Genetics of production traits in Hevea brasiliensis (rubber). I. Changes in genetical control with age

Abstract

To determine the nature and extent of genetical and environmental control of production traits in rubber trees, nine clones were studied in replicated trials in Sri Lanka at seven sites. The clones represented a range of indigenous and imported germplasm whereas the sites were selected to represent a range of rubber growing areas. Trees were studied for two important production traits over 15 years including 9 years after the initiation of tapping for latex: girth, a measure of vigour, and rubber yield. The results of the analyses of girth data show a consistent increase in heritability over the 15 years from 12 per cent to over 75 per cent with a corresponding decrease in the effect of the environment (70 per cent to 12 per cent). With respect to yield, there was no such change from environmental control to genetic control of the character over the 5 years during which yield was monitored. Correlations between final tree size and earlier measurements indicate that different genes are involved in pre- and post-tapping growth. This implies that post-tapping size measurements alone are useful as predictors of final size. There are nonsignificant but negative correlations between vigour and rubber production. The implications of these findings to breeding and selection of rubber for these two production traits are discussed.