Leucaena diversifolia - fast growing highland NFT species
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.
BOTANY.
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).
Subspecies.
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.
ECOLOGY.
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.
DISTRIBUTION.
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.
USES.
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.
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.
SILVICULTURE.
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.
HYBRIDS.
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.
PRINCIPLE REFERENCES:
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
