MITIGATION OF AN EXISTING AND IDENTIFICATION OF AN EMERGING FUNGAL DISEASE OF KOA

Abstract

Koa (Acacia koa) is a culturally, ecologically, and economically important forest tree of Hawaii. Koa wilt and dieback disease caused by Fusarium oxysporum has been a continuing challenge to the reforestation of former agricultural lands with koa. Koa breeding for disease resistance has identified some individuals useful as parents for disease resistance breeding. Anthracnose disease is a cause for the failure of the production of hybrid seeds in the breeding program. In this study, I have used families derived from five parents (E, F, G, H, and I) that thrived in a lower elevation as parents in diallel crosses and have evaluated the disease severity of the hybrid seedlings under disease treatment. Parent ‘I’ appeared to be superior in delivering disease resistance to offspring, parents ‘E’ and ‘F’ appeared to be intermediate in resistance, and parent ‘G’ appeared to contribute disease susceptibility to offspring. The expression of three chitinase genes, Akchit1a, AkchitII, and Akchit III, was determined using Reverse Transcription PCR. No correlation was found between gene expression and disease severity, indicating that Chitinase is a poor candidate for a disease resistance marker in koa breeding. Finally, both morphological and phylogenetic approaches were used to identify a previously unidentified pathogen that can cause anthracnose on koa. Both morphological and phylogenetic studies showed the fungus as a member of the Colletotrichum acutatum complex; this provides information on ways to control the fungus using specific and general fungicides.