Early selection for growth vigor in rubber tree genotypes in northwestern Sao Paulo State (Brazil)

Forty-five genotypes (clones) of rubber tree [Hevea brasiliensis (Willd. ex Adr. de Juss.) Muell. Arg.] of differ ent origins were assessed for effici ency of early selection at the Votuporanga Experimental Station in north-we stern Sao Paulo State, Brazil, using a randomized complete block design wit h three replications and six plants per plot. Girth at 120 cm above the hig hest point of the grafting union of each tree was taken at ages 12, 24, 36, 48, 60, 72, 84 and 96 months. Highly significant differences in girth were detected among the genotypes at all ages evaluated, except for 12 months. Estimates of genetic variance for two age sets showed a substantial increas e with age, while the genotype variation decreased. Selection made at 24 mo nths proved to be the most efficient, giving a superior gain per unit of ti me.