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Conserving Leucaena ssp. Germplasm collection

Project start date: 31 March 2012
Project end date: 01 May 2017
Publication date: 30 April 2017
Project status: Completed
Livestock species: Sheep, Lamb, Grassfed cattle
Relevant regions: National
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Pastures of the tropical forage tree legume leucaena (Leucaena leucocephala) are the most productive, profitable and sustainable pastures available to graziers in northern Australia. Graziers are adopting this pasture system with over 200,000 ha established at present. Whilst the leucaena pasture technology has been largely developed in Australia by CSIRO, QDAF and The University of Queensland (UQ), Professor James Brewbaker at the University of Hawaii (UH) is the pre-eminent plant breeder who has worked on the Leucaena genus of tropical forage tree legumes for over 50 years. The objective of this study was to import unique Leucaena germplasm from UH and to collect seed to provide long term benefit to the Australian Leucaena industry by providing accessions that can be used in plant breeding programs to develop novel traits like cold tolerance, psyllid resistance and sterility.

Eighty-seven (87) superior accessions of a diverse array of Leucaena taxa, some recently delineated by botanists, were selected from the UH collection (and other sources) based upon physical inspection of representative plants in existing arboreta, published and unpublished (theses) trial results and original plant collection notes that described the populations of trees from which the seed was collected in Central America.

In September 2008 a Leucaena germplasm orchard of 87 taxa was established at Redlands Research Station, Cleveland QLD. Controlled pollination of the taxa in this orchard was not possible for a number of reasons including, (i) the wide variation in flowering of the taxa meant that constant monitoring on a daily bases was required to capture all the opportunities to carry out the pollinations. This was not possible given the limited human resources allocated to this project, (ii) some taxa did not flower or rarely flowered. The lack of flowering of some accessions may have resulted from the absence of photo-temperature queues that stimulate flowering (iii) some taxa were outcompeted because of their small stature. Some of these taxa still have value as parents in hybrid combination to make sterile triploids e.g. L. greggii and L. retusa (iv) some taxa did not recover well from the original coppice treatment. However, these taxa have been given a better opportunity of healthy growth by removing nearby competing trees.

Over a five year (2012-2017) period seeds were collected from 61/87 taxa planted. Seeds were successfully collected from all the self-compatible tetraploid (4X=104 or 112 chromosomes) species grown in the orchard including L. leucocephala, L. pallida, L. confertiflora and L. diversifolia.  Seed collection from the self-incompatible diploid (2X=52 or 56 chromosomes) species was more problematic.

All 87 taxa have been retained and the orchard can be used for future seed collection opportunities and breeding programs. To this end the trees have been thinned and coppiced to facilitate greater accessibility for those working the orchard. This orchard will now provide a core resource for the development of sterile leucaena by providing diploid and tetraploid taxa that can be inter-crossed to make sterile triploids.

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Primary researcher: University of Queensland