A comparison of rooting ability of stem cuttings made from hypocotyls and epicotyls from 50‐day‐old seedlings of loblolly pine (Pinus taeda L.) reveals a dramatic decline by epicotyl cuttings, which do not root at all in 20–30 days in the presence or absence of auxin. In contrast, almost all the hypocotyls root during this time, but only in the presence of exogenously applied auxin. The failure of epicotyls to root does not appear to be due to differences in [14C]‐labeled auxin uptake, transport, metabolism, or tissue distribution in the two types of cuttings. At the cellular level, initial responses to auxin, such as differentiation of the cambium into parenchyma, occur in both types of cuttings, but localized rapid cell division and root meristem organization are not observed in epicotyls. Autoradiography revealed that radioactivity from a‐naphthalene acetic acid is bound in the cortex but not concentrated at sites of root meristem organization prior to the organization of the meristem in hypocotys. During the development of the epicotyl. cellular competence to form roots appears to be lost. Although this loss in competence is not associated with a concurrent loss in ability to transport auxin polarly, the latter process appears to play a key role in rooting other than to move auxin to the site of root formation. The phytotropin N‐(1‐naphthyl)phthalamic acid inhibits rooting if applied during the first 3 days after the cutting is made, but does not affect auxin concentration or metabolism at the rooting site.

Genetic resistance to disease incited by necrotrophic pathogens is not well understood in plants.Whereas resistance is often quantitative, there is limited information on the genes that underpin quantitative variation in disease resistance. We used a population genomic approach to identify genes in loblolly pine (Pinus taeda) that are associated with resistance to pitch canker, a disease incited by the necrotrophic pathogen Fusarium circinatum. A set of 498 largely unrelated, clonally propagated genotypes were inoculated with F. circinatum microconidia and lesion length, a measure of disease resistance, data were collected 4, 8, and 12 weeks after inoculation. Best linear unbiased prediction was used to adjust for imbalance in number of observations and to identify highly susceptible and highly resistant genotypes (''tails''). The tails were reinoculated to validate the results of the full population screen. Significant associations were detected in 10 single nucleotide polymorphisms (SNPs) (out of 3938 tested). As hypothesized for genes involved in quantitative resistance, the 10 SNPs had small effects and proposed roles in basal resistance, direct defense, and signal transduction. We also discovered associated genes with unknown function, which would have remained undetected in a candidate gene approach constrained by annotation for disease resistance or stress response.

Summary• The metabolome of a plant comprises all small molecule metabolites, which are produced during cellular processes. The genetic basis for metabolites in nonmodel plants is unknown, despite frequently observed correlations between metabolite concentrations and stress responses. A quantitative genetic analysis of metabolites in a nonmodel plant species is thus warranted.• Here, we use standard association genetic methods to correlate 3563 single nucleotide polymorphisms (SNPs) to concentrations of 292 metabolites measured in a single loblolly pine (Pinus taeda) association population.• A total of 28 single locus associations were detected, representing 24 and 20 unique SNPs and metabolites, respectively. Multilocus Bayesian mixed linear models identified 2998 additional associations for a total of 1617 unique SNPs associated to 255 metabolites. These SNPs explained sizeable fractions of metabolite heritabilities when considered jointly (56.6% on average) and had lower minor allele frequencies and magnitudes of population structure as compared with random SNPs.• Modest sets of SNPs (n = 1-23) explained sizeable portions of genetic effects for many metabolites, thus highlighting the importance of multi-SNP models to association mapping, and exhibited patterns of polymorphism consistent with being linked to targets of natural selection. The implications for association mapping in forest trees are discussed.

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To better understand the within-tree variations between juvenile wood, mature wood, and compression wood, wood from a 35-year-old mature bent loblolly pine was separated into seven groups by different positions in the tree. Morphological and chemical structure analyses, including fiber quality, X-ray diffraction, sugar and lignin content analysis, as well as nitrobenzene oxidation, ozonation, and advanced NMR spectroscopy, were performed. Fiber properties were significantly different for tree-top juvenile normal wood and tree-bottom juvenile normal wood, juvenile normal and mature normal wood, juvenile compression and mature compression wood. However, differences in the chemical structure and composition were less significant within the specific tissues indicated above.