STUDIES ON NATURAL HYBRIDS OF <em>ACACIA</em> <em>MANGIUM</em> AND <em>A</em>. <em>AURICULIFORMIS</em> IN VIETNAM

Abstract

Natural hybrids of Acacia mangium and A. auriculiformis have been found in A. mangium plantations in Vietnam. Hybrids found at Ba Vi are derived from the Daintree (Queensland) provenance of A. mangium and the Darwin (Northern Territory) provenance of A. auriculiformis. F₁ hybrid trees in Vietnam have
morphological characteristics intermediate between those of the two parent species, and marked hybrid vigour in growth. At 2.5-3 y, the hybrids produced 100-600% greater stem volume than A. mangium and A. auriculiformis. At 4.5 y of age the hybrids produced, on average, twice the stem volume of A. mangium. Wood density of the hybrid is intermediate between the values of the two parents. Paper pulp productivity, and the breaking strength, folding endurance and brightness of paper produced from the wood of the hybrid are superior to those of the parent species. Plus trees were selected from among the F₁ hybrids from Ba Vi, and cutting propagation and clonal tests of these individuals were established. At age 2 y, selected hybrid clones displayed markedly better growth than cuttings and seedlings of the two parent species. Integrated assessment of growth, stem straightness, branch size and tree health were used to select the five best hybrid clones, one of which is outstanding for growth and stem form. The five best clones have been propagated by tissue culture of meristems, and are being tested in trial programmes in the main ecological regions of Vietnam.