Nursery Disease Notes Usda Forest Service Northern Region Forest Health Protection

Nine different Fusarium species were isolated from Acacia koa seeds, seedpods, seedling stem and root tissues, rhizosphere soil and soil surrounding roots of diseased trees. Fusarium oxysporum, the cause of koa dieback and wilt, was not isolated from seeds or seedpods but was found most commonly on roots and soil near diseased koa seedlings. Fusarium subglutinans was the most common species isolated from seedpods, which had evidence of extensive insect predation. Other Fusarium spp. commonly isolated from seedlings and adjacent soil included F. semitectum, F. equiseti, and F. solani. Species isolated less frequently included F. avenaceum, F. acuminatum, F. sambucinum, and F. sporotrichioides. This work indicated that several Fusarium spp., in addition to F. oxysporum, may be common colonizers of diseased koa trees and seedlings. Further elucidation of their role in disease etiology is warranted.