Age trends in the genetic control of production traits in Hevea

Seven clones were studied, at four locations ,in replicated trials, in Sao Paulo State, Brazil, to determine the nature and extent of the genetic and environmental control of yield and girth traits in rubber tree [Hevea brasiliensis (Willd. ex Adr. de Juss.) Muell.-Arg.]. The clones represented a range of recommended material for planting, whereas the locations were selected to represent a range of rubber growing areas. Trees were studied for yield and girth over 11 years including three years after the initiation of tapping for latex: girth, vigor, and rubber yield. Girth analyses data showed a consistent increase in genotype component over the pre-tapping stage from 16 percent to 40 percent, with a corresponding decrease in the effect of the environment (71 percent to 38 percent). With respect to yield there was a similar change from environmental control to genetic control of the trait over the three 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 posttapping size measurements alone are useful as predictors of final size. There are non significant 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.