n Southern African Forestry Journal - Genetic improvement of using breeding seedling orchards and the multiple population breeding strategy in Zimbabwe : scientific paper




<I>Eucalyptus grandis&lt;/I&gt; is commercially important in Zimbabwe and a breeding program has been in progress since 1962. A classical breeding strategy was used initially but, in 1981, the Multiple Population Breeding Strategy (MPBS) was implemented and the concept of the Breeding Seedling Orchard (BSO) became central to the MPBS in Zimbabwe. Two-year height data from five BSOs established at Mtao and Mukandi in Zimbabwe over two successive generations under the MPBS were used to determine the extent of genetic gain and the implications for future breeding strategy. Four genetic checks, three of which were common to all BSOs, were included by which to monitor the possible onset of inbreeding and against which to measure genetic gain. Significant differences between families were detected for height in the third generation BSOs but no significant differences were detected in one-fourth generation BSO. Genetic checks had average ranking at Mtao where they were selected but had very low ranking at Mukandi. Ranking among genetic checks was fairly similar in the BSOs at Mtao, suggesting that the design of the BSOs is satisfactory for producing a ranking of families at two years at this site. However ranking among the genetic checks at Mtao differed from those at Mukandi. Genetic correlation between height at two years and volume at age five years was favorable (0, 81) suggesting that height at two years is a good predictor of volume at five years. There was no genetic progress in second year height in the fourth generation compared to third generation BSOs. To ensure gain in advanced BSOs, larger numbers of families should be included in the BSOs and a Best Linear Unbiased Prediction methodology should be used for selecting candidates for advanced breeding.


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