GROWTH TRENDS, GENOTYPE-ENVIRONMENT INTERACTION AND GENETIC GAINS IN 6-YEAR-OLD RUBBER TREE CLONES (HEVEA) IN SAO-PAULO STATE, BRAZIL

Budwood from seven different clones of rubber tree [Hevea brasiliensis (Willd. ex Adr. de Juss.) Muell. Arg.] was planted in replicated tria ls in four different test sites in the plateau region of the state of Sao Paulo, Brazil. The clones represented a range of imported germplas m, whereas the locations were selected to represent a range of rubber growing areas. Girths were measured for six years consecutively, befor e the initiation of tapping for latex. Total number of latex vessel ri ngs (Ivr) and bark thickness (bt) were measured at six years. The larg est average for all characters was observed in Matao. Overall means fo r girth, total number of latex vessel rings and bark thickness at six years were 35.26 cm, 11.30 units and 4.83 mm, respectively. Both the t est sites and clones showed statistically significant. differences in girth, Ivr and bt values. There were significant clone x site interact ions. Girth at one year was not a reliable predictor of future field p erformance. Broad sense heritability for girth was 0.16, and for Ivr a nd bt it was 0.28 and 0.40, respectively, at six years. Repeatability was quite high, from 0.52 to 0.75 for all characters in all years. Whe n two clones out of seven were selected, expected genetic gain in girt h was about 2.0%; for Ivr and bt it was 7.0% and 14.6%, respectively.