The utility of the predictive decapitation test as a tool for early genetic selection for Hypsipyla tolerance in big-leaf mahogany (Swietenia macrophylla King)

The plantation silviculture of mahogany (Swietenia spp.) has been severely limited by the attack of the mahogany shoot borer (Hypsipyla spp.), which greatly reduces or nullifies the commercial timber value of attacked trees by causing forking low on the stem. Selection for resistance, including tolerance (the capacity to retain apical dominance after attack), is widely considered to have potential as one element in an integrated pest management system. It has been suggested that the response of young seedlings to a predictive decapitation test might be useful as a means of detecting genotypes with high tolerance. This paper describes a pilot provenance/progeny experiment aimed at exploring this hypothesis. The number of shoots produced in response to attacks in the first year of field growth by Costa Rican material was found to be significantly correlated with response to decapitation in the nursery, on both individual tree and family mean bases. It appears, therefore, that the decapitation test could have a role in early selection for tolerance of Hypsipyla in mahogany. However, the presence of within-provenance genetic variation in response to Hypsipyla attack was not established.