Evaluating the inheritance of <i>Ceratocystis acaciivora</i> symptom expression in a diverse <i>Acacia mangium</i> breeding population §

Abstract

A dramatic rise in the incidence of a serious canker and wilt disease of Acacia  mangium has led to the replacement of thousands of hectares of plantation forests in eastern Sabah. A disease screening program was initiated to evaluate levels of disease resistance and tolerance to the causative fungus, Ceratocystis acaciivora, in an A. mangium breeding population. Resistance was evaluated as the presence or absence of external symptoms in two open-pollinated progeny trials. In addition, tolerance was evaluated in one of these trials by measuring the size of lesions produced following a controlled inoculation with C. acaciivora. Heritability estimates were low to moderate for growth traits but were close to zero for the range of traits used to evaluate Ceratocystis resistance and tolerance. Nevertheless, significant differences were found among the three sources (families from the local land race, Queensland and Papua New Guinea origins, all selected in progeny trials in Sabah) and among populations within these sources for many of the traits used to assess damage by the pathogen. Significant differences in lesion length among sources were evident, but no differences among populations within sources were found. Differences among sources and populations would have been reduced as seed was sourced from a progeny within provenance trial where hybridisation among origins and populations would have occurred. Results of this study suggest that modest genetic improvement may be realised from selecting among populations and sources for resistance and tolerance to this pathogen. However, the lack of additive genetic variation will make the development of resistant breeds challenging.

Keywords: Acacia mangium, Ceratocystis, genetic parameters, resistance,  tolerance