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Torreya taxifolia Arn. (Florida torreya) is a critically endangered (International Union for Conservation of Nature 3.1) conifer with a very limited native range in the USA, occurring in two counties in Florida and one in Georgia where it persists in ravines along the Apalachicola River. The species suffered a major decline, ∼ 99% loss, beginning in the 1930s, with a total population estimated at 357,500 in the early 1900s decreasing to 1,000 individuals currently remaining in the wild. The initial decline was attributed to an unknown fungal disease with Fusarium torreyae (T. Aoki, J. A. Smith, L. Mount, Geiser and O'Donnell), identified in 2011 as the causal agent of a canker disease. The objectives of this work were to develop genetic markers to uniquely identify individuals, examine the structure of the in situ population, and use an ex situ germplasm resource to determine if reproduction without fertilization (apomixis) occurs. We developed a panel of microsatellite markers, sampled individuals from three natural in situ populations, and found population structure at all levels tested. The markers were next applied to ex situ mothers, potential fathers, and progeny to investigate the occurrence of apomixis. One of 29 progeny seedlings tested and its mother had identical multilocus genotypes. The probability of observing this genotype by chance, given the mother and the two possible fathers' genotypes, is approximately one in ten. Based on these data, we cannot reject the hypothesis that apomixis occurs. Our finding of population structure suggests genotypes from as wide an area as possible are required to capture the diversity of the species in conservation efforts. The multiplexed marker panel can be used to identify individual accessions and assist with managing ex situ collections; however, they are not informative enough to clearly differentiate closely related individuals in the ex situ population. [ABSTRACT FROM AUTHOR]

Chestnut blight (caused by Cryphonectria parasitica), together with Phytophthora root rot (caused by Phytophthora cinnamomi), has nearly extirpated American chestnut (Castanea dentata) from its native range. In contrast to the susceptibility of American chestnut, many Chinese chestnut (C. mollissima) genotypes are resistant to blight. In this research, we performed a series of genome-wide association studies for blight resistance originating from three unrelated Chinese chestnut trees (Mahogany, Nanking and M16) and a Quantitative Trait Locus (QTL) study on a Mahogany-derived inter-species F2 family. We evaluated trees for resistance to blight after artificial inoculation with two fungal strains and scored nine morpho-phenological traits that are the hallmarks of species differentiation between American and Chinese chestnuts. Results support a moderately complex genetic architecture for blight resistance, as 31 QTLs were found on 12 chromosomes across all studies. Additionally, although most morpho-phenological trait QTLs overlap or are adjacent to blight resistance QTLs, they tend to aggregate in a few genomic regions. Finally, comparison between QTL intervals for blight resistance and those previously published for Phytophthora root rot resistance, revealed five common disease resistance regions on chromosomes 1, 5, and 11. Our results suggest that it will be difficult, but still possible to eliminate Chinese chestnut alleles for the morphophenological traits while achieving relatively high blight resistance in a backcross hybrid tree. We see potential for a breeding scheme that utilizes marker-assisted selection early for relatively large effect QTLs followed by genome selection in later generations for smaller effect genomic regions. [ABSTRACT FROM AUTHOR]

Abstract: The objective of this study is to analyze patterns of genetic variation at genic expressed sequence tag--simple sequence repeats (EST-SSRs) andat chloroplast DNA markers inpopulations of American chestnut (Castanea [...]

Despite the economic and ecologic importance of pine oleoresins, their rheology remains little explored. In this report we describe rheological properties of oleoresins produced by mature trees of four southern pines native to North America (loblolly, slash, longleaf, shortleaf). Results indicate that these oleoresins are structured fluids that exhibit viscoelastic behavior, but differ in flow behavior. Slash pine oleoresin exhibited Newtonian flow behavior while the oleoresin from the longleaf and shortleaf pines showed pseudoplastic behavior and the loblolly pine oleoresin showed Bingham fluid behavior with a yield stress of about 1.980 Pa. Temperature-dependent viscosities for the oleoresin samples studied were well described by the Arrhenius model, yielding flow activation energies ranging from 153.5 to 219.7 kJ/mol. The viscosity of the slash pine oleoresin sample was found to be less sensitive to temperature than that of the shortleaf or longleaf pine samples. The time-temperature superposition principle was successfully applied to pine oleoresins to show behavior over the temperature range of 25 - 65 °C typical for a thermorheologically simple system. Such behavior is consistent with the temperature dependent viscoelastic properties found for these complex fluids, and supports the effective use of rheological evaluations for describing physical properties of pine oleoresins.

Oak decline is a general term used for the progressive dieback and eventual mortality of oak trees due to many compounding stressors, typically a combination of predisposing, inciting, and contributing factors. While pinpointing individual causes of decline in oak trees is a challenge, past studies have identified site and stand characteristics associated with oak decline. In this study, we developed a risk map of oak decline for the Daniel Boone National Forest (DBNF), combining GIS, remote sensing (RS), and public reporting (citizen science, CS). Starting with ground reports of decline (CS), we developed a site-scale model (GIS and RS) for oak decline based on four previously identified predisposing factors: elevation, slope, solar radiation, and topographic wetness. We found that areas identified in the model as having a high oak decline risk also reflected areas of observed oak decline (CS). We then optimized and expanded this risk model to the entire range of the DBNF, based on both site characteristics (as piloted for the case study site) and stand inventory data. The stand inventory data (including species composition and age) further improved the model, resulting in a risk map at the landscape level. This case study can serve as a planning tool and highlights the potential usefulness of integrating GIS, remote sensing, and citizen science. [ABSTRACT FROM AUTHOR]

Plant breeders contributed enormously to the agricultural and economic development of the United States. By improving the profitability of farming, plant breeders improved the economic condition of farmers and contributed to the growth and structure of rural communities. In the years since World War II, agriculture and the quality of rural life have been driven by policies that encouraged and subsidized an agroindustrial production model. Plant breeders responded by developing methods and deploying products attuned to agroindustrial clients. Major achievements by plant breeders of the era include the development of higher-yielding crops suitable to new environments and mechanized harvesting and shipping. As social, technological, and economic changes reinforced the expansion and dominance of the agroindustrial model, rural communities sustained high levels of out-migration. At the same time, a variety of societal and economic forces have encouraged new food system models, including the locavores and community-supported agriculture. Sustainability indices reflect the desire of megaretailers to make the relationship between consumers and the production of their food more transparent. These forces, along with an increased focus on the quality of rural life in America, represent opportunities for plant breeders to address the needs of new clients, to develop methods appropriate to their client's values, and to serve traditional clients in new ways. doi: 10.2135/cropsci2009.10.0572

We evaluated the precision of phenotypic classification for fusiform rust resistance of Pinus taeda L. in a clonally propagated population segregating for the pathotype-specific resistance gene Fr1. In all marker-defined Fr1/fr1 clones screened with low complexity or ambient inoculum, marker--trait cosegregation was complete with no exceptions. Uncommon exceptions (4 of 30) in which marker-defined Fr1/fr1 clones screened with high complexity inoculum were diseased were probably due to a low frequency of spores virulent to Fr1 resistance. Marker--trait cosegregation for fr1/fr1 clones was less reliable, as all ramets of a few clones (5 of 29, 3 of 25, and 4 of 16) remained disease-free with low complexity, high complexity, or ambient inoculum, respectively. We termed disease-free fr1/fr1 ramets 'escapes', since the genetics of the host--pathogen interaction predicted them to be diseased. For nonmarker-defined materials, we considered escapes to be disease-free ramets within clones that had at least one diseased ramet. Narrow-sense heritability estimates for escape rate were 29% and 23% for the low and high complexity inocula, respectively, suggesting that genetic variation in the host is an important component of this resistance mechanism. Resume: Nous avons evalue la precision d'une classification phenotypique de la resistance du Pinus taeda L. a la rouille fusiforme chez une population propagee de facon clonale et chez qui segregeait le gene de resistance pathotype-specifique Fr1. Chez tous les clones Fr1/fr1 caracterises a l'aide de marqueurs moleculaires et soumis a un inoculum ambiant ou de faible complexite, on a observe une cosegregation marqueur--trait complete, sans exception. Les exceptions peu frequentes (4 sur 30) ou des clones Fr1/fr1 soumis a un inoculum de complexite elevee etaient atteints par la maladie sont possiblement dues a la presence, en faible quantite, de spores virulentes a l'endroit du materiel Fr1. Chez les clones fr1/fr1, la cosegregation marqueur--trait s'est averee moins robuste puisque tous les ramets de quelques clones (respectivement 5 sur 29, 3 sur 25, et 4 sur 16) sont demeures exempts de maladie quelque soit l'inoculum utilise (faible complexite, forte complexite, ou ambiant). Nous avons considere que les ramets fr1/fr1 exempts de maladie ont echappe a la maladie puisqu'on s'attendait a ce qu'ils soient malades selon le modele genetique des interactions hote--pathogene. Dans le cas du materiel vegetal n'ayant pas fait l'objet d'une caracterisation moleculaire, nous avons considere que les ramets exempts de maladie provenant de clones qui comptaient au moins un ramet malade ont echappe a la maladie. Nous avons estime l'heritabilite au sens strict des taux d'echappement a la maladie a 29 % et 23 % respectivement en presence d'inoculum de complexite faible ou elevee, ce qui indique que la variation genetique chez l'hote est une composante importante de ce mecanisme de resistance. [Traduit par la Redaction], Introduction The most important disease of loblolly pine (Pinus taeda L.) and slash pine (Pinus elliottii Engelm. var. elliottii) is fusiform rust, which is incited by a fungal pathogen endemic [...]

Abstract: The island-like populations of Fraser fir (Abies fraseri (Pursh) Poir.) have been isolated since the end of the late-Wisconsinien glaciation on the highest peaks of the Southern Appalachian Mountains [...]

Abstract: A reference karyotype is presented for loblolly pine (Pinus taeda L., subgenus Pinus, section Pinus, subsection Australes), based on fluorescent in situ hybridization (FISH), using 18S-28S rDNA, 5S rDNA, [...]

Genetic association is a powerful method for dissecting complex adaptive traits due to (i) fine-scale mapping resulting from historical recombination, (ii) wide coverage of phenotypic and genotypic variation within a single experiment, and (iii) the simultaneous discovery of loci and alleles. In this article, genetic association among single nucleotide polymorphisms (58 SNPs) from 20 wood- and drought-related candidate genes and an array of wood property traits with evolutionary and commercial importance, namely, earlywood and latewood specific gravity, percentage of latewood, earlywood microfibril angle, and wood chemistry (lignin and cellulose content), was tested using mixed linear models (MLMs) that account for relatedness among individuals by using a pairwise kinship matrix. Population structure, a common systematic bias in association studies, was assessed using 22 nuclear microsatellites. Different phenotype: genotype associations were found, some of them confirming previous evidence from collocation of QTL and genes in linkage maps (for example, 4cl and percentage of latewood) and two that involve nonsynonymous polymorphisms (cad SNP M28 with earlywood specific gravity and 4cl SNP M7 with percentage of latewood). The strongest genetic association found in this study was between allelic variation in [alpha]-tubulin, a gene involved in the formation of cortical microtubules, and earlywood microfibril angle. Intragenic LD decays rapidly in conifers; thus SNPs showing genetic association are likely to be located in close proximity to the causative polymorphisms. This first multigene association genetic study in forest trees has shown the feasibility of candidate gene strategies for dissecting complex adaptive traits, provided that genes belonging to key pathways and appropriate statistical tools are used. This approach is of particular utility in species such as conifers, where genomewide strategies are limited by their large genomes.