COMPONENTS OF VARIANCE AND INTERACTION BETWEEN GENOTYPE AND ENVIRONMENT FOR ANNUAL GIRTH INCREMENT IN RUBBER TREE

To determine the nature and extent of genetical and environmental cont rol of vigour through annual girth increment in rubber trees [Hevea br asiliensis (Willd, ex Adr. de Juss.) Muell. Arg.], seven clones were s tudied in a replicated trial in Sao Paulo State at four different loca tions. The clones represented a range of imported germoplasm while the locations were selected to represent a range of rubber growing areas. Trees were studied for annual girth increment over five years before the initiation of tapping for latex. The results of the analyses show a consistent decrease in genetic component over the five years from 10 per cent to 0.5 per cent with a corresponding increase in the effect of environment (19.0 per cent to 93.0 per cent). The genotype x enviro nment effects from combined analysis were significant for three factor analysis of variance. Genetic correlations between locations for annu al girth increment revealed a consistent positive and significant corr elation between Mococa and Matao in the fifth year (r(g) = 0.7128), Ri beirao Preto and Matao in the fifth year (r(g) = 0.7113) and Ribeirao Preto and Presidente Prudente in the fourth year (r(g) = 0.9367). The implications of these findings in selection of rubber for annual girth increment trait are discussed.