Applied disease screening and selection program for resistance to vascular wilt in Hawaiian <i>Acacia koa</i> §

Abstract

Acacia koa is a valuable tree species economically, ecologically and culturally in Hawai’i. A vascular wilt disease of A. koa resulting from infection by the fungal pathogen Fusarium oxysporum f. sp. koae (FOXY) causes high rates of mortality in field plantings and threatens native A. koa forests in Hawai’i. Landowners are  reluctant to consider A. koa for reforestation and restoration in many areas due to the threat of FOXY. Producing seeds or propagules with genetic resistance to FOXY is vital to successful A. koa reforestation and restoration. Virulent FOXY isolates were used in seedling inoculation trials to evaluate resistance levels among A. koa families in greenhouse experiments. Seedling survival varied by family, ranging from 3% to 92%, with an overall average of 46%. One clonal and three seedling field trials were established in 2012 and 2013 using selected families based on the inoculation trials. The greenhouse screening method serves as a powerful tool to rapidly evaluate A. koa families prior to outplanting, but the field trial data are needed to further validate the results and to monitor the durability over time. The field trials will also serve as a source of germplasm for selection of other commercial traits.

Keyword: Acacia koa, disease resistance, Fusarium wilt, seedling inoculation, tree improvement