Genotype-environment interaction and the number of test sites for the genetic improvement of rubber trees (Hevea) in Sao Paulo State, Brazil

The present study quantifies the possible genotype-environment interactions and determines the ideal number of test sites for rubber trees [Hevea bras iliensis (Willd ex Adr. de Juss.) Muell Arg] in the plateau region of Sao P aulo State. The study was based on the genetic correlation among progenies at three different sites and on estimates of genetic gains with indirect se lection of rubber trees. Twenty-two half-sib progenies were planted at the Jau, Pindorama and Votuporanga experimental stations using random blocks wi th five replications and 10 plants per plot. At three years of age, the pla nts were evaluated for their total number of latex ring vessels (NR), rubbe r production (RP), bark thickness (BT) and girth (SG), There was significan t genetic variability in the characters RP, SG and BT, mainly among progeni es from Pindorama and Votuporanga. The effects of genotype-site interaction s were significant for RP and SG. The finding of significant interactions w as not a complicating factor because of the large generic correlation detec ted. These results indicate that the use of two sites is more profitable wh en the gains in efficiency of selection are greater than 10%. Thus: Pindora ma and Votuporanga will satisfactorily attend the studied region.