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.