The American Chestnut Foundation

The soilborne oomycete Phytophthora cinnamomi-which causes root rot, trunk cankers, and stem lesions on an estimated 5,000 plant species worldwide-is a lethal pathogen of American chestnut (Castanea dentata) as well as many other woody plant species. P. cinnamomi is particularly damaging to chestnut and chinquapin trees (Castanea spp.) in the southern portion of its native range in the United States due to relatively mild climatic conditions that are conductive to disease development. Introduction of resistant genotypes is the most practical solution for disease management in forests because treatment with fungicides and eradication of the pathogen are neither practical nor economically feasible in natural ecosystems. Using backcross families derived from crosses of American chestnuts with two resistant Chinese chestnut cultivars Mahogany and Nanking, we constructed linkage maps and identified quantitative trait loci (QTLs) for resistance to P. cinnamomi that had been introgressed from these Chinese chestnut cultivars. In total, 957 plants representing five cohorts of three hybrid crosses were genotyped by sequencing and phenotyped by standardized inoculation and visual examination over a 6-year period from 2011 to 2016. Eight parental linkage maps comprising 7,715 markers were constructed, and 17 QTLs were identified on four linkage groups (LGs): LG_A, LG_C, LG_E, and LG_K. The most consistent QTLs were detected on LG_E in seedlings from crosses with both 'Mahogany' and 'Nanking' and LG_K in seedlings from 'Mahogany' crosses. Two consistent large and medium effect QTLs located ∼10 cM apart were present in the middle and at the lower end of LG_E; other QTLs were considered to have small effects. These results imply that the genetic architecture of resistance to P. cinnamomi in Chinese chestnut × American chestnut hybrid progeny may resemble the P. sojae-soybean pathosystem, with a few dominant QTLs along with quantitatively inherited partial resistance conferred by multiple small-effect QTLs.

The first genetic map of cranberry (Vaccinium macrocarpon) has been constructed, comprising 14 linkage groups totaling 879.9cM with an estimated coverage of 82.2%. This map, based on four mapping populations segregating for field fruit-rot resistance, contains 136 distinct loci. Mapped markers include blueberry-derived simple sequence repeat (SSR) and cranberry-derived sequence-characterized amplified region markers previously used for fingerprinting cranberry cultivars. In addition, SSR markers were developed near cranberry sequences resembling genes involved in flavonoid biosynthesis or defense against necrotrophic pathogens, or conserved orthologous set (COS) sequences. The cranberry SSRs were developed from next-generation cranberry genomic sequence assemblies; thus, the positions of these SSRs on the genomic map provide information about the genomic location of the sequence scaffold from which they were derived. The use of SSR markers near COS and other functional sequences, plus 33 SSR markers from blueberry, facilitates comparisons of this map with maps of other plant species. Regions of the cranberry map were identified that showed conservation of synteny with Vitis vinifera and Arabidopsis thaliana. Positioned on this map are quantitative trait loci (QTL) for field fruit-rot resistance (FFRR), fruit weight, titratable acidity, and sound fruit yield (SFY). The SFY QTL is adjacent to one of the fruit weight QTL and may reflect pleiotropy. Two of the FFRR QTL are in regions of conserved synteny with grape and span defense gene markers, and the third FFRR QTL spans a flavonoid biosynthetic gene.

An overview of recent achievements and development of genomic resources in the Fagaceae is provided, with major emphasis on the genera Castanea and Quercus. The Fagaceae is a large plant family comprising more than 900 species belonging to 8–10 genera. Using a wide range of molecular markers, population genetics and gene diversity surveys were the focus of many studies during the past 20 years. This work set the stage for investigations in genomics beginning in the early 1990s and facilitated the application of genetic and quantitative trait loci mapping approaches. Transferability of markers across species and comparative mapping have indicated tight macrosynteny between Quercus and Castanea. Omic technologies were more recently developed and the corresponding resources are accessible via electronic and physical repositories (expressed sequence tag sequences, single-nucleotide polymorphisms, candidate genes, cDNA clones, bacterial artificial chromosome (BAC) libraries) that have been installed in North America and Europe. BAC libraries and physical maps were also constructed in Castanea and Quercus and provide the necessary resources for full nuclear genome sequencing projects that are currently under way in Castanea mollissima (Chinese chestnut) and Quercus robur (pedunculate oak).

Protein and oil are the most important components of soybean [Glycine max (L.) Merr.], and they have been shown to have an inverse relationship. As there is a growing demand for soybean oil-based diesel as an alternative fuel source, a better understanding of the protein–oil inverse relationship in conjunction with seed yield could be useful in determining the potential of soybean as a source of biodiesel. We retrospectively examined advanced soybean breeding lines from multiple breeding programs across the southern USA to determine associations between protein and oil and seed yield. The data analyzed were a subset of the Uniform Soybean Tests and consisted of 31 different soybean breeding lines and four checks grown at 10 locations in 2000, six locations in 2001, and eight locations in 2002. A progressive multiple regression analysis was used to develop a single equation describing seed yield over all entries, locations, and years as a function of five traits: oil content, protein content, maturity, lodging, and plant height. From this equation, the optimum plant type for maximum seed yield in the southern USA had either high oil (225 g kg−1) and low protein (385 g kg−1), or high protein (437 g kg−1) and low oil (190 g kg−1). Seed yield continues to be the dominant trait of selection in soybean breeding programs. This study demonstrates that high yield can be achieved with either high protein or high oil. Hence, there is potential for maintaining yield while improving soybean cultivars for oil production. Given the energy balance between fossil-derived and soy-derived diesel, if soy-based biodiesel is to be a significant option, an increased focus on developing high-oil/high-yield soybean needs to occur.

The National Science Foundation of the United States has funded a four-year project to develop genomic tools for the Fagaceae, the beech family, which includes chestnut (Castanea), oak (Quercus), and beech (Fagus). A large amount of cDNA sequence of Castanea, Quercus, and Fagus is being generated by pyrosequencing, a new technique that can produce large amounts of DNA sequence at a lower cost per nucleotide than conventional Sanger-Coulson sequencing. New molecular markers, primarily Single-Nucleotide Polymorphisms, are being discovered, and three Bacterial Artificial Chromosome Libraries of Castanea mollissima cv. 'Vanuxem' have been generated and are available for purchase at the Clemson University Genomics Institute. All sequence information generated by the project will be available on-line at www.fagaceae.org.

Soybean [Glycine max (L.) Merr.] seed produced in high‐temperature, high‐humidity production environments is prone to have substandard germination. Hardseededness, wrinkled seed coats, and infection by Phomopsis longicolla Hobbs are all known to affect soybean seed germinability. Ancestors of modern U.S. soybean cultivars may lack the necessary variability to impart high germinability to new cultivars without the introgression of new genetic diversity. The purpose of this research was to identify soybean germplasm possessing positive traits affecting high seed germinability for seed produced under high‐temperature environments, such as in the early soybean production system (ESPS) of the midsouthern United States. Seed was produced in the ESPS for 486 U.S. plant introductions (PI), 25 ancestral lines of U.S. cultivars, and four U.S. cultivars at Stoneville, MS, in 2002 and 2003. Standard and accelerated‐aging germination percentages, hardseededness, seed coat wrinkling, and incidence of P. longicolla were estimated for each line. Based on the 2002 and 2003 field data, 42 PIs were selected for further testing, along with three cultivars, in two greenhouse temperature regimes (36° and 42°C) at Stoneville, MS, in 2005. Standard field germinations for the 25 ancestral lines ranged from 26 to 82%. Sixty‐three accessions were identified as having a mean standard field germination of ≥90%, <10% hard seed and P. longicolla infection, and ≤10% wrinkled seed coat. Genotypes with excellent seed traits have now been identified for soybean breeders to use in developing improved cultivars with high seed germinability for use in high‐temperature production environments.

Abstract American [Castanea dentata (Marsh) Borkh.] × Chinese [Castanea mollissima Blume] chestnut (Fagac, ae) hybrids are a novel system in which to study influences of phytopathogenic fungi and woody plant hybridization on herbivore susceptibility, as the hybrids are well characterized with regard to resistance to the chestnut blight fungus [Cryphonectria parasita (Murr) Barr (Endothia) Diaporthales: Valsaceae] and variability is present. We chose two groups of resistance‐rated backcross chestnut that shared an F1 parent and had different American parents. Foliage from both backcross groups and the parent trees was sampled on three dates for use in feeding assays with gypsy moth larvae [Lymantria dispar (L.) [Lepidoptera: Lymantriidae], adult Japanese beetles [Popillia japonica Newman (Coleoptera: Scarabaeidae)], and fall webworm larvae [Hyphantria cunea Drury (Lepidoptera: Arctiidae)], respectively. Foliar analyses were performed concurrently and included carbohydrate, tannin, and nitrogen content, toughness, and density. Blight resistance had almost no effect on herbivore performance or foliar chemistry. When the parent trees and backcross groups were compared, however, significant differences in gypsy moth performance and Japanese beetle consumption were evident. There were no differences in fall webworm consumption. Most foliar characteristics measured differed among chestnut genotypes at some point in the season, and all varied seasonally. No clear pattern emerges with respect to the relationship among blight resistance, herbivore susceptibility, foliar properties, and plant genotype, and more research is needed to separate these effects.

"Institutions: The American Chestnut Foundation ." Environment: Science and Policy for Sustainable Development, 34(10), pp. 4–5