Tropical Fruit Tree Propagation Guide
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Fruit, Nut, and Beverage Crops July 2017 F_N-49 Tropical Fruit Tree Propagation Guide Ken Love1, Robert E. Paull2, Alyssa Cho2,3, and Andrea Kawabata2,4 1Hawaii Tropical Fruit Growers Association, Captain Cook, HI; 2Tropical Plant and Soil Sciences, University of Hawai‘i at Manoa, Honolulu, HI; 3Hilo, HI, 4Kealakekua, HI everal methods can be used to propagate or multiply Asexually propagated trees are clones of the mother tropical fruit trees, including 1) seed, 2) cutting, 3) plant and bear the same type of fruit. The material used micropropagationS or tissue culture, 4) marcottage or air for asexual propagation is normally obtained from a plant layering, and 5) grafting. Propagation by seed is regarded in the adult, not the juvenile, phase. This adult material as the most “natural” method, but frequently the new will have already fruited, so its quality can be evaluated. plants are not identical to the mother plant. Thus physical Trees obtained from adult plants will flower and fruit and genetic variability occurs; new fruit tree varieties and upon receiving an external flower-induction signal and cultivars are created via seedlings. However, asexual or do not need to pass through a juvenile phase as would a clonal reproduction is the preferred method for establish- seedling. If no external stimulus is required for flowering, ing tropical fruit tree orchards and is typically used to an asexually propagated fruit tree will flower immedi- multiply selected varieties and cultivars while ensuring ately. This earlier flowering results in smaller trees, which that the genetics, physical and physiological characteris- can be desirable for ease of harvesting. In the case of tics, and fruit quality remain the same in the mother and grafting or budding, the existence of a graft or bud union daughter trees. Air layering, grafting, and tissue culture can restrict the internal xylem and phloem transport and are the most commonly used techniques for producing additionally influence tree-size reduction and precocity clonal fruit trees. (Paull and Duarte 2011). Dwarfing rootstocks are often sought for species that normally grow very large. Because Differences between sexually and asexually of early flower and fruit development, it is advisable to propagated fruit trees remove the flowers from a newly grafted tree, as the graft Trees originating from seed tend to be vigorous since union cannot take the weight of the fruit. they are in a juvenile state and do not flower or set fruit until they reach a certain age and become mature adult Sexual propagation by seedlings trees. For some fruit trees, the juvenile period can be Many tropical fruit trees flower and fruit annually, and extensive, lasting eight to ten years or more. During their seeds are often recalcitrant. “Recalcitrant” means this juvenile period, the plant will grow vigorously and that the seeds cannot be stored for long periods of time. become very large unless managed and trained with Recalcitrant seeds rapidly lose their viability if allowed pruning. Additionally, seedling trees are naturally ge- to dry, making seed propagation more difficult. As such, netically different from their mother and siblings. As a sowing must be done immediately following fruit harvest. result, seedlings will have different growth patterns and Self-fertilization is less common in tropical fruit trees, produce fruit with different- (usually inferior)-quality which are mostly cross-pollinated with other varieties or characteristics, making marketing difficult (Paull and pollen from male trees. Therefore, seedlings are usually Duarte 2011). very different from the mother tree, as previously men- Published by the College of Tropical Agriculture and Human Resources (CTAHR) and issued in furtherance of Cooperative Extension work, Acts of May 8 and June 30, 1914, in co- operation with the U.S. Department of Agriculture, under the Director/Dean, Cooperative Extension Service/CTAHR, University of Hawai‘i at Mānoa, Honolulu, Hawai‘i 96822. Copyright 2011, University of Hawai‘i. For reproduction and use permission, contact the CTAHR Office of Communication Services, [email protected], 808-956-7036. The university is an equal opportunity/affirmative action institution providing programs and services to the people of Hawai‘i without regard to race, sex, gender identity and expression, age, religion, color, national origin, ancestry, disability, marital status, arrest and court record, sexual orientation, or status as a covered veteran. Find CTAHR publications at www.ctahr.hawaii.edu/freepubs. UH–CTAHR Tropical Fruit Tree Propagation Guide F_N-49 — July 2017 tioned. In some cases, in the absence of fertilization by be budded or grafted (vegetative propagation) and 2) pollen, fruit trees produce apomictic seeds. This situation producing a tree with a taproot for post-planting tree occurs in Garcinia spp. (i.e., mangosteen, achachairu) stability. However, as with seed propagation, rootstock and jaboticaba, where vegetative embryos are present in seedlings are often highly variable, and there is a prefer- the seed but sexual embryos are not. In contrast, mango ence to propagate rootstocks from cuttings or layers so varieties of the Indochina–Philippine group and most that they are genetically identical. citrus species have seed tissues that derive from embryos that are considered clonal and may be used in propagation Asexual or Vegetative Propagation (Paull and Duarte 2011), though this is not a commonly Regenerating or propagating a new plant from a piece used technique in some citrus due inferior root mass. or part of a mother plant is called clonal or vegetative In commercial crop production, the only seed- propagation. Vegetative propagation began being used on propagated plants that are identical to their mother plant woody fruit tree species after it was recognized that seeds are those that have been self-fertilized for many genera- from trees did not breed true to the mother plant. Genetic tions, such as rice and wheat. Fruit trees rarely have this improvement and fruit tree domestication required a level of in-breeding. Fruit that may be propagated by mastery of clonal or vegetative propagation (Zohary and seed are usually herbaceous and short-lived crops like Spiegel-Roy 1975, Mudge et al. 2009). Cloning developed papaya, cocona, naranjilla, tree tomato, yellow and purple around 3,000 to 4,000 BCE in the domestication of figs, passion fruit, giant passion fruit, sweet granadilla, cape grape, promegrate, and olive, which all rooted easily from gooseberry, and some others like coconut and pejibaye cuttings, while date could be propagated from off-shoots palm (Bactris gassipaes) (Paull and Duarte 2011). Vari- (Figure 1). More difficult species such as apples, pears, ability is very low in these crops since the best fruit are and plums that do not root well from cuttings required selected to obtain seed, and selected seed is very similar the development of grafting. Grafting has been used for genetically to the mother plant. However, when they are thousands of years, since about 1,000 BCE, on woody grown in an environment different from where they were perennial tree crops to enhance yield and reduce disease selected, seedlingscan show considerable variation, as (Mudge et al. 2009). Grafting possibly developed from may happen with papaya. the observation that tree limbs of the same species often Besides producing fruit trees of varied genetics and fuse when they cross each other. This method of grafting, physical characteristics, some of the main benefits of refered to as inarching or approach grafting, is still used growing seedlings include 1) obtaining desired rootstock today (Juniper and Maberly 2006). When and where the material onto which the desired variety or cultivar will use of a detached scion was invented is not known. A B C D Figure 1. Propagation through ages: A. Detached-scion grafting from third-century mosaic, Vienne, France (Janick 2005); B. Approach grafting (Nickolson 1884); C. Aerial layering in Japan, early 1600s; D. Grafting by Winslow Homer, Harper’s Weekly, New York 1870. 2 UH–CTAHR Tropical Fruit Tree Propagation Guide F_N-49 — July 2017 Plants can be vegetatively propagated using many occur in these plants. Soft-tissue plants like pineapple, different tissues, including the roots (breadfruit), stems papaya, banana, and plantain are commercially produced (guava), apices (banana), and buds (citrus). Using vegeta- by micropropagation. There has been some success with tive propagation, a large number of nursery plants with avocado, mango, Annonas spp., and jackfruit. The initial the same genetic makeup can be obtained at one time, cost per plant is normally higher than with plants propa- having known tree-growth and fruit-quality characteris- gated using other asexual methods, but the advantage is tics. Vegetative propagation is particularly useful when that many plants can be generated from one mother plant. seed collection is difficult; only juvenile, non-flowering Not all plants within a specific species can be tis- trees are available; or rapid multiplication of selected sue cultured. Musa spp. (banana), for example, has been high-value plants with expected inherited characters is extremely successfully propagated in this way with many desired (Table 1). varieties. However, many but not all of the Hawaiian bananas have so far eluded propagators’ ability to use Cuttings tissue culture. Tropical fruit tree cuttings are typically grown from plant stems and root shoots. Cuttings can be created from ter- Air-layering (marcottage) minal (branch-tip) or sub-terminal (below-the-tip) parts Air-layering, or marcottage, is the most popular layering of a shoot. Basal leaves are removed from sub-terminal system for tropical fruit trees. In this technique, a portion cuttings. If hardwood or semi-hardwood cuttings are of a branch relatively close to the tip and still attached to used, all the leaves are removed, as for Spondias spp. the tree is cinctured (ring-barked) to remove cambial tis- (mombin). Rooting hormones with auxin-like activity sue, after which it is put in contact with a moist substrate are applied to the base of the cutting as a liquid, gel, or or medium (Figure 2).