Is it feasible to improve stand persistence of eastern gamagrass (Tripsacum dactyloides L.) through breeding?

Abstract Eastern gamagrass is a warm‐season perennial grass that has excellent forage nutritional quality and a broad range of adaptations. Despite the favorable forage qualities, agronomic issues persist; most important for grazing systems is stand persistence from preferential grazing when growing in mixed species communities. Stand persistence when monoculture stands are grazed has been previously studied, and it has been observed that stands decline under high stocking rates or low grazing height. The objective of our study was to evaluate if an improvement of stand persistence under defoliation to a low‐cut height is feasible through the breeding of improved lines. A persistence trial was conducted using a completely random design and eight replications to evaluate the stand persistence of two commercial cultivars, two experimental lines, and an ecotype selection. Defoliation occurred by grazing and mowing to a height of 8 cm three‐to‐four times over the course of five growing seasons. Stand counts of live plants were taken following the final defoliation of the season. Mixed linear regression modeling indicates significant differences between genotypes developed in years where no grazing occurred. An ecotype selection from Northwest Oklahoma exhibited significantly greater persistence than the cultivar Pete and the other experimental lines. These results suggest that different alleles exist for critical persistence genes, indicating it may be feasible to improve the trait through breeding and selection

Estimating reliability for evaluating nitrate accumulation in sorghum (Sorghum bicolor L. Moench) inbred A‐lines

Abstract Sorghum is an important forage crop in many cropping systems. Nitrate can accumulate in the vegetative plant tissue to levels high enough that result in fatality when fed to ruminant livestock when grown under high nitrate conditions. If variation among inbred lines can be documented for nitrate concentration, it may be possible to reduce nitrate accumulation within forage sorghum hybrids by selecting inbred lines having lower nitrate accumulation. The goal of this study was to evaluate a diverse set of male‐sterile sorghum inbred lines grown under high nitrate conditions, to observe if genotypic variation exists among lines used to produce forage sorghum hybrids. Forty replicates of 20 sorghum A‐lines were grown in a greenhouse and received either 272 kg ha−1 or 408 kg ha−1 of actual nitrogen per plant through applications of ammonium nitrate. Variance components were extracted from linear regression models and reliability was estimated on an entry‐mean basis. Leaf and stem reliability estimates were 0.95 and 0.93, respectively. These reliability estimates indicate the genetic variance comprised most of the phenotypic variance, and that our measurements were consistent. Significant differences were also observed between genotypes for both leaf and stem tissue. Therefore, sufficient genetic variance exists for developing male sterile sorghum inbred lines having leaf nitrate concentrations below the potentially lethal toxicity threshold of 10,000 μg g−1

Variation in degree of pollen exclusion for ga1-s unilateral cross incompatibility in temperate maize breeding populations

Fertilization and kernel development are crucial for breeding and agronomic production of maize (Zea mays L.), which is prone to outcrossing. Because of this tendency, a major issue for organic corn farmers is to maintain genetic purity of their crop. One way to maintain this purity is to use a unilateral cross incompatibility system such as Ga1-s. However, lack of complete pollen exclusion has been reported in Ga1-s heterozygotes, complicating introgression of this trait into breeding germplasm. A systematic, quantitative evaluation of pollen exclusion rates in breeding lines would greatly facilitate use of this system. The purpose of this study is to quantitatively evaluate exogenous ga1 pollen exclusion of a diverse set of Ga1-s/ga1 F1 hybrids representing the stiff stalk and nonstiff stalk heterotic groups, and the Iowa Synthetic Corn Borer population. Differences between genotypes but not heterotic groups were observed when applying exogenous ga1 pollen onto heterozygotes possessing the same Ga1-s allele, indicating there are epistatic interactions between Ga1-s and modifier loci in the ga1 parents tested.This article is published as Boerman, Nicholas A., Adrienne N. Moran Lauter, Jode W. Edwards, and M. Paul Scott. "Variation in degree of pollen exclusion for ga1‐s unilateral cross incompatibility in temperate maize breeding populations." Agrosystems, Geosciences & Environment 4, no. 4 (2021): e20220. doi:10.1002/agg2.20220.Works produced by employees of the U.S. Government as part of their official duties are not copyrighted within the U.S. The content of this document is not copyrighted

The Ga1 locus of the genus Zea is associated with novel genome structures derived from multiple, independent nonhomologous recombination events

The Ga1 locus controls cross-incompatibility between field corn and popcorn. The Ga1-S haplotype contains 2 types of pectin methylesterase (PME) genes, ZmPme3 and several copies of ZmGa1P that are expressed in silk and pollen, respectively. The ga1 haplotype contains nonfunctional tandem repeat sequences related to ZmPme3 and ZmGa1P. This haplotype can cross-pollinate freely and is widely present in field corn. The primary objective of this study is to characterize the repeat sequences from a diverse collection of maize and teosinte lines and use this information to understand the evolution of the Ga1 locus. First, we characterized the complexity of the Ga1 genome region in high-quality maize genome assemblies that led to their categorization into 5 groups based on the number and type of PME-like sequences found at this region. Second, we studied duplication events that led to the ga1 and Ga1-S repeats using maximum likelihood phylogenetic reconstruction. Divergence estimates of the ga1 haplotype suggest that the duplication events occurred more than 600 KYA whereas those in Ga1-S occurred at 3 time points, i.e. >600, ∼260, and ∼100 KYA. These estimates suggest that the ga1 and Ga1-S tandem duplication events occurred independently. Finally, analysis of ZmPme3 and ZmGa1P homologs in Zea and Tripsacum genomes suggests that ga1 and Ga1-S repeats originated from an ancestral pair of PME genes that duplicated and diverged through 2 evolutionary branches prior to the domestication of maize.This article is published as Amruta R Bapat, Adrienne N Moran Lauter, Matthew B Hufford, Nicholas A Boerman, M Paul Scott, The Ga1 locus of the genus Zea is associated with novel genome structures derived from multiple, independent nonhomologous recombination events, G3 Genes|Genomes|Genetics, Volume 13, Issue 11, November 2023, jkad196, https://doi.org/10.1093/g3journal/jkad196.This work is written by (a) US Government employee(s) and is in the public domain in the US