Seed dormancy complicates the agricultural use of many legume species. Understanding the genetic and environmental drivers of seed dormancy is necessary for advancing crop improvement for legumes, such as Vicia villosa. In this study, we quantify the magnitude of genetic and environmental effects on physical dormancy among 1488 maternal V. villosa plants from 18 diverse environments. Furthermore, we explore the relationship between physical dormancy and environmental conditions during seed development. Additive genetic variance (h2) accounted for 40% of the variance, while the growing environment explained 28% of the variance in physical dormancy. Maternal lines showed complete variance in physical dormancy, as one line was 100% dormant, and 56 lines were 0% dormant. Distributions of physical dormancy varied widely among seed production environments, with some site-years strongly skewed toward physically dormant seed, while other site-years exhibited little dormant seed. Twenty-three weather variables were associated with environmental and error effects of physical dormancy. High mean and minimum relative humidity, low mean and maximum temperature, and high precipitation weakly grouped with low physical dormancy. Weather variables calculated from fixed time windows approximating seed maturity to seed harvest at each site-year tended to be less predictive than biological seed drying windows calculated based on seed maturity of each maternal line. Overall, individual and cumulative effects of weather variables were poor predictors of physical dormancy. Moderate heritability indicates that breeding programs can select against physical dormancy and improve V. villosa for agricultural use. Marker-based approaches would maximize selection for physical dormancy by reducing the influence of unpredictable environmental effects.
Hairy vetch (Vicia villosa Roth) is a commonly grown legume cover crop in the United States. Critical breeding goals for the species include increasing early fall vigor and spring biomass production. To ascertain genetic improvement for these traits, we explored the relationship between fall and spring vigor. Moreover, we evaluated the variation in genotypic performance across multiple environments and assessed how weather variables affected germplasm performance. The relationship between fall and spring vigor differed by winter weather conditions. In warmer locations, top‐performing genotypes in the fall were the top performers in the spring, allowing simultaneous selection for both traits of interest. Environments with colder winter conditions, however, did not show linear relationships between fall and spring vigor. At cold sites, the most and least vigorous plants in the fall tended to underperform in the spring. Results suggest that fall vigor is not a linear predictor of spring vigor in cold environments, and consequently, breeding programs should screen and select for both traits in cold climates. Genotype × environment interaction (GE) heavily contributed to spring vigor performance. In our dataset, days below freezing without snow cover, days below freezing, minimum daily temperature, and freezing degree days were related to the signal in GE. As a result, breeding programs would benefit from dividing selection sites according to the severity of winter conditions.
Hairy vetch (Vicia villosa Roth) is a winter‐annual legume that is grown as a cover crop and for forage. Although more winter tolerant than most leguminous winter annuals, it does not reliably overwinter in the upper Midwestern United States. Our objectives were to screen a collection of accessions for winter hardiness and develop a screening method for freezing tolerance in a controlled setting. We evaluated 30 accessions (commercial germplasm and breeding populations) in multiple Minnesota environments. Average winter survival among accessions ranged from 13 to 73% and resembled a bimodal distribution, where two distinct phenotypic groupings were apparent. Commercial VNS (variety‐not‐stated) accessions were found to be highly variable for winter survival. Seed derived from Minnesota was generally winter hardy (>65% survival), and seed from Oregon was not (<39%). Due to large variation among and within field environments, a method of controlled freezing was developed to supplement winter hardiness evaluations. No differences in freezing tolerance were found among accessions without cold acclimation. However, large differences in freezing tolerance occurred when plants were first grown for 2 wk in greenhouse conditions (22°C, 16‐h photoperiod) and then cold acclimated for 4 wk (3°C, 10‐h photoperiod). Lethal temperatures were determined from six 24‐h programmed freezing treatments, where treatment temperatures ranged from −13 to −21°C. Accessions differed significantly for freezing tolerance, with median lethal temperature values ranging from −8.4 to −16.0°C. This method of controlled freezing correlated highly with winter survival in field evaluations (ρ = 0.77).
Core Ideas Early‐season biomass is conventionally phenotyped by subjective visual estimates. RGB image data are highly predictive of biomass in hairy vetch breeding plots. Lidar and RGB image data can be combined to accurately predict sward biomass. Remote sensing could increase genetic gain potential for biomass in cover crops. Hairy vetch (Vicia villosa Roth) is an annual legume grown as a forage and cover crop. To improve cover crop function, traits such as biomass production are of high interest for cover crop breeders. However, direct phenotypic methods for biomass production are destructive. Breeders have thus relied on subjective, visual scoring of biomass, which is generally correlative but not quantitative or absolute. We evaluated two low‐cost remote sensing tools, lidar and red–green–blue (RGB) image analysis, for their potential to predict biomass in vivo. We evaluated these tools in two common forage breeding scenarios, spaced‐plant and sward‐plot nurseries, at three Minnesota locations following the winter of 2016–2017. Ground cover from RGB image binarization had a significant and linear relationship with aboveground biomass in spaced plants (R2 = 0.93) and sward plots (R2 = 0.89). However, once the image area from sward plots became saturated with vegetative pixels, a near‐exponential relationship would occur. Because of the prostrate growth habit of hairy vetch, RGB image analysis was more appropriate at lower plant densities, such as spaced‐plant nurseries. Conversely, the dimensionality of lidar sensing gave it greater predictive ability at higher plant densities where RGB analysis could not detect vertical increases in biomass. Lidar measures of sward‐plot height were also linearly and strongly related to dry‐matter biomass in sward plots (R2 = 0.80). When we combined RGB and lidar data to predict sward‐plot biomass in a multiple mixed‐effect regression model, we were able to explain more biomass variation than with the use of either phenotypic tool as a single predictor (R2 = 0.94).
Perennial ryegrass (PR) is a quality and high yielding forage that tends to lack winter hardiness to persist in the upper Midwest. The objective was to evaluate yield, stand persistence, forage nutritive value, and preference of experimental populations of winter hardy PR grown in monoculture and in mixture with white clover under livestock grazing. Research was conducted in St. Paul and Grand Rapids, MN. Meadow fescue (MF), tall fescue (TF), orchardgrass (OG), a reference PR, and two experimental populations of PR were grazed every 32 days by either horses (St. Paul) or cow-calf pairs (Grand Rapids). Prior to grazing, forage yield and quality samples were collected, and post-grazing, fields were visually assessed for the percentage of forage removal to determine preference. Yields of all PR (6.9 to 7.6 Mg ha −1) were similar, but lower compared to other coolseason grasses (CSG). Persistence was similar among all CSG in St. Paul; however, it was lower for all PR in Grand Rapids compared to other CSG. All PR were highly preferred by both horses (≥74% removal) and cattle (≥70% removal) and were consistently among the highest for crude protein (CP; 200 g kg −1), equine digestible energy (DE; 2.35 Mcal kg −1) and bovine metabolizable energy (ME; 2.6 Mcal kg −1), moderate for nonstructural carbohydrates (NSC; 136 g kg −1), and among the lowest for neutral detergent fiber (NDF; 518 g kg −1). Experimental populations of PR produced forage of high nutritive value, but yield and stand persistence may be less compared to other CSG at some locations. 1 INTRODUCTION Cool-season perennial grasses (CSG) are the foundation of productive pastures in the upper Midwest (Allen, Sheaf
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