Loci Controlling Resistance to High Plains Virus and Wheat Streak Mosaic Virus in a B73 × Mo17 Population of Maize

High Plains disease has the potential to cause significant yield loss in susceptible corn (Zea mays L.) and wheat (Triticum aestivum L.) genotypes, especially in the central and western USA. The primary causal agent, High Plains virus (HPV), is vectored by wheat curl mite (WCM; Aceria tossicheila Keifer), which is also the vector of wheat streak mosaic virus (WSMV). In general, the two diseases occur together as a mixed infection in the field. The objective of this research was to characterize the inheritance of HPV and WSMV resistance using B73 (resistant to HPV and WSMV) × Mo17 (moderately susceptible to HPV and WSMV) recombinant inbred lines. A population of 129 recombinant inbred lines scored for 167 molecular markers was used to evaluate resistance to WSMV and to a mixed infection of WSMV and HPV. Loci conferring resistance to systemic movement of WSMV in plants mapped to chromosomes 3, 6, and 10, consistent with the map position of wsm2, wsm1, and wsm3, respectively. Major genes for resistance to systemic spread of HPV in doubly infected plants mapped to chromosomes 3 and 6, coincident or tightly linked with the WSMV resistance loci. Analysis of doubly infected plants revealed that chromosome 6 had a major effect on HPV resistance, consistent with our previous analysis of B73 × W64A and B73 × Wf9 populations. Quantitative trait loci (QTL) affecting resistance to localized symptom development mapped to chromosomes 4 (umc66), 5 (bnl5.40), and 6 (umc85), and accounted for 24% of the phenotypic variation. Localized symptoms may reflect the amount of mite feeding or the extent of virus spread at the point of infection. Identification of cosegregating markers may facilitate selection for HPV and WSMV resistance in corn breeding programs

Evaluation of 41 elite and exotic inbred\u3ci\u3e Sorghum\u3c/i\u3e genotypes for high quality callus production

Interest is high in the genetic study and improvement of sorghum(Sorghum bicolor L. Moench), a crop of worldwide agronomic importance. The ability to initiate and maintain high quality (pigmentless, mucilage-free, fast growing, type II) callus cultures from a variety of sorghum genotypes is important for certain tissue culture-based genetic studies. The objective of this study was to identify high-quality callus-producing genotypes from a group of 41 diverse inbred sorghum lines. Callus cultures of 20 elite inbred sorghum genotypes and 21 inbred genotypes of exotic background were initiated from immature inflorescences. The cultures were subjected to several cycles of subculturing with selection for high quality callus growth, then rated for the callus quality traits pigment/tannin production, mucilage production, embryogenesis, and friability. Genotypic effects on each of the traits was highly significant. The range in quality of callus produced by different sorghum genotypes was large. Based on mean ratings assigned for each of the traits, 7 elite inbred genotypes and 5 nonelite genotypes were identified as producers of high quality callus

Media Effects On Phenotype Of Callus Cultures Initiated From Photoperiod-Insensitive, Elite Inbred Sorghum Lines

Sorghum (Sorghum bicolor L. Moench) is a crop of worldwide agronomic importance. Routine production of high quality (friable, embryogenic, fast growing) callus cultures is fundamental to tissue culture based genetic study and improvement of sorghum. Genotype by culture medium interactions for sorghum callus growth and morphology have been previously reported. The objective of this study was to identify tissue culture media that would support high quality callus growth across photoperiod insensitive, relatively elite genotypes. Explants from immature inflorescences of 11 sorghum genotypes were cultured on 6 tissue culture media of differing composition. After 3 and 5 months in culture, calli were rated for pigment and mucilage production, friability, and embryogenesis. Media and genotype effects on callus phenotype were highly significant. Most genotypes produced highest quality callus on MS-based media. Significant genotype by media interactions for callus friability were also documented. Two media formulations, SIM2B5 and N6 were identified as superior for the culture of high quality callus initiated from photoperiod insensitive, elite sorghum lines

Media Effects On Phenotype Of Callus Cultures Initiated From Photoperiod-Insensitive, Elite Inbred Sorghum Lines

Sorghum (Sorghum bicolor L. Moench) is a crop of worldwide agronomic importance. Routine production of high quality (friable, embryogenic, fast growing) callus cultures is fundamental to tissue culture based genetic study and improvement of sorghum. Genotype by culture medium interactions for sorghum callus growth and morphology have been previously reported. The objective of this study was to identify tissue culture media that would support high quality callus growth across photoperiod insensitive, relatively elite genotypes. Explants from immature inflorescences of 11 sorghum genotypes were cultured on 6 tissue culture media of differing composition. After 3 and 5 months in culture, calli were rated for pigment and mucilage production, friability, and embryogenesis. Media and genotype effects on callus phenotype were highly significant. Most genotypes produced highest quality callus on MS-based media. Significant genotype by media interactions for callus friability were also documented. Two media formulations, SIM2B5 and N6 were identified as superior for the culture of high quality callus initiated from photoperiod insensitive, elite sorghum lines

TCUP: A Novel hAT Transposon Active in Maize Tissue Culture

Transposable elements (TEs) are capable of inducing heritable de novo genetic variation. The sequences capable of reactivation, and environmental factors that induce mobilization, remain poorly defined even in well-studied genomes such as maize. We treated maize tissue culture with the demethylating agent 5-aza-2-deoxcytidine and examined long-term tissue culture lines to discover silenced TEs that have the potential to induce heritable genetic variation. Through these screens we have identified a novel low copy number hAT transposon, Tissue Culture Up-Regulated (TCUP), which is transcribed at high levels in long-term maize black Mexican sweet (BMS) tissue culture and is transcribed in response to treatment with 5-aza-2-deoxycytidine. Analysis of the TIGR Maize Gene Index revealed that this element is the most frequently represented EST from the BMS cell culture library and is not represented in other tissue libraries, which is the basis for its name. A full-length sequence was assembled in inbred B73 that contains the putative functional motifs required for autonomous movement of a hAT transposon. Transposon display detected novel TCUP insertions in two long-term tissue-cultured cell lines of the genotype Hi-II A × B and BMS. This research implicates TCUP as a transposon that is capable of reactivation and which may also be particularly sensitive to the stress of the tissue culture environment. Our findings are consistent with the hypothesis that epigenetic alterations potentiate genomic responses to stress during clonal propagation of plants

Selection Signatures in Four Lignin Genes from Switchgrass Populations Divergently Selected for \u3ci\u3eIn Vitro\u3c/i\u3e Dry Matter Digestibility

Switchgrass is undergoing development as a dedicated cellulosic bioenergy crop. Fermentation of lignocellulosic biomass to ethanol in a bioenergy system or to volatile fatty acids in a livestock production system is strongly and negatively influenced by lignification of cell walls. This study detects specific loci that exhibit selection signatures across switchgrass breeding populations that differ in in vitro dry matter digestibility (IVDMD), ethanol yield, and lignin concentration. Allele frequency changes in candidate genes were used to detect loci under selection. Out of the 183 polymorphisms identified in the four candidate genes, twenty-five loci in the intron regions and four loci in coding regions were found to display a selection signature. All loci in the coding regions are synonymous substitutions. Selection in both directions were observed on polymorphisms that appeared to be under selection. Genetic diversity and linkage disequilibrium within the candidate genes were low. The recurrent divergent selection caused excessive moderate allele frequencies in the cycle 3 reduced lignin population as compared to the base population. This study provides valuable insight on genetic changes occurring in short-term selection in the polyploid populations, and discovered potential markers for breeding switchgrass with improved biomass quality

On the Use of High-Frequency Surface Wave Oceanographic Research Radars as Bistatic Single-Frequency Oblique Ionospheric Sounders

We demonstrate that bistatic reception of high-frequency oceanographic radars can be used as single-frequency oblique ionospheric sounders. We develop methods that are agnostic of the software-defined radio system to estimate the group range from the bistatic observations. The group range observations are used to estimate the virtual height and equivalent vertical frequency at the midpoint of the oblique propagation path. Uncertainty estimates of the virtual height and equivalent vertical frequency are presented. We apply this analysis to observations collected from two experiments run at two locations in different years, but utilizing similar software-defined radio data collection systems. In the first experiment, 10 d of data were collected in March 2016 at a site located in Maryland, USA, while the second experiment collected 20 d of data in October 2020 at a site located in South Carolina, USA. In both experiments, three Coastal Oceanographic Dynamics and Applications Radars (CODARs) located along the Virginia and North Carolina coast of the US were bistatically observed at 4.53718 MHz. The virtual height and equivalent virtual frequency were estimated in both experiments and compared with contemporaneous observations from a vertical incident digisonde-ionosonde at Wallops Island, VA, USA. We find good agreement between the oblique CODAR-derived and WP937 digisonde virtual heights. Variations in the virtual height from the CODAR observations and the digisonde are found to be nearly in phase with each other. We conclude from this investigation that observations of oceanographic radar can be used as single-frequency oblique incidence sounders. We discuss applications with respect to investigations of traveling ionospheric disturbances, studies of day-to-day ionospheric variability, and using these observations in data assimilation