POTENTIAL FOR GENETIC-IMPROVEMENT OF OIL PRODUCTION IN MELALEUCA-ALTERNIFOLIA AND MELALEUCA-LINARIIFOLIA

Variation in oil yields from plantations and natural stands of Melaleu ca alternifolia (Maiden and Betche) Cheel indicates considerable poten tial for improving plantation production through breeding. Some popula tions of the more widely distributed species, M. linariifolia Sm., pro duce a similar leaf oil and may provide opportunities to expand the ge netic base of plantations. Growth and oil traits were assessed for 60 half-sib families, representing three chemical forms of Melaleuca alte rnifolia, and 10 half-sib families of the terpinen-4-ol rich chemical form of M. linariifolia, in a provenance/progeny trial in northern New South Wales, Australia. Differences in oil composition and coppicing between the terpinen-4-ol rich forms of the two species were significa nt (P < 0.05), while differences in growth traits and leaf oil yield w ere not significant. The difference in oil composition between norther n and southern populations of M. linariifolia was as great as differen ces between the two species, suggesting the two regions should be cons idered distinct races for breeding purposes. Narrow-sense heritabiliti es in M. alternifolia of 0.67 for oil yield, 0.25 for plant dry weight , and 0.27 for coppice indicate substantial improvement would follow s election for single traits. However, negative genetic correlations bet ween oil yield and plant dry weight indicate it is not possible to sim ultaneously achieve major gains in the two traits. Using combined inde x selection with a restriction on plant dry weight, expected gains of 17% in oil yield and 14% in coppicing are predicted from one generatio n of selection at an intensity of one tree in ten.