Leucaena leucocephala is the most likely planted MPT in the tropics. Its successful utilisation, however, has been hampered by a lack of genetic diversity within the species leading to problems of environmental adaptability and, of most concern, attack from defoliating psyllid, Heteropsylla cubana. This pest originates in Central America, but since 1983 has spread across the Pacific and Asia causing severe damage to L. leucocephala. In 1992 the psyllid arrived in mainland Africa, where it is currently found in Burundi, Ethiopia, Kenya, Malawi, Mozambique, Tanzania, Uganda Zambia and Zimbabwe. It can be expected to spread to all countries in Africa where leucaena is grown within the next few years.

Germplasm of multipurpose tree species secured and improved, to develop an integrated approach to overcoming the constraint to productivity caused by the psyllid.

• Family-based seed collections of calothyrsus provenances identified as having superior growth performance will be incorporated into improvement work.
• Knowledge of the species reproductive biology, pollination system and patterns of gene flow will allow optimisation of seed orchard design, which, in turn may overcome problems of seed production in countries as Kenya.
• The extent of interspecific hybridisation within natural populations will have been investigated, and its potential for tree improvement assessed.
• A rational conservation strategy for Calliandra will have been produced.