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Leucaena diversifolia is the second-best known species in the genus Leucaena. Through numerous international tree trials, it has gained a reputation for aggressive growth at cool or high elevation sites where L. Ieucocephala performs poorly. It is a common companion tree to coffee in much of Indonesia and Mexico. L. diversifolia has moderate or high resistance to both psyllids and seed beetles, and is low in mimosine. Its forage digestibility is somewhat lower than L. Ieucocephala. It produces straight boles, and is desirable for paper and charcoal production.
L. diversifolia (Schlecht.) Bentham (Leguminosae, subfamily Mimosoideae) is a mediumsized tree, often growing 10 to 20 m in height and 10 to 40 cm in diameter. L. diversifolia typically grows as a single stem tree with a long straight bole and slender uplifted branches that terminate in horizontal twigs. Some diploids produce branches at 180 degrees to each other, giving the trees a planar or two-dimensional appearance.
Leucaena diversifolia ssp. diversifolia (Dr. Diane Ragone 1984).
The leaves of L. diversifolia are easily distinguished from L. Ieucocephala by high numbers of small leaflets. The leaflets are 1 to 2 mm wide and nearly 1 cm long. The apex of the leaflet is usually off-center and pointed Flower heads are borne in clusters at leaf axils and average under 1 cm diameter (0.51.8 cm) on the day before flowering. Unlike L. Ieucocephala flowers, the styles of L. diversifolia extend past the anther halo. Flowering is profuse, beginning in late spring and continuing until mid-fall. Flower color ranges from bright red to light pink. Young pods can turn bright red in the sun, accounting for the Mexican name "guaje rojo" or red leucaena (Brewbaker 1987b).
L diversifolia contains two subspecies. The most widely cultivated, L. diversifolia ssp. diversifolia, is line L Ieucocephala being self-fertile and "tetraploid" (2n=104). It is often abbreviated DIV4. The other subspecies, L. diversifolia ssp. trichandra (syn. L d ssp. stenocarpa) is outcrossing and has half as many chromosomes ("diploid"). It is abbreviated DIV2. The subspecific division is important as the breeding methods used to improve each subspecies are very different.
DIV4 pods mature in about 90 days, while those of DIV2 mature in 80 to 160 days. L. diversifolia seed weigh about one third (about 20 seeds/gram) of L. Ieucocephala seed. Seeds of the DIV2 are commonly smaller than those of DIV4.
Unlike L. Ieucocephala, which frequents hot mesic lowlands (sea level to 1000 m), L. diversifolia colonizes higher (700 to 2500 m), cooler, and seasonally wetter sites. Its performance in highland trials is predictably good. Biomass yields of L. diversifolia (DIV4) were five times that of L. Ieucocephala at Mealani, Hawaii 850 m elevation, mean average temperature 18°C (Brewbaker et al. 1988). An Indonesian L. diversifolia diploid performed better than several L. Ieucocephala in Papua, New Guinea (Bray et al. 1988)
L. diversifolia is not frost tolerant. Early indications suggest that L. diversifolia is drought-sensitive. It performs best on fertile (maize-growing) soils, but also colonizes infertile ones. The species is not normally found on acid soils but some can tolerate moderate acidity (Hutton 1984). Some diploids have been discovered growing among pines near Siguatepeque, Honduras. The species does not appear to be tolerant of saline or sodic soils. It tolerates partial shade and seasonally heavy rain.
The native distribution extends from Eastern and Central Mexico (Veracruz and Puebla) south through Guatemala, Honduras and into Nicaragua. The tetraploid is native only in a small region of central Veracruz, Mexico near Jalapa. No diploids grow in this area, although they probably occur in southern Veracruz. The center of diversity of the diploids is Guatemala. Oaxacan (Mexico) diploids are different in tree form (shrubby), pollen (large) and pubescence heavier) from their Guatemalan kin, and may withstand periodic drought.
The naturalized distribution of the species includes the Caribbean, Africa and S.E. Asia. The tetraploid was probably established in Jamaica early in this century. Diploids (probably Guatemalan) were brought into the Ivory Coast, Cameroon and Java, Indonesia in the late 1800s. The Indonesian populations appear to be agronomically superior and may be partially inbred; if so they could be invaluable in hybrid seed production.
L. diversifolia does not have a history of cropping and much of the information on its value remains anecdotal. The primary uses of L. diversifolia are fuelwood, posts, pulpwood, shade and reforestation. It is also used for soil improvement and stabilization, alley cropping and agroforestry, pasture improvement and forage.
In one study, foliar digestibility of L. diversifolia lines were 10-20% less than that of L. Ieucocephala. The higher tannin content of the foliage may increase bypass protein levels in ruminants. Bypass protein is important to ruminants because the protein is protected from degradation in the rumen, but available for absorption in the small intestine, which is metabolically efficient. Mimosine content (1.5-2.5%) is about half that of L. Ieucocephala (4%). Levels of more than 50% of the forage in animal diets are not recommended.
Seed can be scarified by, a 5-7 minute soak in concentrated sulfuric acid, a 3 minute soak in 75°C hot water, or mechanical scarification. L. diversifolia fixes nitrogen with Rhizabium, and has a specificity comparable to that of L. Ieucocephala. Little is known about its mycorrhizal needs; these are also assumed to be comparable to that of L. Ieucocephala.
Seedling vigor of L. diversifolia is poor, especially of the tetraploids and small-seeded diploids (Sorensson et al. in submission?. Seeds may take a week to fully vigorous leucaenas. Seedlings are typically transplanted into the field eight to twelve weeks after germination, when they should be 15 to 30 cm tall. Vegetative propagation from cuttings and grafts has generally failed although tissue culture is successful.
PESTS & DISEASES.
L. diversifolia are generally resistant to insect pests in the field. Tetraploids show moderate psyllid resistance, but defoliate during heavy pest outbreaks (Brewbaker 1987a, Bray and Woodroffe 1988). Some diploids are extremely resistant to psyllids.
Both tetraploids and diploids show high resistance to seed beetles Araecerus levipennis and A. fasciculatus (Braze 1988). Damage to unprotected seed from A. Ievipennis in Hawaii is often one-quarter that to seed of other susceptible leucaenas.
Most interspecific combinations between and within L. diversifolia and other species are successful (Pan 1985, Sorensson and Brewbaker in submission). The best known hybrid is that between tetraploid L. diversifolia and L. Ieucocephala. It is called 'KX3'. It has a broader genetic base than either parent and often outyields them. Like the parents, the hybrid is self-fertile and seedy.
Bray, R.A. and T.D. Woodroffe. 1988. Resistance of some Leucaena species to the leucaena psyllid. Tropical Grasslands 22:11-16.
Bray, R. A., D.G. Cooksley, T.J. Hall and D. Ratcliff. 1988. Performance of fourteen Leucaena lines at five sites in Queensland. Australian J. of Experimental Agriculture 28:69-72.
Braza, R.D. 1988. Two insect pests of L. diversifolia seeds in Surigao del Sur, Philippines. Leucaena Research Reports 9:88-89.
Brewbaker, J.L. 1987a. Leucaena: A multipurpose tree genus for tropical agroforestry. pp 289-324. In: Agroforestry A decade of development. Editors: HA. Steppler and P.K.R. Nair. ICRAFT. Nairobi, Kenya.
Brewbaker, J.L. 1987b. Guide to the systematics of the genus Leucaena (Mimosoideae). Leucaena Research Reports 7(2):6-20.
Brewbaker, J.L., R.W. Wheeler and C.T. Sorensson. 1988. Psyllid-tolerant highland leucaena yields. Leucaena Research Reports 9:11-13.
Hutton, E.M. 1984. Breeding and selecting Leucaena for acid tropical soils. Pesquisa Agropecuaria Brasilia 19 (special issue):263-274.
Pan, F.J. 1985. Relationships within the L. diversifolia complex Dissertation, Univ. of Hawaii. 297pp.
Sorensson, C.T. and J.L. Brewbaker. Interspecific compatibility among fifteen Leucaena species. Submitted to American J. of Botany.
Sorensson, C.T., H.M. Shelton, M.T. Austin and J.L. Brewbaker. Seedling vigor of Leucaena leucocephala, L. diversifolia, L. pallida and their hybrids. Submitted to Tropical Grasslands.
NFTA 90-01 May 1990