VERIFICATION OF TOLERANCE TO INFECTION BY <em>CERATOCYSTIS</em> <em>MANGINECANS</em> IN CLONES OF <em>ACACIA</em> <em>MANGIUM</em>

Abstract

Ceratocystis canker and wilt disease has had a devastating impact on plantations of Acacia mangium in Sabah, Malaysia effectively resulting in its discontinuation in the region. The immediate future of industrial tree plantations in Malaysia relies on alternative species, such as Eucalyptus pellita, which are suited to the environment and market opportunities. However, identifying A. mangium planting stock with high levels of tolerance to Ceratocystis manginecans provides substantial opportunities for its large scale planting and sustainability in the future. The aim of this study was to verify tolerance to C. manginecans in over 100 putatively tolerant A. mangium clones selected from a family screening trial consisting of 100 wild families. Selections from the family screening trial were based on either short-lesion length measured six weeks after inoculation or survival 12 months post inoculation. Six clonal trials were established under field conditions over two years with more than five ramets of most clones tested in at least two separate trials. The trees were inoculated with C. manginecans 12 months after trial establishment, and assessments of crown health and survival as well as the presence or absence of sunken bark, gummosis or stem borer infestation were carried out 12 months post inoculation. Narrow-sense heritability estimates were moderate for external variables and for crown health (0.14–0.24) and survival (0.14–0.22). Genetic correlation estimates between trials were generally high, indicating that assessments were repeatable across trials. Correlations between traits used to assess damage following inoculation indicated that different traits may be used to identify clones that tolerate infection. The accuracy of the screening showed that resistant clones can be identified and used to produce A. mangium tolerant to infection by C. manginecans.