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Genetic control of fifth year traits in Pinus patula Schiede and Deppe



Genetic control of fifth year traits in Pinus patula Schiede and Deppe



Silvae Genetica 41(4-5): 242-248



Polycross, factorial and diallel mating designs were used in the genetic improvement programme for Pinus patula Schiede and Deppe in Zimbabwe. Their function was to elucidate genetic structure and control in economically important traits, to investigate genotype-environment interaction, to identify the best general combiners and to provide information on the efficiency of mating and experimental designs. Productivity, stem straightness and crown traits were measured in the fifth year from planting in the field. Analysis of the data showed that all traits were under multigenic control with practically insignificant contributions from dominance, maternal or reciprocal effects. Family heritability estimates were highest for the branch traits (up to 0.85, 0.80, 0.91 and 0.91 for branch basal area, total number and number per whorl and internode length respectively) but also high for stem volume (up to 0.82) and moderate for stem straightness (up to 0.67). Genotype-environment (locality) interaction could be of practical value for stem volume but was absent for stem straightness and the branch traits. There was no genotype-year interaction. Sub-blocking made no practical contribution to the precision of ranking the families but use of the lattice design might mean that the same precision of comparison could be achieved for some traits in some environments with experimental plantings that were up to 25% smaller. The assumption of half-sib relationship within families in the polycross was shown to be valid and the test was an efficient one to rank parents for general combining ability. The only adverse genetic correlation was a positive one between the amount of sinuosity in the upper stem in the second year and stem volume in the fifth hear. Otherwise there were very strong genetic correlations between height and diameter in the second year and the same traits in the fifth year (0.94 (s.e. 0.06) and 0.94 (s.e. 0.09) respectively); and the same applied to the branch traits, internode length and total number of branches (0.85 (s.e. 0.11) and 0.91 (s.e. 0.06) respectively). The conclusion is that in the fifth year after planting, there are still strong indications that substantial and rapid genetic gain should be available for P. patula through early selection for general combining ability using conventional breeding methods.

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Accession: 002390540

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