Leucaena diversifolia (PROSEA)

Plant Resources of South-East Asia Introduction

List of species

Leucaena diversifolia (Schlecht.) Benth.

Protologue: Hook. J. Bot. 4: 417 (1842).

Family: Leguminosae - Mimosoideae

Chromosome number: 2n= 52 (diploid taxa), 104 (tetraploid taxa) (extra chromosomes are common)

Synonyms

• Acacia diversifolia Schlecht. (1838),
• Leucaena laxifolia Urban (1900),
• L. stenocarpa Urban (1900).

Vernacular names

• Leucaena (En)
• Indonesia: lamtoro
• Philippines: ipil-ipil.

Origin and geographic distribution

L. diversifolia is of Central American origin, occurring naturally from eastern and central Mexico through Honduras to Nicaragua. It was introduced into Cameroon, Ivory Coast and Java in the late 1800s. It is now widespread throughout the tropics, particularly in South-East Asia.

Uses

L. diversifolia is primarily used as fuelwood and as a shade tree e.g. in coffee and cocoa plantations in Indonesia and Mexico, and as a green manure. In reforestation schemes, it is planted for soil amelioration and stabilization. In agroforestry and mixed pastures, it is grown as an alternative for L. leucocephala (Lamk) de Wit, where the latter performs poorly because of high altitude or psyllid attack. Sufficiently large logs are used in construction and as poles.

Properties

The wood of L. diversifolia has a density of 400-500 kg/m³, its energy value is 18 900-19 300 kJ/kg. The leaves have a lower digestibility of crude protein than those of L. leucocephala, but this may not affect the total protein uptake. The mimosine content is low (1.5-2.5%). Rations for ruminants should not contain more than 50% L. diversifolia, and the proportion in rations for non-ruminants should not exceed 10%. L. diversifolia produces a water-soluble gum containing the sugar rhamnose.

Botany

• Tree or erect shrub, 3-20 m tall, and with a straight bole up to 40 cm in diameter and slender, ascending branches with horizontal twigs. Bark greyish, lenticellate.
• Leaves bipinnate, 8-25 cm long, with 12-35 pairs of pinnae and up to 4 large glands between basal pairs of pinnae; petiole and rachis reddish; per pinna 20-60 pairs of leaflets; leaflets linear, 3-6 mm × 1-2 mm, apex acute.
• Inflorescence a globose, dense head, 6-15 mm in diameter, reddish, borne in clusters in leaf axil, bearing 50-90 flowers.
• Flower light pink to bright red; calyx 1.5 mm long, corolla 3 mm, stamens 10, 4-7 mm long.
• Pod 10-18 cm × 8-12 mm, bright red, glabrous.
• Mature seed about 5 mm long.

L. diversifolia typically grows as a single-stemmed tree with a straight bole and slender upcurving branches. It nodulates and fixes atmospheric nitrogen with Rhizobium strains that also nodulate with L. leucocephala. On soils very low in nitrogen, a moderate application of N fertilizer may increase nodulation and nitrogen fixation. A fertilizer application of 50-100 kg N/ha was found to increase the number of nodules per tree from 11.5 to 25-30, while nodule dry weight increased by 63-70%.

L. diversifolia is variable in size, adaptation and pubescence, and is subdivided into 2 subspecies: subsp. diversifolia and subsp. stenocarpa (Urban) Zarate (synonym: subsp. trichandra (Zucc.) Pan & Brewbaker). Subsp. diversifolia is tetraploid and occurs wild only in Vera Cruz State in Mexico; it has long leaves, more leaflets per pinna, a longer corolla and pistil, larger pollen grains and larger seed. It is self-compatible, while the diploid subsp. stenocarpa is self-incompatible. Pods of subsp. stenocarpa mature in 80-160 days, those of subsp. diversifolia in about 90 days. Tetraploids are the more commonly cultivated. Cultivars "K156" and "K784" developed in Hawaii are commonly used in agroforestry. The widely used cultivar "KX3" is an interspecific hybrid between L. diversifolia and L. leucocephala.

The taxonomy of Leucaena Bentham is still in flux; the currently recognized 17 species hybridize easily, but hybrids are rare in nature.

Ecology

In the tropics, L. diversifolia grows in areas from 700-2500 m altitude; subsp. diversifolia occurs naturally above 1000 m altitude. L. diversifolia is found in cool and seasonally wet locations with an average annual rainfall of 600-2800 mm and a mean maximum temperature of the hottest month of 18-30 °C. It does not withstand drought well. It has a strong light requirement and tolerates only partial shade. L. diversifolia prefers slightly acid, fertile soils, but is tolerant of leached soils. It is often grown in deforested, degraded areas, dominated by Imperata cylindrica (L.) Raeuschel and Themeda triandra Forssk.

Agronomy

L. diversifolia is propagated by seed. Cuttings and grafts mostly fail, but propagation by tissue culture has been successful. Seed takes about a week to germinate if presoaked in water for 24 hours. The germination rate is generally over 90%. Mechanical scarification and soaking in concentrated sulphuric acid for 5-7 minutes or in hot water (75 °C) for 3 minutes also give good results. Seedling vigour is poor, especially in tetraploid and small-seeded diploid forms. Seedlings reach a height of 15-30 cm in 8-12 weeks and are then transplanted into the field. Application of 15 g of a complete NPK fertilizer (14:14:14) per plant may improve the survival rate of seedlings. L. diversifolia has been tested in intercropping systems e.g. with sweet potato. The total biomass yield of sweet potato, firewood and green manure was considerably greater than the yield per unit area of sweet potato alone.

The annual leaf dry matter production of L. diversifolia can reach 10-16 t/ha. When incorporated as green manure, this adds per ha 72-119 kg N, 2.5-3 kg P, 29-60 kg K, 47-94 kg Ca and 7.5-18.5 kg Mg to the soil. This is equivalent to about 10 t/ha cattle manure per year. Soil erosion can be controlled effectively by planting L. diversifolia. In a trial planting, annual soil loss per ha decreased from 190 t before planting to 54 t in the third year after L. diversifolia had established.

The aggressive nature and profuse growth of L. diversifolia occasionally make it a weed. Seedlings can be controlled effectively by spraying them with diesel oil at the 3-5 leaf stage. Established trees can be controlled by impregnating freshly cut stumps of a basal diameter of 1-20 cm with diesel oil. The treatment should be repeated on coppiced stumps. Delaying application until one day after cutting will reduce its efficacy.

A common disease is leaf spot caused by Camptomeris leucaena. Spots on the upper leaves are often insignificant, but the fungus sporulates profusely, producing crowded black pustules on lower leaves. Fusarium semitectum causes gummosis and canker on stems, branches and peduncles, dark brown spots on young twigs, leaves, peduncles, pods and seeds, eventually causing the tree to die. A moth, Spatularia mimosae, may cause economically significant damage to seeds. Diploid forms of L. diversifolia have a high psyllid resistance, tetraploid forms are only moderately resistant. Diploids and tetraploids show high resistance to seed beetles, Araecerus levipennis and A. fasciculatus; in Hawaii damage to unprotected seed is often only one-quarter of that to seed of susceptible Leucaena species. There are indications that L. diversifolia is tolerant of some root-attacking nematodes.

Genetic resources and breeding

Major germplasm collections are maintained by the Nitrogen Fixing Tree Association (Waimanolo, Hawaii, the United States) and at the Australian Tropical Forage Genetic Resource Centre (Brisbane, Australia), and a smaller collection at the Southern Regional Plant Introduction Station (Griffin, Georgia, the United States). L. diversifolia is important in Leucaena breeding programmes, as it is used as one of the sources of resistance to psyllids and of tolerance to low temperature to be incorporated into L. leucocephala. It easily crosses with nearly all Leucaena species, producing viable hybrids.

Prospects

L. diversifolia is a fast growing, nitrogen-fixing tree, capable of producing high wood and fodder yields and is especially suitable for higher elevations in the tropics.

Literature

• Apigo, R.S., Tumaliuan, B.T. & Tagana, R.M., 1987. Leucaena diversifolia: a possible substitute to L. leucocephala. Canopy International 13(5): 1-2.
• Bray, R.A. & Sorensson, C.T., 1992. Leucaena diversifolia - fast growing highland NFT species. NFT Highlights 92-05. Nitrogen Fixing Tree Association (NFTA), Paia, Hawaii, United States. 2 pp.
• Brewbaker, J.L., 1987. Species in the genus Leucaena. Leucaena Research Reports 7: 6-20.
• MacDicken, K.G. & Brewbaker, J.L., 1988. Growth rates of 5 tropical leguminous fuelwood species. Journal of Tropical Forest Science 1: 83-91.
• Pan, F.J., 1988. Comparison of diploid and tetraploid Leucaena diversifolia. Quarterly Journal of Chinese Forestry 21: 89-98.
• Sorensson, C.T. & Brewbaker, J.L., 1994. Interspecific compatibility among 15 Leucaena species via artificial hybridization. American Journal of Botany 8: 240-247.
• Zarate, S.P., 1984. Taxonomic revision of the genus Leucaena Benth. from Mexico. Bulletin of the International Group for the Study of the Mimosoideae 12: 24-34.

Authors

• I.B. Ipor