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Newman, E.D.; Rowland, J.B.; Hammer, T.G.; Frost, L.A.; Lumibao, C.Y., and Henning, J.A. 2024. Trade-offs in arbuscular mycorrhizal fungal responses to drought and salinity stress in Panicum amarum (United States Gulf Coast). Journal of Coastal Research, 40(1), 51–63. Charlotte (North Carolina), ISSN 0749-0208. Arbuscular mycorrhizal fungi (AMF) are soil and plant root-inhabiting fungi that form symbiotic associations with approximately 95% of terrestrial vascular plants and can aid in survival, growth, and stress tolerance of colonized plants. Coastal dune plants face constant environmental stress from high temperatures, sand burial, low moisture and nutrient retention, and frequent saltwater inundation. Instances of both drought and saltwater inundation stress are predicted to increase as sea levels rise and tropical storm frequency, intensity, and duration increases, with more intense periods of drought between storms. To determine whether native AMF from the United States Gulf Coast improve drought or saltwater inundation tolerance of Panicum amarum, a common Gulf Coast dune grass, a manipulative, crossed-factor greenhouse experiment was conducted by growing P. amarum with and without native AMF under drought or across a gradient of saltwater inundation concentrations: 0.25%, 0.50%, 1.00%, and 1.50%. Under 0.25% salinity, P. amarum grown with native AMF had roughly 47% greater survival, although there were no significant differences in biomass of P. amarum between live and sterile sand treatments. Under drought conditions, plants grown with native AMF had 47% lower survival and three times less biomass than those without native AMF communities. Growth differences between sand treatments were diminished under control conditions, and P. amarum grown with and without native AMF had similar survival and biomass. Despite AMF colonization, P. amarum survival was drastically reduced as salinity concentrations surpassed 0.25%. In conclusion, United States Gulf Coast dune AMF improve salinity inundation tolerance of P. amarum at low salt concentrations; however, the results emphasize the context-dependency of plant responses to AMF colonization. [ABSTRACT FROM AUTHOR]

Tall fescue (Festuca arundinacea Schreb.) is one of the most important cool-season perennial obligatory outcrossing forage grasses in the United States. The production and persistence of tall fescue is significantly affected by drought in the south-central United States. Shoot-specific endophyte (Epichloë coenophiala)-infected tall fescue showed superior performance under both biotic and abiotic stress conditions. We performed a genome-wide association analysis using clonal pairs of novel endophyte AR584-positive (EP) and endophyte-free (EF) tall fescue populations consisting of 205 genotypes to identify marker-trait associations (MTAs) that contribute to drought tolerance. The experiment was performed through November 2014 to June 2018 in the field, and phenotypic data were taken on plant height, plant spread, plant vigor, and dry biomass weight under natural summer conditions of sporadic drought. Genotyping-by-sequencing of the population generated 3,597 high quality single nucleotide polymorphisms (SNPs) for further analysis. We identified 26 putative drought responsive MTAs (17 specific to EP, eight specific to EF, and one in both EP and EF populations) and nine of them (i.e., V.ep_10, S.ef_12, V.ep_27, HSV.ef_31, S.ep_30, SV.ef_32, V.ep_68, V.ef_56, and H.ef_57) were identified within 0.5 Mb region in the tall fescue genome (44.5–44.7, 75.3–75.8, 77.5–77.9 and 143.7–144.2 Mb). Using 26 MTAs, 11 tall fescue genotypes were selected for subsequent study to develop EP and EF drought tolerant tall fescue populations. Ten orthologous genes (six for EP and four for EF population) were identified in Brachypodium genome as potential candidates for drought tolerance in tall fescue, which were also earlier reported for their involvement in abiotic stress tolerance. The MTAs and candidate genes identified in this study will be useful for marker-assisted selection in improving drought tolerance of tall fescue as well opening avenue for further drought study in tall fescue. [ABSTRACT FROM AUTHOR]

Pine-oak forests of the Southwestern United States contain a unique mixture of species that are distributed across light, temperature, and moisture resource gradients. Pines and oaks in this region have developed an array of physiological and structural mechanisms that promote their success in hot, dry environments with high incident solar radiation. This article reviews the structural and physiological mechanisms responsible for the current abundance and distribution patterns of pines and oaks in high elevation woodlands of the Southwest. It highlights the niche differentiation of species as functions of their stress tolerance or avoidance strategies. This review reveals that pinyon pines are generally more stress tolerant than oaks, but that oaks are more tolerant of extreme growing conditions than other pines of the Southwest. While limited information exists that describes the physiological ecology of some of the pines and oaks in this biogeographical region, there are many opportunities for future research that could contribute to a more holistic understanding of species-environment relationships in Southwestern forests. [ABSTRACT FROM AUTHOR]

Average commercial maize yield in the US has increased from about 1 Mg/ha in the 1930s to about 7 Mg/ha in the 1990s. Although the increase has been the result of both genetic and agronomic-management improvements, we contend that most of this improvement is the result of the genotype×management interaction. The genetic improvement in maize yield is associated neither with yield potential per se, nor with heterosis per se, but it is associated with increased stress tolerance, which is consistent with the improvement in the genotype×management interaction. The potential for future yield improvement through increased stress tolerance of maize in the US is large, as yield potential is approximately three times greater than current commercial maize yields. The mechanism by which maize breeders have improved stress tolerance is not known, but we speculate that increased stress tolerance may have resulted from the selection for yield stability. Stability analyses were performed on a number of high-yielding maize hybrids, including three hybrids that have been involved in some of the highest maize yields recorded in producers’ fields, to examine the relationship between yield and yield stability. Results of the stability analyses showed that high-yielding maize hybrids can differ in yield stability, but results do not support the contention that yield stability and high grain yield are mutually exclusive. [Copyright &y& Elsevier]

Salmonella enterica serovar Heidelberg is currently the 12th most common serovar of Salmonella enterica causing salmonellosis in the United States and results in twice the average incidence of blood infections caused by nontyphoidal salmonellae. Multiple outbreaks of salmonellosis caused by Salmonella Heidelberg resulted from the same poultry processor, which infected 634 people during 2013 and 2014. The hospitalization and invasive illness rates were 38% and 15%, respectively. We hypothesized that the outbreak strains of Salmonella Heidelberg had enhanced stress tolerance and virulence capabilities. We sourced nine food isolates collected during the outbreak investigation and three reference isolates to assess their tolerance to heat and sanitizers, ability to attach to abiotic surfaces, and invasiveness in vitro We performed RNA sequencing on three isolates (two outbreak-associated isolates and a reference Salmonella Heidelberg strain) with various levels of heat tolerance to gain insight into the mechanism behind the isolates' enhanced heat tolerance. We also performed genomic analyses to determine the genetic relationships among the outbreak isolates. Ultimately, we determined that (i) six Salmonella Heidelberg isolates associated with the foodborne outbreak had enhanced heat tolerance, (ii) one outbreak isolate with enhanced heat tolerance also had an enhanced biofilm-forming ability under stressful conditions, (iii) exposure to heat stress increased the expression of Salmonella Heidelberg multidrug efflux and virulence genes, and (iv) outbreak-associated isolates were likely transcriptionally primed to better survive processing stresses and, potentially, to cause illness. IMPORTANCE This study provides a deep analysis of the intrinsic stress tolerance and virulence capabilities of Salmonella Heidelberg that may have contributed to the length and severity of a recent salmonellosis outbreak. Additionally, this study provides a comprehensive analysis of the transcriptomic response of S. enterica strains to heat stress conditions and compares baseline stationary-phase gene expression among outbreak- and non-outbreak-associated Salmonella Heidelberg isolates. These data can be used in assay development to screen isolates for stress tolerance and subsequent survival. This study adds to our understanding of the strains associated with the outbreak and informs ongoing regulatory discussions on Salmonella in poultry., (Copyright © 2019 American Society for Microbiology.)