less than 9 years under rainfed conditions. From the analysis based on the final girth it was concluded that clones RRII 208, RRIC 52, RRII 6, RRIC 100 and RRIC 102 are more tolerant to drought while RRII 105, RRIC 105, 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 analysing the growth, potentially drought-toleran t clones can be identified.