Potential for genetic improvement of yield of exotic softwood tree species in Rwandan plantation forestry
Exotic softwood tree species play a major role in Rwandan plantation forestry. They are used to produce sawn timber used for various purposes. Pinus patula is the major commercial species. Growth and yield of this species were compared in terms of seed source variation based on two trials, one established in Muhanga-Ndiza, Mushubati District, Gitarama Province at 16 years and another in Cyeru District, Ruhengeri Province at 15 years. Yield comparison was also made between P. patula and other new species being tested namely P. caribaea, P. kesiya, P. maximinoi and P. tecunumanii. Although results are variable, it seems that genetic gains are possible in P. patula through the use of appropriate geographic sources. Land races from other African countries may play a major role in establishing a simple breeding strategy based on more seed introductions. Very significant improvements in volume production can be achieved through the use of other promising species such as P. maximinoi and P. tecunumanii. Further testing and improvement may confirm the potential of the two species since the current conclusions were drawn from results from small trials. Further improvements may possibly be achieved by introducing other tropical pine species such as P. oocarpa and also through crossing of related species. Unlike the other pine species, P. kesiya proved to be poorly adapted to local conditions and should not be considered in Rwanda as a plantation tree species. It is recommended that improved germ plasm from external sources be included to accelerate the tree improvement programme for the most promising species in Rwanda.