‘KX4-Hawaii’ is a tropical, seedless, multipurpose legume tree developed at the College of Tropical Agriculture and Human Resources of the University of Hawaii. It represents a sterile triploid hybrid between Leucaena leucocephala (Lam.) de Wit ssp. glabrata (Rose) S. Zárate (2n = 104) and L. esculenta (Mociño et Sesse ex DC) Benth. (2n = 52). ‘KX4-Hawaii’ is a rapidly growing tree to 15 m in five years. Its evergreen canopy is open and it has proved to be attractive as an ornamental, windbreak, and shade tree. It has potential also for use as a coppiceable, high-value hardwood grown on eight- to 12-year rotations. It is normally single-stemmed with major branches arising at 3 m or higher. It can be coppiced to create a multistemmed tree for biofuel and is readily cloned. It has been grown at many locations throughout Hawaii, showing high drought tolerance and wide environmental adaptability. It has no known pests or diseases.
Several of the 22 recognized species in the New World genus Leucaena (Hughes, 1997) are grown as shade or ornamental trees. Two species are widely cultivated internationally, L. leucocephala (Lam) de Wit and L. diversifolia (Schlecht) Benth. Both are recognized as shade or support trees for crops like coffee, cacao, pepper, and quinine, and both are self-seeding polyploids (2n = 104). Leucaena leucocephala ssp. glabrata (formerly known as L. glabrata Rose) is the widely grown multipurpose subspecies that is highly valued for timber, fuelwood, fodder, food, and green manure (Anon., 1977; Shelton and Brewbaker, 1994). Significant cultivars bred in Hawaii include K8 (Brewbaker, 1975) and K636, marketed as “Tarramba” (Dalzell et al., 2006). New hybrids such as ‘KX2-Hawaii’ have been bred to be largely self-sterile, similar to most species of the genus (Brewbaker, 2008). Self-seediness is associated with invasiveness and can greatly reduce wood and fodder yields of tropical legumes. These facts encouraged our extensive evaluations of the 12 major seedless hybrids in the genus we have created in Hawaii (Gonzalez et al., 1967; Pan and Brewbaker, 1988; Sorensson and Brewbaker, 1994).
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