Piptochaetium (Poaceae, Pooideae, Stipeae) is a New World genus of grasses distributed primarily in temperate South America, with several species extending into Central and southern North America. The genus comprises 36 species and 2 varieties. Morphological synapomorphies for the genus include involute lemma margins that fit into the palea groove, a bi‐keeled palea longer than the lemma and protruding from the lemma apex, and fundamental cell sidewalls that are regularly dentate. The closely related genera Nassella (116 species) and Jarava (59 species) are also primarily South American, with a few species found in Central and North America. Published molecular studies to date have focused upon generic‐level relationships within the tribe Stipeae, but none have included more than a few representatives of each genus. We present here results of phylogenetic analyses of these genera based upon combined DNA sequences of both nuclear (ITS) and cpDNA (rpl16, trnL‐F) markers. Piptochaetium is supported as monophyletic in all studies, whereas Nassella is recovered as monophyletic only if Jarava plumosa is included. Infrageneric relationships of Piptochaetium are also compared to a recent morphological phylogeny of the genus.

Water and nutrient acquisition is a critical function of plant root systems. Root system architecture (RSA) traits are often complex and controlled by many genes. This is the first genome-wide association study reporting genetic loci for RSA traits for field-grown soybean (Glycine max). A collection of 289 soybean genotypes was grown in three environments, root crowns were excavated, and 12 RSA traits assessed. The first two components of a principal component analysis of these 12 traits were used as additional aggregate traits for a total of 14 traits. Marker–trait association for RSA traits were identified using 31,807 single-nucleotide polymorphisms (SNPs) by a genome-wide association analysis. In total, 283 (non-unique) SNPs were significantly associated with one or more of the 14 root traits. Of these, 246 were unique SNPs and 215 SNPs were associated with a single root trait, while 26, four, and one SNPs were associated with two, three, and four root traits, respectively. The 246 SNPs marked 67 loci associated with at least one of the 14 root traits. Seventeen loci on 13 chromosomes were identified by SNPs associated with more than one root trait. Several genes with annotation related to processes that could affect root architecture were identified near these 67 loci. Additional follow-up studies will be needed to confirm the markers and candidate genes identified for RSA traits and to examine the importance of the different root characteristics for soybean productivity under a range of soil and environmental conditions.

mays L. is one of the world’s most important and widely grown crops and is susceptible to a wide range of plant pathogens. One fungal pathogen of particular concern is Aspergillus flavus Link, which is capable of producing the secondary metabolite aflatoxin. Aflatoxin poses serious health concerns when consumed by humans and animals and when consumed in large doses can lead to abdominal pain, liver damage, and death. While regulated in the United States, many underdeveloped countries do not have the resources to monitor aflatoxin accumulation in maize and, thus, developing low aflatoxin accumulation commercial maize lines would be of great benefit. The objective of this project was to identify genotypic and phenotypic predictors of low aflatoxin accumulation that could help maize breeders develop a low aflatoxin accumulating line. First, the inheritance pattern of low aflatoxin accumulation was investigated in a series of reciprocal crosses between a high toxin accumulating line and a low toxin accumulating line. The data supported the hypothesis that maternal effects or the interaction between nuclear and maternal genetic components impacts aflatoxin accumulation. Second, the availability of sugars in maize kernels has been shown in laboratory studies to impact aflatoxin production and accumulation in A. flavus grown on media. To determine if sugars impact maize grown in the field, aflatoxin accumulation was analyzed in maize starch biosynthesis mutants and four mutants were identified that accumulate significantly high aflatoxin concentrations. These maize mutants have unique phenotypic characteristics such as high sugar concentrations, altered starch ratios and high moisture that could aid A. flavus in aflatoxin production. The impact of sugar on aflatoxin accumulation was also evaluated in a diverse set of maize germplasm providing further evidence for the relationship between sugar availability and aflatoxin accumulation. Finally, two QTL chromosome regions were identified in maize cob tissue, a maternally derived tissue. Candidate genes in these regions associated with low aflatoxin accumulation include genes for the transport of sugars and disease resistance. The results of this work reveal the potential impact the maternal parental plant has on low aflatoxin accumulation through the movement of carbohydrates into developing kernels, how maternal tissues (e.g. husks, cob and pericarp) serve as barriers to fungal infection and the location of QTL in the maize genome associated with low aflatoxin accumulation.