GRAFTING OF

ONTO YOUNG SEEDLINGS

Scot C Nelson

Scions of Acacia koa Gray () were grafted onto rootstocks of A. koa, A. mangium Willd., and A. confusa Merr. using cleft or splice grafts applied to very young seedlings. This is the first report of grafting success between A. koa and any Acacia species. Acacia koa scion at the sec- ond true leaf stage of development were joined with the Acacia rootstocks of similar phenology just below the cotyledons. The initial grafting trials resulted in success rates from 20% to 70%. Graft unions were com- pletely healed within 8 wk, and plants were ready for transplanting at about 3 mo. These methods allow for the production of grafted A. koa seedlings with potentially increased disease resistance, improved hor- ticultural performance, and potentially wider adaptation to Hawaiian ecosystems and landscapes.

Nelson SC. 2006. Grafting of Acacia koa Gray onto young Acacia seedlings. Native Plants Journal 7(2):137-140.

KEY WORDS

Acacia koa, Acacia mangium Acacia confusa, cleft grafting, splice grafting, disease resistance, koa wilt

NOMENCLATURE

USDA NRCS (2005)

Photos by SC Nelson

Figure 7. Cleft graft, 2 wk after joining scion (A. koa) with rootstock (A. koa).

137

NATIVEPLANTS I SUMMER 2006 cacia is a genus of about 1300 Grafting onto disease-resistant root- daily. After seed germination, plants species of shrubs and stocks of related species and vari- were inoculated to fix nitrogen with belonging to the subfamily eties is one of the best solutions for aqueous suspensions of crushed Brady- Mimosodeae of the family Faba- managing a number of soilborne plant rhizobium nodules obtained from green- ceae. Koa (Acacia koa Gray) is endemic pests. Although attempts to graft some house cultures growing on each of the 3 to the Hawaiian Islands and is the sec- Acacia species have been successful Acacia species. Acacia seedlings were left ond most abundant overstory species in using various in vivo and in vitro meth- to grow under greenhouse conditions upper elevation forests in Hawail. It ods (Danthu and others 1998; Monteu- until the first 2 sets of true leaves had forms nearly pure stands in montane uis 1995 and 1996; Palma and others emerged, at which point they were used forests, such as those on the slopes of 1996 and 1997), previous attempts to as rootstocks for grafting. Mauna Loa, between approximately graft A. koa—even when using a variety 1230 and 2150 m (4039 and 7095 ft) of approaches—met with failure (Skol- Grafting A. koa onto A. koa (Whitesell 1990). men 1978). A young seedling grafting To obtain scions, seedlings of A. koa Koa is of critical ecological, social, method apparently has not been at the 1 to 2 true leaf stage were decapi- and economic importance to Hawaii. attempted for koa, even though an iden- tated with a scalpel 1 to 2 cm (0.4 to 0.8 Ecologically, koa provides habitat for tical seedling graft method is useful in in) below the cotyledons. At this pheno- numerous native birds, insects, and other other systems such as commercial coffee logical stage, stems were approximately flora and fauna. As a nitrogen-fixing production in Hawail. We believe that 2 to 4 mm (0.08 to 0.16 in) wide. To leguminous species, koa is thought to A. mangium and other Acacia species obtain rootstocks, seedlings of identical account significantly for the nitrogen may possess useful immunity or resist- phenology were decapitated with a content of otherwise nitrogen-poor vol- ance to koa wilt and therefore may be scalpel just below the cotyledons. A lon- canic forest soils (Whitesell 1990). valuable rootstocks if a method for gitudinal split (3 to 6 mm [0.12 to 0.24 Socially, koa is a prominent component grafting them can be developed. in] ) in the stem of the rootstock was of Hawaiian legends and culture. Eco- The objective of this research was to made with the scalpel. The scion's stem nomically, koa is considered the most test the hypothesis that A. koa could be was trimmed to a wedge shape to match valuable of the common native Hawai- grafted successfully onto young seed- the cleft created in the rootstock (Figure ian timber species, valued at about US$ lings of A. koa and other Acacia species 1). The trimmed scion was then inserted 40 per board foot. Koa wood, sometimes by applying a simple cleft- or splice- into the split stem of the rootstock so referred to as "Hawaiian mahogany," can grafting method. If successful, it might that at least part of the cambium layers be highly polished to emphasize its deep allow koa to be grafted and grown suc- of the 2 plants became aligned. A stan- reddish coloration with wavy ("curly") cessfully in the presence of the deadly dard small grafting clip, with pieces of grain and is used for furniture, paneling, and destructive soilborne plant patho- soft foam rubber attached, secured the voyaging canoes, and such woodwork- gens that plague it in Hawaii. graft union (Figure 2). Grafted plants ing crafts as bowls and ukuleles. were placed in a Plexiglas moist cham- A number of significant soilborne ber at room temperature under diffuse, pests, including root-knot nematodes MATERIALS AND METHODS natural light next to a window for 5 to 7 (Meloidogyne spp.) and vascular wilt d, after which the grafting clips were fungi (Gardner 1996), severely affect koa Seeds of A. koa, A. mangium, and A. con- removed. Two wk after clips were in Hawai`i. Of these, koa wilt is probably fusa were collected in 2004 and 2005 from removed, plants were moved to a 60% the most prevalent and devastating dis- plants growing on the island of Hawail. shadehouse and managed for further ease (Anderson and Gardner 1998). Seeds were scarified by hot water (Friday grow. For plants joined by splice grafts, Often fatal to koa, this poorly understood 2000). Distilled water was brought to a the process was similar except that stems disease is believed to be caused by the boil, removed from the heat to cool were cut at rather acute, complementary soilborne fungus Fusarium oxysporum f. slightly, and poured over the seeds. After 2 angles instead of wedges (Figure 3). sp. koae ( Gardner 1980; Anderson and min, the hot water was replaced with cool others 2002), although other factors and distilled water and the seeds were soaked Grafting A. koa onto A. mangium possibly pathogens are implicated in dis- overnight before planting. and A. confusa ease etiology (koa wilt is perhaps a com- Scarified seeds were planted into To join A. koa onto dissimilar Acacia plex of F. solani and F. oxysporum [James seedling trays containing a 3:1:1 mixture species, the same method described above 2006]). The disease is a major threat to of peat, vermiculite, and commercial was used for growing the seedlings, for the cultivation of koa at some locations potting soil. Seedling flats were placed in preparing them as scions, and for grafting. 138 in Hawaii. a 60% shadehouse and watered twice Acacia mangium seedlings, however, had

NATIVEPLANTS I SUMMER 2006 GRAFTING OF ACACIA KOA GRAY ONTO YOUNG ACACIA SEEDLINGS Figure 2. Grafting clips were needed for about 2 wk. Figure 3. Splice graft, 3 wk after joining scion (A. koa) Figure 4. Cleft graft union 8 wk after joining scion (A. with rootstock (A. confusa). koa) and rootstock (A, mangium). to be planted earlier and allowed to healed completely by about 8 wk after could indicate a level of graft incompati- grow 2 mo longer than the A. koa grafting (Figure 4). Plants at 6 mo after bilty that may eventually cause problems seedlings to become large enough to grafting (still in pots) reached a height of at the graft union. Time will tell if the graft match the stem size of A. koa scions of more than 1.5 m (5 ft) (Figure 5). unions are durable—long-term observa- similar phenology. Acacia confusa seeds Plants joined by cleft grafts were tions of grafted plants are needed to ensure were planted at the same time A. koa somewhat sturdier than plants joined by their long-term suitability. Preliminary seeds were planted because they grew splice grafts. Splice-grafted plants data are promising; we have 9-mo-old and developed at similar rates. Cleft tended to become top heavy, leaning grafted plants (one planted outside) that grafts were used primarily to join A. koa over at the point of graft union, and had are taller than 3 in (10 ft) and show no sign and A. mangium. Splice grafts were used to be supported with small wooden of graft union incompatibility. (Figure 6) primarily to join A. koa and A. confusa stakes or toothpicks. Overall, after 9 mo the graft unions because the plants grow at similar rates between A. koa and A. mangium had much as seedlings, the graft unions heal rap- better, seamless graft unions than did idly, and the splice grafts were quicker to DISCUSSION grafts between A. koa and A. confusa. perform. Grafted seedlings were placed The need to grow the A. mangium in humid chambers at room tempera- This is the first report of successful seedlings for 2 mo (or longer) before ture for 1 wk before grafting clips were grafting of A. koa onto A. koa or any using them as rootstocks resulted in removed. Plants were transferred to the other Acacia species. The method stems that were not as tender and were 60% shadehouse 2 wk later for further proved to be quick, relatively inexpen- woodier than A. koa scions. The joining growth and development. sive, and easy to use. of very tender tissue with more woody The margin of error is very small tissue is perhaps another factor that when grafting Acacia seedlings at this reduced the percentage of successful RESULTS stage of growth, because the narrow stem grafts between the 2 species. diameters require very precise alignment Our results suggest that A. koa may Grafting success rates achieved in our of the scion and rootstock, and the young have a wide grafting compatibility with first trials varied among species. The stem tissues are easily damaged. Although Acacia species; we intend to examine the success rate was approximately 70% for grafting was possible, a relatively high use of other Acacia species as rootstocks. A. koa to A. koa grafts and for A. koa to percentage of failed grafts occurred when These grafting methods may be useful to A. confusa grafts. The success rate was grafting A. koa onto A. mangium join dissimilar koa families with various 20% to 25% for A. koa to A. mangium seedlings. Further grafting practice, as horticultural or genetic attributes as well, grafts. The grafting process was very sim- well as determining optimum conditions perhaps allowing adaptation of desirable ple and fairly rapid; a pair of seedlings for holding the plants while the grafts koa families to a wider range of environ- could be joined and clipped together at a heal, may improve the percentage of suc- ments in Hawaii. We were able to graft rate of 2 to 3 min initially and then at 1 cessful grafts. But the difficulty we experi- dissimilar A. koa families from different min or less after practice. Graft unions enced grafting A. koa onto A. mangium islands in this study (data not presented). 139

SCOT C NELSON NATIVEPLANTS I SUMMER 2006 James RL. 2006. Personal communication. Coeur dAlene (ID): USDA Forest Service, State Private Forestry, Forest Health Protection. Plant Pathologist. Monteuuis 0. 1995. In vivo grafting and in vitro micrografting of Acacia mangium: impact or ortet age. Silvae Genetica 44:190-193. Monteuuis 0. 1996. In vitro shoot apex micrografting of mature Acacia mangium. Agroforestry Systems 34:21 3-21 7. Palma B, Vogt G, Neville P. 1996. A combined in vitro/ in vivo method for improved graft- ing of Acacia senegal (L.) Willd. Journal of Horticultural Science 71:379-381. Palma B, Vogt GF, Neville P. 1997. Micro- grafting, an answer to the in vitro multi- plication of Acacia senegal (L.) Willd. Annals of Forest Science 54:203-210. Skolmen RG. 1978. Vegetative propagation of Acacia koa Gray. In: Smith CW, editor. Figure S. Grafted A. koa plant 6 mo after grafting Figure 6. A 13-mo-old A. koa grafted onto a A. Proceedings, second conference in natu- Dnto A. mangium rootstock. mangium. ral sciences; 1978 June 1-3; Hawaii Volca- noes National Park. p 260-273. Nonnative sprouts possibly arising REFERENCES [USDA NRCS] USDA Natural Resources Conser- vation Service. 2005. The PLANTS database, from the rootstock tissue is not an antici- version 3.5. URL: http://plants.usda.gov pated issue because the graft union was Anderson RC, Gardner DE. 1998. Investiga- (accessed 23 Nov 2005). Baton Rouge (LA): made below all meristematic tissues of the tions of koa (Acacia koa) decline in Hawai- National Plant Data Center. ian forests. In: Secretariat for Conser- rootstock (that is, below the cotyledons). Whitesell CD. 1990. Acacia koa Gray. In: Sil- vation Biology, editors. Proceedings of the vics of North America: 2, hardwoods. Hawaii Conservation Conference; 1998 Burns RM, Honkala BH, technical coordi- July 30-31; Honolulu, HI. p 15. CONCLUSION nators. Washington (DC): USDA Forest Anderson RC, Gardner DE, Daehler CC, Service. Agriculture Handbook 654. p Meinzer FC. 2002. Dieback of Acacia koa 17-28. Simple and relatively reliable, these graft- in Hawaii: ecological and pathological ing methods for Acacia koa could be characteristics of affected stands. Forest applied to other species within the genus and Ecology Management 162:273-286. Acacia to provide a disease- or pest-control Danthu P, Sall PN, Seck M. 1998. Grafting tactic with potential for forestry applica- compatibility between some African Aca- tions if the cost to produce grafted trees cias: first results. Bois et Forets des is held low enough to make large-scale Tropiques 258:49-56. production economically feasible. How- Friday JB. 2000. Seed technology for forestry ever, this grafting method should com- in Hawaii. Manoa (HI): University of Hawaii, College of Tropical Agriculture plement, not be a replacement for, other and Human Resources. Cooperative powerful tools for disease mitigation, Extension Service RM-4. 15 p. such as breeding. Gardner DE. 1980. Acacia koa seedling wilt We have immediate plans to test the A. caused by Fusarium oxysporum f. sp. koae, mangium and A. confusa rootstocks f. sp. nov. Phytopathology 70:594-597. against the fungal pathogens in the koa Gardner DE. 1996. Acacia koa: a review of its wilt complex and against root-knot diseases and associated fungi. In: Ferrenti- nematodes. We intend also to examine the nos L, Evans D, editors. Symposium pro- performance of grafted plants trans- ceedings, koa: a decade of growth; 1996 planted into forests or landscapes to Nov 18-19; Honolulu (HI): Hawaii Forest evaulate the long-term compatibility of Industry Association Annual Symposium. the graft union and the vigor of the plants. p 56-63.

NATIVEPLANTS I SUMMER 2006 GRAFTING OF ACACIA KOA GRAY ONTO YOUNG SEEDLINGS