Colonization of Hawaiian Acacia Koa Seedlings with Fusarium Species

Acacia koa seedlings were evaluated from plantings and commercial nurseries for colonization by Fusarium spp., particularly F. oxysporum, the putative cause of koa wilt/dieback disease in Hawaii. We sampled 162 seedlings, 90% of which were from nurseries on the islands of Hawaii, Maui, Kauai, and Oahu. Fusarium oxysporum was detected on about 78% of sampled seedlings. It was most prevalent on roots; more than 50% of all sampled root pieces were colonized by this species. Ten additional Fusarium species were isolated from seedlings, but all colonized plant tissues at much lower levels. More than 70% of all samples from seedlings yielded Fusarium spp. The potential importance of this high level of colonization is discussed.