Cup plant ( Silphium perfoliatum L.) has demonstrated potential for biomass production in studies using transplants in poorly drained cropland not suitable for conventional crops, but little is known about its establishment from seeding. The success rate for stand establishment of perennial plants is usually positively correlated with seed weight. Therefore, objectives of this study were to determine contribution of genetic effects to variation in achene weight, seed weight, achene length, and achene width of cup plant in a population with high biomass potential. Seedlings of 33 half-sib (HS) families were transplanted at Brookings, SD in 1999 and 2010. Achene/seed traits were determined at seed maturity in 2000, 2011 and 2012. Narrow-sense heritability was higher for achene weight and seed weight than that for dimensional achene traits. Within-population genetic variation occurred for achene and seed weight, both of which varied in response to temporal variation in precipitation and temperature. Results of this study indicated the presence of sufficient additive genetic variation for progress from among-family selection for achene weight. Thus, since families with heavy achenes had higher percent seedling emergence and superior seedling vigor compared to families with light achenes, achene weight may be useful for indirect selection for enhanced seed quality in development of new cultivars of cup plant for biomass production on marginal crop land.
Cup plant (Silphium perfoliatum L.) is a perennial dicotyledonous plant that occurs in moist prairie areas from Ontario to South Dakota and south to Georgia, Mississippi, Missouri, and Oklahoma [
Cup plant is recognized as a bio-diversity enhancing and pollinator attracting plant but may also have medicinal and soil remediation uses [
and the relationship between achene weight and seedling vigor, an important trait for stand establishment of perennial grasses and forbs (
The relationship between achene size and germination rate has been documented for several members of the Asteracae [
In general, expanding the agronomic and genetic information on cup plant is important as it has shown potential as an alternative forage crop and a dedicated bioenergy crop [
The cup plant population used for this genetic study was composed of progenies of 33 parental plants derived from bulk seed produced by putative random mating among several plants from each of natural populations from Minnesota and Illinois [
Experiment 1: Heritability using parent-offspring regression method
This first experiment was conducted during 1998 through 2000. Seedlings of the 33 HS families derived from seed produced in 1998 on the parental plants in the aforementioned polycross nursery were planted in replicated
spaced-plant nurseries at Aurora (N 44.28˚, W 96.68˚) and Brookings (N 44.31˚, W 96.80˚), SD in May 1999. Soils were an Estelline silt loam (fine-silty over sandy or sandy-skeletal, mixed, superactive frigid calcic hapludolls) at Aurora and a Vienna (fine-loamy, mixed, superactive, frigid, calcic hapludolls)-Brookings (fine-silty, mixed, superactive, frigid pachichapludolls) complex. A randomized complete block design was used with three replicates of single-row plots composed of 5 plants with 0.8-m intra-plot spacing and 2.1-m inter-plot spacing (i.e., about 6300 plants ha−1) at both Aurora and Brookings. In 2000 bulk seed was collected at maturity from each family row at each of the two locations. The Wisconsin check population was not included in this first experiment. Seeds were removed from achenes by hand using forceps. Weights of 25 achenes and their associated 25 dehulled seeds were determined for each family row by an electronic balance with 0.001 g accuracy. Individual-achene length and width were measured using a Digimatic caliper with 0.1 mm accuracy. Family means, averaged across locations, for achenes/seeds produced in 2000 were regressed on their respective female parental means for achenes/seeds produced in 1998 to obtain estimates of narrow-sense heritability for the four achene/seed traits.
Experiment 2: Heritability using variance components method
The second experiment was conducted during 2011 and 2012 on the South Dakota State University Experimental Station Felt Farm near Brookings, SD (44˚19'N and 96˚42'W). The soil was a McInotsh (fine-silty, mixed, superactive, frigid aquiccaldiudolls)-Badger (fine, smectitic, frigid verticargiaquolls) silty clay loam. Precipitation data were obtained for each of the growing seasons for 2011, 2012, and 2013 at Brookings (
This experiment employed narrower inter- and intra-plot spacing than did the first experiment. Individual family plots were single rows composed of six plants with 0.9 m between rows and 0.4 m between plants within rows (i.e., about 28,000 plants ha−1) [
The number of heads containing mature seeds collected from each family row varied from about 5 heads in 2012 to >10 heads in 2011. The growing season of 2011 was highly suitable for seed production and >100 heads were produced for each family row; whereas, in 2012 drought (
Experiment 3: Germination/seedling emergence and vigor
In addition to the above mentioned genetic studies for estimating narrow-sense heritability for achene traits, an additional experiment to measure germination in the laboratory and seedling emergence and seeding vigor was conducted in the greenhouse.
The seed germination experiment was carried out at the South Dakota State University Seed Testing Lab. Three replicates of 25 achenes for each family produced from family rows in 2011 were planted on top of blot-
Month | ||||||
---|---|---|---|---|---|---|
Year | April | May | June | July | August | September |
2010 | 31 | 56 | 202 | 134 | 121 | 188 |
2011 | 33 | 111 | 85 | 106 | 34 | 2 |
2012 | 59 | 161 | 43 | 31 | 50 | 11 |
2013 | 34 | 66 | 125 | 81 | 36 | 36 |
†South dakota climate and weather (http://climate.sdstate.edu/climate_site/archive_data.html).
ters in covered plastic germination boxes in a germination chamber set at constant 20˚C in November 2013, using the Association of Official Seed Analysts [
Concurrent with the planting of the germination component, three replicates of single rows 30 cm long containing 20 equidistant seeds with 8 cm between rows were planted for each family in galvanized metal flats in the greenhouse at Brookings, SD. The planting medium was Miracle-Gro® Micromax potting mix. Achenes were planted at a depth of about 2 cm. Air temperature in the greenhouse fluctuated from about 10˚C during night to occasionally >30˚C during day in response to ambient atmospheric conditions, such as variation in cloudiness. Completely randomized designs were used both in the greenhouse and South Dakota State University Seed Testing Lab.
A seed was considered to be germinated when a radicle emerged. A seedling was considered emerged when the cotyledons appeared above the soil. Numbers of germinated seeds in the lab and emerged seedlings in the greenhouse were recorded daily from eight through 14 days after planting. Up to ten seedlings per family per replication were harvested on day 14 for the greenhouse experiment. Seedlings were dried at 60˚C for 72 hours to determine biomass production seedling−1. Seedling vigor was determined using a modified approach to the method described by Abdul-Baki and Anderson [
Analyses of variance were performed to determine genetic and environmental effects for field experiments and for genetic effects for the greenhouse experiment using Statistix 9 [
The formula for calculating narrow-sense heritability [
where
Significant differences were found among the 33 parental plants in the polycross nursery and among the 33 families in the HS family nursery for all four of the achene/seed traits (ANOVA not shown). The range in parental means for 25-achene weight from achenes produced in 1998 in the polycross nursery was from 0.344 to 0.600 g. The range in family means from seed produced in 2000 was from 0.239 to 0.391 g.
The growing season of 2011 was relatively wet and cool compared to that of 2012. The average temperatures during June (18˚C) and July (24.3˚C) of 2011 were 3.3˚C and 1.0˚C lower than those in 2012. Total precipitation for June through August during flowering, pollination, and seed production was 225 mm in 2011 and 124 mm in 2012 (
Significant differences were found between years for all four of the achene traits. All of the achene traits were substantially reduced in 2012 compared to 2011. Family differences were found for achene weight and seed weight. The family × year interaction was significant for all four traits (
Means for the 34 entries (33 HS families and a check population) for seed weight ranged from 0.186 to 0.323 g in 2011 and from 0.150 to 0.253 g in 2012; for achene length entry means ranged from 8.0 to 9.6 mm in 2011 and from 5.7 to 8.7 mm in 2012; and for achene width entry means ranged from 5.4 to 6.5 mm in 2011 and from 3.1 to 5.5 mm in 2012 (
Coefficients of variation were higher for all traits in 2012 than those in 2011, except for seed weight (
Significant genetic correlation coefficients were detected for all pairings of the four achene/seed traits (
Highly significant year effects indicated phenotypic plasticity for achene/seed traits in response to temporal variation in environmental conditions (
Significant differences were found among families for percentage seedling emergence, dry seedling weight, and the seedling vigor index. Means among 34 families ranged from 70% to 98.3% for emergence and from 19.8 to 69.2 for the seedling vigor index, respectively. Emergence percentage increased as achene weight increased. Seven out of the top nine families for percent seedling emergence had greater than 90% emergence. In general, families with heavy achenes had higher percentage emergence and produced larger seedlings with greater seedling vigor than families with relatively light achenes (r = 0.76 and 0.81, respectively). Germination rate was low at constant 20˚C in a germination chamber, using the AOSA protocol for annual sunflower. After 14 days, 25% of the 34 entries had no germination, whereas 75 % had germination that ranged from 5% to 20%.
The present research is the first agronomic study conducted on genetic variation for seed-related traits within the genus Silphium and, for that matter, as far as we know, for other perennial species within the family Asteraceae.
Source of variation | DF | AW | SW | AL | AWD |
---|---|---|---|---|---|
Year (Y) | 1 | 0.42580** | 0.09368** | 160.751** | 129.251** |
Rep (R) | 2 | 0.01970** | 0.00488** | 2.674** | 2.365** |
Family (F) | 33 | 0.00992** | 0.00349** | 1.457 | 0.885 |
Y × R | 2 | 0.00053 | 0.00084 | 0.32 | 0.264 |
F × Y | 33 | 0.00205** | 0.0010** | 0.985** | 0.666** |
F × R | 66 | 0.00276** | 0.00068* | 0.293 | 0.261 |
Error | 66 | 0.00098 | 0.00041 | 0.277 | 0.268 |
*, **Significant at 0.05 or 0.01 probability level, respectively.
Achene weight (g) | Seed weight (g) | ||||||
---|---|---|---|---|---|---|---|
Family | 2011 | Family | 2012 | Family | 2011 | Family | 2012 |
F29 | 0.466 | F20 | 0.364 | F12 | 0.323 | F12 | 0.253 |
F33 | 0.435 | F33 | 0.361 | F27 | 0.315 | F27 | 0.226 |
F27 | 0.433 | F25 | 0.339 | F21 | 0.309 | F31 | 0.225 |
F31 | 0.417 | F29 | 0.336 | F33 | 0.284 | F33 | 0.223 |
F12 | 0.412 | F18 | 0.335 | F29 | 0.28 | F18 | 0.221 |
F25 | 0.408 | F31 | 0.334 | F20 | 0.279 | F29 | 0.22 |
F13 | 0.401 | F27 | 0.328 | F13 | 0.266 | F13 | 0.218 |
F20 | 0.398 | F12 | 0.318 | F19 | 0.264 | F20 | 0.218 |
F7 | 0.395 | F13 | 0.315 | F7 | 0.263 | F23 | 0.217 |
F2 | 0.393 | F22 | 0.31 | F16 | 0.263 | F18 | 0.215 |
F8 | 0.392 | F26 | 0.305 | F18 | 0.256 | F19 | 0.213 |
F6 | 0.389 | F23 | 0.297 | F5 | 0.254 | F28 | 0.212 |
F21 | 0.379 | F28 | 0.295 | F14 | 0.253 | F7 | 0.212 |
F18 | 0.377 | F7 | 0.293 | F21 | 0.253 | F22 | 0.211 |
F3 | 0.377 | F16 | 0.279 | F30 | 0.252 | F26 | 0.21 |
F19 | 0.369 | F19 | 0.278 | F2 | 0.251 | F16 | 0.207 |
F16 | 0.366 | F21 | 0.277 | F11 | 0.25 | F30 | 0.203 |
F4 | 0.364 | F5 | 0.267 | F6 | 0.249 | F21 | 0.202 |
F30 | 0.362 | F24 | 0.264 | F3 | 0.244 | F9 | 0.202 |
F24 | 0.358 | F30 | 0.264 | F22 | 0.24 | F14 | 0.202 |
F5 | 0.357 | F8 | 0.258 | F25 | 0.234 | F24 | 0.201 |
F14 | 0.352 | F14 | 0.257 | F9 | 0.231 | F17 | 0.198 |
F22 | 0.352 | F17 | 0.256 | F23 | 0.225 | F5 | 0.197 |
F26 | 0.349 | F4 | 0.246 | F4 | 0.224 | F2 | 0.195 |
F9 | 0.346 | F2 | 0.245 | F28 | 0.222 | F8 | 0.193 |
F11 | 0.346 | F9 | 0.244 | F8 | 0.22 | F6 | 0.191 |
F23 | 0.344 | F6 | 0.23 | F24 | 0.219 | F32 | 0.191 |
F28 | 0.342 | F15 | 0.229 | F10 | 0.215 | F11 | 0.188 |
F17 | 0.319 | F32 | 0.225 | F26 | 0.21 | F4 | 0.186 |
F15 | 0.299 | F11 | 0.225 | F32 | 0.207 | F15 | 0.185 |
F1 | 0.295 | F10 | 0.215 | F17 | 0.198 | F10 | 0.179 |
F10 | 0.295 | F3 | 0.181 | F15 | 0.193 | F3 | 0.152 |
F32 | 0.286 | F1 | 0.177 | F1 | 0.186 | F1 | 0.15 |
Check | 0.368 | check | 0.285 | check | 0.229 | check | 0.19 |
Mean | 0.369 | 0.277 | 0.246 | 0.203 | |||
LSD(0.05) | 0.06 | 0.05 | 0.044 | 0.029 | |||
CV (%) | 12.5 | 14.4 | 11 | 8.9 |
Achene length (mm) | Achene width (mm) | ||||||
---|---|---|---|---|---|---|---|
Family | 2011 | Family | 2012 | Family | 2011 | Family | 2012 |
F13 | 9.6 | F15 | 8.67 | F2 | 6.56 | F32 | 5.55 |
F12 | 9.41 | F12 | 8.35 | F29 | 6.46 | F16 | 5.43 |
F3 | 9.4 | F20 | 8.09 | F8 | 6.39 | F20 | 5.22 |
F33 | 9.24 | F18 | 8.08 | F12 | 6.36 | F12 | 5.21 |
F31 | 9.15 | F29 | 8.05 | F3 | 6.33 | F18 | 5.13 |
F21 | 9.15 | F26 | 8.01 | F19 | 6.32 | F25 | 5.13 |
F27 | 9.06 | F25 | 8 | F25 | 6.23 | F27 | 5.09 |
F2 | 9.02 | F2 | 7.98 | F33 | 6.23 | F29 | 5.09 |
F29 | 9.01 | F22 | 7.52 | F26 | 6.21 | F10 | 5.08 |
F15 | 9 | F6 | 7.5 | F13 | 6.19 | F26 | 5.05 |
F7 | 9 | F27 | 7.44 | F31 | 6.18 | F8 | 5.03 |
F16 | 9 | F10 | 7.36 | F20 | 6.17 | F5 | 4.97 |
F6 | 8.96 | F16 | 7.31 | F30 | 6.15 | F22 | 4.86 |
F25 | 8.93 | F32 | 7.23 | F21 | 6.11 | F33 | 4.76 |
F8 | 8.88 | F4 | 7.22 | F27 | 6.11 | F31 | 4.68 |
F30 | 8.88 | F31 | 7.12 | F7 | 6.04 | F2 | 4.63 |
F18 | 8.85 | F7 | 7.08 | F32 | 6.02 | F4 | 4.43 |
F26 | 8.85 | F33 | 7.05 | F24 | 6.02 | F23 | 4.41 |
F24 | 8.81 | F30 | 7.03 | F23 | 6.02 | F15 | 4.12 |
F19 | 8.75 | F13 | 7.02 | F1 | 5.97 | F17 | 4.01 |
F9 | 8.75 | F23 | 6.64 | F16 | 5.93 | F28 | 3.92 |
F17 | 8.6 | F17 | 6.51 | F22 | 5.92 | F14 | 3.92 |
F22 | 8.59 | F8 | 6.45 | F6 | 5.89 | F19 | 3.9 |
F11 | 8.57 | F1 | 6.45 | F5 | 5.87 | F9 | 3.9 |
F32 | 8.56 | F24 | 6.37 | F15 | 5.82 | F11 | 3.89 |
F20 | 8.48 | F19 | 6.29 | F4 | 5.82 | F30 | 3.89 |
F23 | 8.47 | F28 | 6.1 | F18 | 5.79 | F1 | 3.88 |
F14 | 8.45 | F3 | 6.07 | F17 | 5.69 | F13 | 3.88 |
F5 | 8.28 | F5 | 5.94 | F14 | 5.68 | F24 | 3.82 |
F28 | 8.25 | F9 | 5.91 | F9 | 5.66 | F3 | 3.72 |
F4 | 8.25 | F14 | 5.85 | F28 | 5.63 | F21 | 3.44 |
F1 | 8.23 | F21 | 5.84 | F11 | 5.6 | F6 | 3.32 |
F10 | 8.01 | F11 | 5.7 | F10 | 5.45 | F7 | 3.07 |
check | 8.99 | check | 6.85 | check | 5.97 | check | 4.22 |
Mean | 8.81 | 7.03 | 6.02 | 4.43 | |||
LSD(0.05) | 0.64 | 1 | 0.52 | 1.1 | |||
CV (%) | 4.5 | 9.1 | 5.3 | 14.7 |
LSD = Least significant different; CV = coefficient of variation.
Trait | AW | AL | AWD |
---|---|---|---|
AL | 0.67** | ||
AW | 0.59** | 0.71** | |
SW | 0.82** | 0.49** | 0.45** |
*, **Significant at 0.01 level of probability.
Trait | Variance components | Parent-offspring regression | ||
---|---|---|---|---|
Achene weight | 0.65 (0.32)† | 0.68 (0.23) | ||
Achene length | 0.32 (0.13) | 0.40 (0.14) | ||
Achene width | 0.25 (0.11) | 0.37 (0.12) | ||
Seed weight | 0.66 (0.26) | 0.69 (0.24) |
†Standard error of heritability estimate (Hallauer and Miranda, 1988).
Traits | ||||
---|---|---|---|---|
Year | AW (g) | SW (g) | AL (mm) | AWD (mm) |
2011 | 0.369**† | 0.246** | 8.8** | 6.0** |
2012 | 0.277 | 0.203 | 7.0 | 4.4 |
†F-test of difference between annual means significant at the 0.01 level of probability.
Therefore, the only published studies that are useful for drawing analogies between cup plant and related species are necessarily those conducted on cultivated annual sunflower, for which there are numerous genetic studies on seed size/weight and correlated traits. Several of those studies are useful for understanding the importance of genetic and environmental impacts on achene/seed weight in cup plant, relative to an important crop plant belonging to the Asteraceae family.
The impact of temporal variation in growing conditions was highly evident for achene/seed traits in cup plant. The environmental conditions during summer 2011 were much more favorable than in 2012 [
Significant family × year interactions for achene weight and associated traits indicated that these 33 HS families did not rank the same across years. However, the relatively consistent performance of the top 25% of the families between years for achene and seed weights suggested that progress from selection for mean achene/seed weight could be expected in normal rainfall as well as drought stressed environments. Kwon and Torrie [
Moderate narrow-sense heritability estimates obtained for achene and seed weight from both variance components and parent-offspring regression methods indicated additive genetic variance was a significant fraction of the total phenotypic variance. Additive genetic variance also accounted for most of the genetic variance for seed weight in sunflower [
Significant associations between achene weight and germination percentage and seedling dry weight suggested that achene weight may be an important indirect selection criterion for improving stand establishment in cup plant. Numerous other studies of dicotyledonous plants have pointed out a positive relationship between seed size and germination success [
High positive genetic correlations for achene/seed traits were similar to those for seed yield traits in sunflower reported by Habib et al. [
As expected from the wide environmental variation between 2011 and 2012, most families showed highly plastic responses in achene/seed traits to temporal variation, with reduced expression in 2012, the drought year, compared to 2011. However, several families with similar means between years suggested genetic variation for type of response to large variations in environmental conditions for seed-related traits within this population of cup plant.
The large difference between Experiments 1 and 2 for plant population density was related to different objectives for each experiment reported here and to population densities in previous studies on cup plant successfully conducted in the Midwest. Experiment 1 was intended to evaluate the potential of individual plants within family rows to express their potential for biomass production, similar to previous studies in Wisconsin (K.A. Albrecht, personal communication). Whereas, Experiment 2 was intended to identify half-sib families that had the potential for biomass production in a planting density and arrangement similar to that used for commercial production of confectionary sunflowers in the northern Great Plains. In other words, for Experiment 1 the intended unit of selection was an individual plant, whereas for Experiment 2, the intended unit of selection was a half-sib family. More research is needed to determine the optimum plant population density for biomass and seed production in cup plant in North America. Preliminary data from on-going trials in South Dakota and Wisconsin have indicated that biomass response to variation in plant density is not independent of environment (K. Albrecht and A. Boe, unpublished data, 2014). Past studies with sunflower have shown increases in seed yield and decreases in seed weight in response to increases in plant population density [
Germination of cup plant seeds can be delayed due to dormancy, especially from seed planted within a year or two after harvest (Boe, unpublished data). However, in our study >70% of seeds of each family produced in the field in 2011 germinated under greenhouse conditions in 2013, suggesting that exposing cup plant seeds to wide ranges in diurnal temperatures and sunlight intensity, such as those that occurred in the greenhouse, might trigger germination. The positive linear relationships between seed weight and seedling emergence and seedling weight found in the present study have also been reported for sunflower [
In summary, achene/seed traits in cup plant proved useful for quantifying among-family genetic diversity and phenotypic plasticity in fitness-related traits, as well as potential selection criteria to improve stand establishment. Of course, field studies are needed to determine if the genetic variation for seed related traits in this population is useful for developing new populations with improved agronomic performance related to seedling vigor and other agronomic traits. In addition, since annual variation in precipitation was shown to have a large impact on achene/seed weight (e.g., 2011 and 2012 seed crops), the potential influence of such environmentally-in- duced phenotypic variation on agronomic performance [
This research was supported by funding from the North Central Regional Sun Grant Center at South Dakota State University through a grant provided by the US Department of Energy Bioenergy Technologies Office under award number DE-FG36-08GO88073 and 08GO88073 and US Department of Agriculture award number 2010-38502-21861. We express appreciation to USDA-NIFA Hatch project 1005459 for providing funding for this research through the South Dakota Agricultural Experiment Station. Appreciation is also expressed to Dr. Brent Turnipseed and Mr. Dennis Ruhlman for providing facilities and expertise for the laboratory germination study.