Zimbabwe has a very advanced genetic improvement programme of exotic species of pines and eucalypts. Since the mid 1980's, programmes for other indigenous species (acacias and indigenous fruit trees) and exotic multipurpose species have been initiated. These programmes concentrated on provenance and progeny testing for adaptation and growth of "new" species.
Genetic improvement of exotic timber species for plantation development began in 1958. Since then, dozens of pine species from the southeastern United States of America, Mexico and central America and from Asia were introduced and tested for adaptation, growth and timber qualities. The successful species include Pinus patula, Pinus taeda. Pinus elliottii and Pinus kesiya. Breeding and selection of these species were initiated and today their selected populations are in the third generation of selection and supplying genetically superior clonal orchard grade seed of world reputation. Other potential Pinus spp. being tested are Pinus tecunumanii, P. maximinoi, P. hererrai and P. greggii. Breeding and selection has also been practiced on eucalypts and currently the most advanced breeding populations of Eucalyptus grandis are in the fourth generation of selection. Although dozens of eucalypts have been tested, the most successful species are Eucalyptus grandis, E. cloeziana, E. camaldulensis and E. tereticornis. There has been limited provenance testing of other exotic species such as Liquidambar styraciflua and Acacia mearnsii.
The breeding strategies of all the successful species in Zimbabwe combine selection of desired attributes and gene conservation.
The programme for indigenous species can best be described as simple provenance and sometimes family evaluation. No selection for development of second generation populations has been practised on all the species. The acacias being evaluated are Acacia erioloba, A. nilotica, A. karroo, A. senegal and A. albida. The species are being evaluated for gum arabic production (A. karroo and A. senegal) as well as for browse and pod production for fodder. The indigenous fruit tree species that are being evaluated are Sclerocarya birrea, Uapaca kirkiana and Strychnos cocculoides. Provenance and progeny trials of Uapaca kirkiana have already been established in the field while tests of Sclerocarya birrea are still in the nursery and are expected to be established in the field in December 1999. Germplasm of Strychnos cocculoides has already been assembled while that of Ziziphus mauritiana, a naturalized species, is still to be assembled. Phenological studies of Pterocarpus angolensis have been carried out in natural stands in the demarcated forests. Preliminary genetic variation studies using morphological nursery traits have also been done in Pterocarpus angolensis and Colophospermum mopane.
