INTERSPECIFIC HYBRIDIZATION AND INBREEDING EFFECT IN SEED FROM A EUCALYPTUS-GRANDIS X EUCALYPTUS-UROPHYLLA CLONAL ORCHARD IN BRAZIL

We used allozyme markers to estimate the amount of natural hybridizati on between Eucalyptus grandis and E. urophylla in a 7.4-hectare commer cial hybrid-seed orchard planted in Espirito Santo, Brazil. This orcha rd was planted in 1982 using a honeycomb design, with each hexagonal p lot containing one E. grandis tree surrounded by six E. urophylla tree s. There were 267 replicated hexagonal plots in the orchard. Seeds wer e harvested from the E. grandis clone only. The multilocus outcrossing rate estimated for the E. grandis clone averaged 70.2%, ranging from 33.0 to 99.0% among individual trees. Contaminant pollination, inferre d from progeny genotypes containing alleles not present in the seven p arental clones, accounted for 14.4% of the hybrid seed. Contaminant po llen was attributed to neighboring eucalyptus stands isolated from the orchard by a 400-m wide belt of native forest. Inbred and hybrid prog enies were identified by their allozyme genotypes and transplanted to the field. Field growth of inbred progeny was 30% lower than that of h ybrid plants at two and three years of age.