Seed production in weedy Setaria spp.-gp

Seeds from Setaria faberi, S. viridis and S. pumila panicles in three Iowa crop fields were collected for the entire reproductive period. Seed number, panicle length, and seed number per panicle length varied among species, panicle types and sites. Greater numbers of seed per plant and per panicle were observed than previously reported. Setaria seed rain exhibited some stable, and many more plastic, responses. S. faberi panicles were consistently longer than those of S. viridis. S. viridis parameters were greater than S. pumila. Earlier panicles were greater than, or similar to, later ones for all parameters. More typically, tillers and panicles responded to local conditions in a plastic way, confounding the formulation of seed production generalizations. In S. faberi and S. viridis no consistent relationship between seed number and panicle length was observed among different tiller types. A more consistent relationship between parameters was observed for S. pumila compared to the others, making prediction possible for this species. The stability and plasticity of these relationships is partially due to the differences in S. faberi and S. viridis panicle, fascicle and spikelet morphology compared to S. pumila. These stable and plastic responses provide fine-scale adjustment to a locality, maximizing exploitation of local opportunity

Setaria faberi Seed Heteroblasty Blueprints Seedling Recruitment: II. Seed Behavior in the Soil

The fate of heteroblastic Setaria faberi seed entering the soil post-abscission is elucidated. Introduction of four populations of S. faberi seeds with heterogeneous dormancy capacities into the soil of a no-till Glycine max field resulted in the formation of enduring pools with varying cycles of dormancy, after-ripening, germination, dormancy reinduction and death. The buried seed rain of these highly dormant seed after-ripened with time and became highly germinable, awaiting favourable temperature and moisture conditions: the heterogeneous germination candidate pool. As this pool was depleted in the spring and early summer by seedling emergence and death, dormancy was re-induced in the living seeds that remained in the soil. These seeds remained dormant throughout the summer, then resumed after-ripening during late autumn. This dormancy-germinability cycle exhibited complexity both within and among S. faberi populations. Seed heteroblasty within S. faberi populations was retained, and germinability responses to the yearly seasonal environment varied among S. faberi populations. Further, local adaptation was shown by the differential germinability responses among S. faberi populations in common location agricultural nurseries. Seed mortality patterns also exhibited complexity within and among populations. Within an individual S. faberi population, mortality patterns changed as seeds aged in the soil. Among S. faberi populations differential mortality responses were observed in response to yearly seasonal environments and common nurseries. Observations of both germinability cycling and mortality are consistent with the hypothesis that S. faberi seed behaviour in the soil is predicated on dormancy capacity heterogeneity at abscission and modulated by the seasonal environmental conditions experienced in the field. The observations of seed fates obtained from heteroblastic seeds of four S. faberi populations buried at two common nurseries utilized a “bare core” technique. Cores were extracted periodically to determine seed fates. Inevitably, the fates of a fraction of those seeds could not be determined and were thus classified as unknown. Despite the equivocal nature of the unknowns they provided evidence that unaccounted seed losses were most likely not due to migration out of the core area. The lack of migration and high seed recovery (approximately 88.5%) emphasized the utility of the bare core technique in comparison to enclosed seed-soil cores

Weed Seedbanks of the U.S. Corn Belt: Magnitude, Variation, Emergence, and Application

Seedbanks and seedling emergence of annual weeds were examined in arable fields at eight locations in the Corn Belt. Seed densities were estimated by direct seed extraction from each of several soil cores in each sampled plot. Average total seedbank densities ranged from 600 to 162 000 viable seed m⁻² among locations. Coefficients of variation (CV) typically exceeded 50%. CV for seed densities of individual species usually exceeded 100%, indicating strongly aggregated distributions. CV were lower for species with dense seed populations than those with sparse seed populations. Variance of total seedbank densities was unstable when \u3c 10 cores were examined per plot, but stabilized at all locations when ≥ 15 cores were analyzed, despite a 12-fold difference in plot size and 270-fold difference in seed density among locations. Percentage viable seed that emerged as seedlings in field plots ranged from \u3c 1% for yellow rocket to 30% for giant foxtail. Redroot pigweed and common lambsquarters were the most frequently encountered species. Emergence percentages of these species were related inversely to rainfall or air temperatures in April or May, presumably because anoxia and/or high temperatures induced secondary dormancy in nondormant seed. From 50 to 90% of total seed in the seedbank were dead. This information can be employed by bioeconomic weed management models, which currently use coarse estimates of emergence percentages to customize recommendations for weed control

Setaria faberi Seed Heteroblasty Blueprints Seedling Recruitment: I. Seed Dormancy Heterogeneity at Abscission

Studies were conducted to determine the relationship between weedy Setaria faberi seed dormancy and subsequent behaviors in the soil culminating in seedling recruitment.This is the first in a series of three articles demonstrating weedy Setaria seed dormancy capacity heterogeneity at abscission (seed heteroblasty) provides a “blueprint” for those subsequent behaviours. The objective for this present article was to provide a robust characterization of seed heteroblasty at the time of dispersal for 39 locally adapted S. faberi populations, as influenced by parental genotype (time of embryogenesis) and environment (year, location). The heteroblastic structure of each population was revealed by the germination response to increasing amounts of after-ripening (in “ideal” conditions). The majority of the populations were differentiated from each other; this variation indicated a fine scale adaptation to different local environments.Taken together, the 39 responses represented Setaria’s “seed dormancy phenotype space” and revealed three different generalized dormancy patterns. The first pattern, low dormancy populations, had high initial germination in response to low doses of after-ripening. The second, high dormancy populations, had no or low initial germination with little additional response to increased after-ripening. Most populations had the third pattern, intermediate to the others, with low initial germination and increasing germination with increasing after-ripening dose. Germination responses were also used to rank populations based on their dormancy level to facilitate later comparisons with emergence behavior. Heteroblasty at abscission, elucidated herein, is hypothesized to influence subsequent seed fates in the soil, the focus of the next two articles in this series