A sampling study of branching characteristics towards obtaining more efficiency for tree selection in breeding trials

[摘要] ENGLISH ABSTRACT:A total of 125 trees covering a range of tree diameters were selected from a progeny trialof open pollinated progenies of Pinus patuia for studies on trait assessments andevaluation for branching characteristics. The trees comprised 25 families with eachfamily having five trees. The trial was 36 months old and was located in a relatively highyielding site in Block B at Usutu in Swaziland. The height, diameter, the number ofbranches and the number of whorls of each tree were recorded. In addition to theseobjective assessments on individual trees, trees were given scores for branch size, branchangle, stem straightness and crown coarseness. For the detailed branch evaluation study,trees were marked at 20% and 50% of the total tree height and the section between thisrange was used. On this section the internode length, the internode diameter, the branchdiameter and the branch angle were measured. It was observed that the objectiveassessments correlated strongly with the scoring (subjective) and it was furtherrecommended that a closer look is needed to consider the prospects of employingsubjective assessments as a means of reducing costs incurred during objective traitassessments. The branch sampling study revealed that there were prospects of assessingfewer branches on a tree as opposed to assessing all the branches, which could be a majorcontributor to the high costs in tree breeding. All three methods used to explore thisprospect showed some reasonable agreement with each other in this regard. The bestsample is to measure all branches in whorl one and two above 20% tree height followedby sampling four branches, two from the first whorl and two from the second whorl.There is a slight difference in these two samples as determined by the coefficents of determination. The study recommends that four branches can be used in the assessmentof the branch angle and the branch diameter on the trees when one considered the costelements.

[发布机构] Stellenbosch University