RESEARCH AND EXTENSION | KOA (ACACIA KOA)
Screening of Acacia koa germplasms for resistance to koa wilt
Koa (Acacia koa Gray) is a keystone species in Hawaii’s forests, valued for its ecological significance and high-quality timber. Infection with koa wilt, caused by Fusarium oxysporum f. sp. koae, has resulted in high mortality rates in both field plantings and native forests. Screening for germplasm with natural resistance to koa wilt is critical to support successful koa reforestation and restoration efforts.
This project is being conducted in collaboration with Nick Dudley and his team at the Hawai'i Agriculture Research Center (HARC).
Background
Koa wilt is caused by Fusarium oxysporum f. sp. koae (FOXY), a soil-borne fungus that invades plants through their root systems (Dudley et al., 2007). Once inside the plant, FOXY colonizes the vascular tissue, producing toxins that block water transport to leaves and other above-ground parts of the tree. Symptoms of infection include wilting, dieback, chlorosis (yellowing) of leaves, defoliation, stem necrosis, vascular discoloration, and eventual plant collapse (Dudley et al., 2015). In severe cases, infected trees die within weeks or months. The disease is particularly devastating in area where environmental conditions favor fungal growth and spread. High humidity, warm temperatures, and poorly drained soils create ideal conditions for FOXY proliferation. Additionally, FOXY can persist in soil for extended periods as dormant spores, making eradication difficult (Dudley et al., 2015).
Healthy and wilted koa trees side by side
Vascular discoloration
Importance of Resistance Screening
Given the challenges posed by FOXY's persistence and virulence, identifying resistant koa genotypes is critical for managing koa wilt. The ongoing resistance screening involves testing koa lines under controlled conditions to determine their susceptibility to infection. Resistant families can then be propagated for use in reforestation projects and seed orchards which is the broader goal of sustaining and conserving native forest in Hawaii by prioritizing disease-resistant germplasms.
References
Dudley, N.S., James, R.L., Sniezko, R.A., and Yeh, A. 2007. Investigating koa wilt and dieback in Hawaii: pathogenicity of Fusarium species on Acacia koa seedlings. Native Plants Journal 8:259-266.
Dudley N.S., Jones, T.C., James, R.L., Sniezko, R.A., Cannon, P., and Borthakur, D. 2015. Applied disease screening and selection program for resistance to vascular wilt in Hawaiian Acacia koa. Southern Forests: a Journal of Forest Science 77: 65-73.