Ontogenetic variations in flush development are indicative of low temperature tolerance in Hevea brasiliensis clones

Para rubber (Hevea brasiliensis) trees are naturally adapted to the Amazonian tropical climate. In India rubber trees are traditionally cultivated in the warm humid tropics of the south. Northeast India is a non-traditional area for rubber cultivation. A major limiting factor on tree growth in the northeast region is stress due to low temperature. Being a deciduous tree, rubber trees exhibit annual natural defoliation prior to the winter season, and ensuing new leaf growth usually coincides with the low temperature period. Flushing behaviour of trees during this period provides an opportunity to assess their winter hardiness. A study was carried out on five clones, RRIM 600, SCATC 93/114, GT 1, PB 5/51 and Haiken 1, to evaluate phenological behaviour of leaf growth during the period of low temperature stress. Trees were monitored for expansion of leaf area, internode length, petiole length and development of chlorophyll. Wide variation was observed among these clones for all the traits. SCATC 93/114 was better adapted for low temperature stress as this clone was found to have faster expansion of leaf area and better chlorophyll development, followed by Haiken 1. PB 5/51 was found to show poor performance during low temperature. Haiken 1 and PB 5/51 also exhibited better relative growth rate during winter months confirming their low temperature tolerance. Ontogenetic variations in leaf development are good indicators of assessing inherent cold tolerance in Hevea clones.