Koa (Acacia koa) is endemic to the Hawaiian Islands that is one of abundant species in the Hawai'i. Koa provide ecological functions that form habitat of numerous native birds, insects, and other flora as an endemic tree. Also, koa support for the nitrogen content of nitrogen-poor volcanic forest soils. Also, koa represent in Hawaiian culture that considered the most valuable of the common native species. A number of diseases of koa caused by pathogenic fungi have been described. Especially, Koa wilt disease is typically virulent on all developmental stages of the host that showed rapid, irreversible wilting and decline because pathogenic fungi are systemically invaded in to the vascular system and contained within internal tissues. Koa in Hawaiian Islands have been shown to be infected with some species of the vascular fungus such as Fusarium oxysporum that is widely present in the soil. Other Fusarium species also isolated from koa such as F. semitectum , F. subglutinans, F. lateritium, F. graminearum, F. proliferatum, F. equiseti and F. solani. The aim of the present research is to isolate and to identify unknown pathogenic fungi in Acacia koa from Hawaiian Islands, and to compare koa seedling that inoculate koa seeds with unknown pathogenic fungal species to monitor the growth rate of koa which species is the most infected to koa.
• Acacia koa is an endemic species and one of the most popular trees in Hawai‘i.
• In Hawaiʻian culture, koa plants considered the most valuable of the
common native species.
• A number of diseases of koa caused by fungi have been described.
• Especially, koa wilt disease is highly virulent on all developmental stages of
• Koa have been shown to be infected with some species of the vascular fungus
such as Fusarium oxysporum.
Fig. 1. Symptom of koa wilt
Objectives of the study
1. Compare koa seed A and B that inoculated with two different Fusarium sp.
: F. oxysporum and F. solani
2. Monitor which Fusarium sp. is the most infected to koa
• Seedling Koa
- Seeds for two groups (A and B) were treated in boiled water until the water cooled (3 controls and 7 treatments).
- F. oxysporum and F. solani were cultured and prepared 10 mL of each stock spores added into each koa plant and provided water after 24 hours
(F. oxysporum : 1 x 105 spore/ml, F. solani : 1 x 106 spore/ml)
• Monitoring growth rate
- The growth rate of koa plants were measured by the height of each koa (mm) every 7days during 8 weeks
- If any koa plants showed the symptom of koa wilt, dark colored stem and root rot were dissected and incubated on water agar (WA)
- After incubated Fusarium spp. on WA, cut a single tip of hypea and move to incubate on vegetable agar.
- For morphological identification, Fusarium spp. were examined by microscopical characteristics.
Fig 2. Planted koa A and B which were inoculated with F. oxysporum and F. solani during 8 weeks.
• The symptom of koa wilt from koa developed after 28 days.
• The parts of dark staining stem and root were isolated and cultured on WA
• A single cell of F. oxysporum from koa A
Fig. 3. The symptom of koa wilt showed after 4 weeks (right). The parts of dark staining of stem and root were isolated on WA. Chlamydospores from F. oxysporum showed a single cell (left).
Fig. 4. Comparison of the growth (mm) for Koa seed A during 8 weeks. The seeds were inoculated by F. oxysporum (5 x 105 cell/ml). Sample numbers indicate the treatments from 1 to 7, the control from 8 to 10.
Fig. 5. Comparison of the growth (mm) for Koa seed B during 9 weeks. The seeds were inoculated by F. solani (1 x 106 cell/ml). Sample numbers indicate the treatments from 1 to 7, the control from 8 to 10.
• F. oxysporum affected to the growth rate and killed 30 % of koa plants in group A.
• F. solani was not affect to the growth rate of koa plants in group B.
• F. solani is not considered pathogenic fungus to koa that based on the results of growth rate from koa.
• The effects of other Fusarium sp. in Acasia koa are not yet known.
• Further researches of other Fusarium sp. for Acasia koa are seriously required.
• Compare the effects of other isolated Fusarium sp. from koa
: F. semitectum, F. subglutinans, F. lateritium, F. graminearum,
F. proliferatum, and F. equiseti