The objectives of the study were to determine the differences in tree performance among teak clones, to confirm the previous test (first study), and to produce improved genetic materials for teak farmers in Northeastern Thailand. The experiment was undertaken with a randomized complete block design (RCBD) with four replications. Each replication contained three ramets of each clone planted in a row (3 line plot). Twenty-five clones were selected based on the results of the previous field trail (first study), full-sib progeny, teak improvement program, and newly added trees from Navamin teak forest in Mae Hong Son province. In total, 300 seedlings (25 clones × 3 trees/plot × 4 replications) were planted in Khon Kaen province, Thailand.
The preliminary results of height (H), diameter at ground level (DGL), and stem form were evaluated when the seedlings reached 1 year old. In terms of clone performance, statistical analysis showed that there was a significant difference in current annual increment (CAI) of H and DGL of seedlings among clones. The average CAI of H and DGL of each clone were 1.11 m and 1.47 cm ranging from 0.56 to 1.45 m and 0.76 to 1.76 cm, respectively (n = 244). Based on Duncan’s multiple range test, clones no. 219, 8c20, MH7 3bb/38, 119, 302, and 300 showed high performance in CAI of H. Among the 25 clones, clone no.3bb/38 showed especially good performance in growth (DGL = 1.69 cm and H = 1.25 m) and stem form. Regarding stem characteristics, we found variations of stem form within and among clones. The forms were classified as four types: straight stem, V shape, branchy, and multi-stem.