New leucaenas for southeast Asian, Pacific and Australian agriculture

• Rural Development Bank, Papua New Guinea
• Bureau of Animal Industry, Philippines
• Hanoi University of Science, Vietnam
• University of Technology, Papua New Guinea
• International Center for Tropical Agriculture, Philippines
• Agriculture Western Australia, Australia
• Queensland Department of Primary Industries, Australia
• CSIRO Tropical Agriculture, Australia

The highly productive tree legume leucaena is valuable for supplying high quality forage for cattle. Plantings in northern Australia have demonstrated its drought resistance. In Southeast Asia smallholders use it as a cut-and-carry fodder species and in alley cropping and other agroforestry and landscape stabilisation purposes. It provides fuelwood, paper pulp and organic fertiliser.
However, a psyllid insect, Heteropsylla cubana, caused major problems in 1985 in the Philippines, where it devastated leucaena plantings. Other limitations include low temperature and frost intolerance, intolerance to strongly acid or waterlogged soils, poor seedling vigour, high seed production (causing concern about weediness), and only moderate wood quality for fuelwood and construction purposes.
Lines of leucaena planted around the world originated from a narrow genetic base. Only one of the approximately 16 species of the Leucaena genus, Leucaena leucocephala, had been utilised. Introduction of improved germplasm would increase prospects for using leucaena more widely. Opportunities existed to exploit other species directly or to develop new cultivars through hybridisation between species.
This project was planned at an international workshop on leucaena in Bogor, Indonesia, in 1994, attended by delegates from 21 countries. Research priorities were established, and a steering committee formed the international network (LEUCNET) to promote leucaena research, development and communication.

This project, involving research in Australia, Papua New Guinea, the Philippines and Vietnam, had the following three major objectives:
to identify new cool- and frost-tolerant, acid-soil-tolerant and psyllid-resistant provenances and hybrids of leucaena;
to evaluate and select superior provenances and hybrids for high forage quality;
to select and distribute elite germplasm and disseminate information on leucaena production and use to farmers.

The project built on current research programs in all the collaborating countries. Work included planting about 100 leucaena lines in replicated small plots near Brisbane, and measuring wood and leaf yields and tolerance to cold and psyllid attack. A similar planting was made in the Philippines, and selected lines were planted at 12 diverse sites in the four countries to provide data on environmental response characteristics.
Studies to assess forage quality included feeding trials and chemical analyses. The ability of different Leucaena species and hybrids to promote liveweight gain in livestock was measured in grazing trials in Papua New Guinea and the Philippines.
Elite lines, adapted to a range of environments and with good forage quality characteristics, were selected for propagation in seed orchards. Scientists from the LEUCNET network initiated a pilot extension program.

The key outcome of the germplasm evaluation programs was the identification of the high yield potential and broad adaptation of several L. leucocephala x L. pallida F1 hybrid accessions (designated 'KX2'). These hybrids were the highest yielding accessions in all environments of the multi-site evaluation. Accessions of L. trichandra and L. diversifolia were adapted to low temperatures, with this adaptation most apparent in highland-tropical environments. No accessions were specifically adapted to strongly acid-infertile soils. Accessions of L. leucocephala were highly productive in environments where psyllid pressure was low, but their relative productivity declined rapidly as psyllid pressure increased.
The large differences in psyllid tolerance among accessions of the collection enabled division into four major groupings - highly resistant, moderately resistant, moderately susceptible and highly susceptible. Considerable variation in psyllid resistance was evident among accessions within species of L. trichandra, L. diversifolia, L, pallida and L. collinsii. All L. leucocephala lines were classed as highly susceptible. L. collinsii subsp. collinsii was highly psyllid resistant, had very low condensed tannin content and demonstrated very high in vitro digestibility.
The collaborators established seed production orchards for several elite accessions. So far small quantities of seed have been harvested for distribution or use in subsequent research. Commercial seed production of L. leucocephala cv. Tarramba continues in central Queensland.
Scientists at the University of Queensland developed a method for vegetative propagation of the KX2 F1 hybrid, the most vigorous accession identified in Phase 1, and 6000 rooted cuttings were produced and planted into the field. Propagation techniques were further refined by the Forest Science Institute in Vietnam, where thousands of cuttings are now being propagated. Grafting techniques were also identified that enabled propagation of the KX2 F1 hybrid on both L. pallida and L. leucocephala rootstocks.
In the palatability assessment and ruminant production potential trials, the relative acceptability to grazing cattle of 21 leucaena accessions was high in comparison with three non-leucaena genera (Sesbania, Calliandra and Gliricidia). The most preferred Leucaena species included the L. leucocephala cultivars Tarramba and Cunningham, while the least acceptable species were L. macrophylla and L. trichandra.
The long-term palatability and acceptability of three Leucaena accessions, the KX2 F1 hybrid and its two parents L. leucocephala K636 and L. pallida K748 were evaluated with cattle in Australia and with goats in Vietnam. L. leucocephala was the most palatable species, closely followed by the KX2. L. pallida was of considerably lower palatability and this was reflected in lower milk yields and liveweight gains.
Large-scale grazing trials in the Markham Valley in PNG and on Masbate Island in the Philippines showed that all treatments containing Leucaena improved animal production over grass-only pastures.
Methodologies for the accurate measure of extractable/free condensed tannins (CT) were developed and published. The integration of computer software and spectrophotometer technologies greatly improved the accuracy of the measurement of bound CT. Condensed tannins in the leucaenas generally reduced digestibility of dry matter and nitrogen but all tannins were not equal. There were large differences in the capacity to bind protein among the tannins, and gains to bypass protein from the presence of tannins were often offset by higher losses of endogenous nitrogen.
A study of seasonal variation in CT content of Leucaena spp. revealed significant differences (x5) in CT over a 12-month period. Interactions with growth rate data and climatic parameters were examined. Seasonal variation in CT has ramifications for interpreting published CT data. Cutting the trees (for ease of management) also affected CT status, indicating that defoliation management may be an effective way of manipulating forage quality.
The publication of LEUCNET News has facilitated rapid dissemination of research and development technologies. Seven issues of LEUCNET News were produced over the duration of the project. The editors endeavoured to publish informative articles rather than journal papers.