Crown ideotypes for genetically improved black walnut ( Juglans nigra l.) clones under an intensive management regime in Indiana, USA

Developing crown ideotypes is important for more efficiently producing timber from black walnut (Juglans nigra L.), a valuable hardwood species that mainly grow in the Central Hardwood Region, US. To develop black walnut crown ideotypes for timber growth under an intensive management regime in North-Central Indiana, the following investigations were conducted: ^ 1. Leaf area is strongly correlated to light interception and growth. Mixed effects, allometric models for leaf area and mass at both branch- and tree-level were developed for some genetically improved black walnut clones. Mixed effects branch-level models were built for nine clones. Branch-level model indicated that branches in the top and the base of the live crown grew more leaf mass and area than similar sized branches in the middle of the live crown. Tree-level models were then developed for 25 clones by summing branch-level estimates. Models with crown radius and diameter at breast height (DBH) predicted whole-tree leaf area and mass better than models using DBH alone. Further, there were strong clonal differences in total leaf area, stem volume increment, leaf area index, foliar density index, and growth efficiency. These differences together with the allometirc models demonstrated that some genotypes were more growth efficient in producing bolewood than others. ^ 2. Branching pattern and dynamics are key determinants of tree growth and wood quality. Multi-level, linear mixed effects models of a list of branch attributes were developed for 25 black walnut clones. Branch attributes that were models included: 1) maximum branch diameter in a segment; 2) relative branch diameter in a segment; 3) one-year radial growth of branches; 4) branch insertion angle; 5) first - order branch length; 6) branch frequency; 7) branch basal area per meter of stem. Branch and segment position within a crown were major predictors for branch characteristics, while branch angle also influenced branch allometry. DBH was the most useful tree-level predictor for branch attributes. Desirable characteristics were shown: some clones had small branches or small branch basal area per meter of stem when assuming a same DBH; some clones had large branch angle given a same branch diameter; variance also existed in branch length and branch frequency. These clone variance that captured by the branch allometric models indicated that some black walnut clones had better balance between fast growth and good wood quality, and this balance may also be enhanced through further breeding programs. ^ 3. Estimation of genetic parameters can help improving the efficiency of genotype evaluation and selection process in plant breeding programs. The genetic variation and inheritance of a number of traits in phenology, morphology, physiology, and the genetic correlations among them were investigated for 25 black walnut clones. ^ 4. Microsatellite markers were useful in fingerprinting cultivars and determine genetic relatedness among them. A set of eight microsatellite markers was used to genotype 25 black walnut clones. The identity of 212 ramets was verified, and a few trees among them were found mislabeled. A genetic dendrogram was constructed to show genetic relatedness among clones. In addition to verifying known pedigrees, new discoveries were: clone C55 and C702 were closely related, as well as C705 and C728. Two more dendrograms, one based on crown architecture traits, and the other on tree size and form traits, were also built to compare with the genetic dendrogram. The genetic dendrogram showed that these eight molecular markers had the ability to distinguish genetically related clones from less related ones. Crown architecture traits and tree size and form traits also were able to group genetically related clones together. Based on the investigations on foliage models, crown architecture pattern, and the clonal repeatabilities of, and the genotypic correlations among different traits, a crown ideotype for black walnut grown for timber and another for nuts were developed.