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Supplement of heteroembryonic seedlings of Setaria seeds: ⅰ. Heterogeneity of seed dormancy during abscission

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  • Save International Journal of Plant Research 2012, 2(3): 46-56 DOI: 10.5923/j.plant.20120203.01 Setariafaberi Seed HeteroblastyBlueprints Seedling Recruitment: I. Seed Dormancy Heterogeneity at Abscission K. Jovaag1, J. Dekker2,*, B. Atchison2 1Weed Biology Laboratory, Department of Agronomy, Department of Statistics, Iowa State University, Ames, Iowa, 50011, USA 2Weed Biology Laboratory, Department of Agronomy, Iowa State University, Ames, Iowa, 50011, USA Abstract Studies were conducted to determine the relationship between weedy Setariafaberi seed dormancy and sub- sequent 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 Keywords SeedHeteroblasty, Seed Dormancy, Seed Fate, Seedling Recruitment, Setaria, Seed Dispersal 1. Introduction The relationship between seed dormancy induced by parent Setaria plants at the time of abscission is rationalized herein with subsequent behaviours in the soil and seedling recruitment.Evidence provides strong inferences that heterogeneous dormancy among Setaria seeds at abscission is an important determinant of subsequent behaviours of individuals in the soil leading to the timing of recruitment. The timing of seedling recruitment of an individual relative to that of neighbour plants is one of the most important determinants in plant community assembly and its consequential composition and structure.The importance of recruitment timing is especially crucial in agricultural habitats characterized by frequent, profound disturbance regimes (e.g tillage, herbicides, harvesting) in which theentireplant community is typically removed on an annual basis. * Corresponding author: (J. Dekker) Published online at Copyright © 2012 Scientific & Academic Publishing. All Rights Reserved Knowledge of recruitment timing relative to crop emergence is crucial to weed management, particularly foreffective use of control tactics (e.g. tillage, herbicides). The first phases of the weedy Setaria plants' life history are therefore of critical importance, especially those temporally expressed traits of seed dormancy, germinability, germination and seedling emergence. Foxtails (Setaria speciesgroup) are one of the worst weed groups interfering with U.S. and world agriculture and land management (Dekker 2003, 2004), and therefore one of the world’s most successful colonizing plants. Setariafaberi is a recent invasive to North America, infesting large areas of the U.S. corn belt. S. faberi is an ideal species with which to study seed life history: globally it is nearly identical genetically (Wang et al., 1995). One important trait is the production and dispersal of heterogeneous seed (Dekker & Hargrove, 2002; Dekker et al., 1996).Heterogeneity of dormancy among seed from a single parent plant, seed heteroblasty, is one of several types of heteroblastic development of repeating plant units (metamers) during plant ontogeny (Gutterman, 1996; Jones, 1999). This phenomenon has been characterized in other International Journal of Plant Research 2012, 2(3): 46-56 47 plant species (e.g. Xanthium pensylvanicum, Weaver & Lechowicz, 1983; Chenopodium album, Williams & Harper, 1965).Systematic, quantitative characterization of heteroblasty among individuals within a locally adapted population, between local populations, and their relationship tosubsequent life history behaviours has not been reported previously. An individual weedy Setaria spp. plant synflorescence produces individual seeds whose germination requirements vary.This seed heteroblasty occurs in any parental environment, even those within controlled, constant conditions for the duration of its life history (Dekker, et al., 1996; Harr, 1998).Seed heteroblasty is therefore a constitutively expressed genetic (or epigenetic) trait.The dormancy capacity of a individual S. faberi seed refers to its dormancy state at abscission, as well as the quantity of environmental signals (oxy-hydro-thermal time; Dekker et al., 2003) required to stimulate a change in state (e.g. after-ripening duration) (Dekker, et al., 1996; Dekker & Hargrove, 2002; Sareini, 1970).Germination capacity is an inherent quality of a Setaria seed which is retained for its entire life. The heteroblastic composition induced in an individual cohort of seeds is modulated by parental plant architecture and the environment during ca. 12 day embryogenic period. Earlier fertilized seeds produced on Setaria primary synflorescences (typically August in the midwest U.S.) are relatively more dormant than those from secondary synflorescences (ca. September), which are more dormant than seed on tertiary and subsequent synflorescences (ca. October) (Dekker, 2003).Hence, individual Setaria plant populations are most accurately defined as a unique combination of species, individual parent plant location and time of abscission (calendar Julian week (JW) and year). Seed heteroblasty inevitably leads to formation of longlived seed pools in the soil. A seed pool begins with heterogeneous dormant seed dispersed into the soil from local or distant plants. The seed can remain dormant in the soil, after-ripen, germinate, emerge as a seedling, or die. Past soil seed pool studies have relied on population-based models (e.g. Bekker, et al, 2000; Hoffman, Owen & Buhler, 1998; Roberts & Nielson, 1981; Williams & Harvey, 2002). Experimentally, they have described seed pools in terms of mean behaviours (e.g. number of seeds per unit area), vertical distribution, percent loss, species diversity, species richness, etc. These summary statistics obscure the individual behavioural patterns which underlie the population means, thus obscuring any relationship between the individual phenotype and its subsequent behaviour. Populationbased models are appropriate for quantifying differences among groups, but individually-based models are necessary to determine inferences of the relationship between heteroblasty and subsequent behaviour of a local population. The relationship between seed dormancy capacity and subsequent behaviours has not been previously demonstrated. A fundamental question in plant seed biology concerns the ecological role of seed dormancy and the quantitative relationship between seed heteroblasty and recruitment timing: does dormancy capacity influence subsequent behaviour? Therefore, the hypothesis for this series of articles is that heterogeneous germination requirements among S. faberi seed at abscission are a determinant of the subsequent behaviours of those individuals in the soil, including seedling recruitment timing. If seed heteroblasty can be quantified at abscission, can an empirical relationship between dormancy state at abscission and subsequent behaviours in the seed pool be shown? If so, the relationship between seed heteroblasty and subsequent behaviours may provide the hedgebet structure of seedling emergence timing.That is, heteroblasty is the “blueprint” for seedling recruitment. The heteroblastic differences among individuals of a specific population can be compared with other populations to reveal heterogeneous local adaptation across the landscape. These dormancy differences will be echoed in the pattern of seedling emergence, and evolve over time in their interaction with the changing environment. The experimental goal for this first paper is to quantify the heterogeneity in germination capacity among S. faberi populations at abscission. Thus seed was gathered from S. faberi populations that differed primarily in location, year and calendar time of collection to determine how these factors were related to germination capacity. The germination capacity of a group of individual seeds can be determined by subjecting them to increasing durations of after-ripening signals and comparing differences in percent germination among populations. If there is local adaptation, each population will have a unique germination response to increasing after-ripening. But are there general patterns among locally adapted populations? To examine this possibility, populations were grouped on the basis of their germination capacity. This paper characterizes the seed dormancy heterogeneity at abscission which is input into the soil. It is the first in a series of three papers on the dynamics of weedy Setaria soil seed pools. The second and third papers will examine seed in the soil and seedling emergence. 2. Materials and Methods 2.1. Experimental 2.1.1. Setaria Populations For this study, a Setaria population was defined to be a specific combination of location and seasonal time of abscission (Table 1).Seeds collected from the same location but at different seasonal times were treated as samples from different populations rather than repeated measures of the same population.The sampled populations consisted of individual seeds, not the parent plants from which they werederived.Seeds developing early in the season differ from those developing later in the season due to the strong influence of photoperiod (Dekker, 2004; Dekker et al, 1996). Locations.Two spatial criteria were used to select loca- 48 K. Jovaag et al.: SetariaFaberi Seed Heteroblasty Blueprints Seedling Recruitment: I. Seed Dormancy Heterogeneity at Abscission tions from which S. faberi seeds were collected. The primary criteria restricted populations to a local area around Ames, IA.Locations were all within 0º4’77” latitude and 0º4’5” longitude of each other (Table 1). Most (Johnson, Curtiss, Oakwood, Wessex and Whiteoak) were less than 3km from each other. The geographic range was restricted to allow characterization of a localized population phenotypic (heteroblastic) structure.A second criteria, used in 1999, was to collect from two distant locations in Iowa (near Crawfordsville, about 194km from Ames) to gain some initial perspective on regional variation. All seed were gathered from almost pure Setaria monocultures, with special care taken to ensure no contamination from non-target Setaria species occurred. When seed was collected from the same site in different years the site was protected from human interference. Seasonal time of abscission. Setaria seed development occurs continuously from July through November (Julian week (JW) 26-48) depending on environmental conditions. To evaluate the effects of time of abscission during this seed rain period, seed was collected at discrete intervals roughly corresponding to August (early; JW 31-35), September (middle; JW 35-39) and October (late; JW 40-44) (table 1). Our Julian week calendar assumes 29 days for every February. 2.1.2. Seed Collection and Preparation The following standard procedures were repeated each year to supply genetically pure, mature, high quality seed for experimentation. Seed collection. At the collection site, individual plants with mature synflorescences were identified by species. The seed heads were tapped against the wall of an empty plastic dishpan to dislodge the ripe seed. Ambient wind conditions in the field dislodge and disperse seeds from the parent plant soon after abscission (e.g., 0-5 days; Dekker et al., 1996). As such, the seed collected in these studies were recently abscised and represent the seed rain of that Julian week. Table 1. Location (name, latitude, longitude) and nomenclature (lot no., name) of S. faberi populations grouped by year of abscission and collection.1Population names consist of 3 parts: a prefix letter designating the population location, two digits designating the collection year, and two digits designating the Julian week of abscission and collection. All locations were in Ames, IA, except S.E. Research Station, near Crawfordsville, IA; R was 100m west of Hinds (H) Name 1997 Curtiss Farm Oakwood Drive Seed Collection Location 42o00'23"N 42°01'83"N 1998 Curtiss Farm 42o00'23"N Hinds Farm Johnson Farm Mortensen Road Wessex Road Whiteoak Drive 1999 Curtiss Farm Hinds Farm Johnson Farm S.E. Research Station S.E. Research Station Whiteoak Drive 41°58'88"N 42°00'57"N 41°59'67"N 41°59'75"N 42o00'23"N 41°58'88"N 41°12'36"N 41°12'26"N 3780K99-36 41°59'75"N Latitude 93o38'90"W 93°36'54"W 93o38'90"W 42°03'65"N 93°38'49"W 93°40' 59"W 93°38'30"W 93°38'90"W 93o38'90"W 42°03'65"N 93°38'49"W 91°29' 73"W 3767B99-36 91°29'68"W 93°38'90"W Population Nomenclature Longitude Lot # Name1 3728 C97-36 3732 O97-34 3733 O97-36 3734 O97-37 3740 3746 3754 93°36' 96"W 3739 3744 3747 3752 3738 3749 3751 3745 3750 3743 3758 3741 3748 3753 C98-32 C98-36 C98-40 H98-32 R98-34 H98-36 H98-40 J98-32 J98-36 J98-40 M98-34 M98-40 X98-34 X98-39 W98-32 W98-36 W98-40 3769C99-35 3770C99-38 3771C99-42 93°36' 96"W 3774H99-36 3775H99-41 3776J99-35 3777J99-38 3778J99-42 3766B99-32 3773H99-32 3768B99-40 3779K99-32 3781K99-40 3782W99-32 3783W99-36 3784W99-42 International Journal of Plant Research 2012, 2(3): 46-56 49 Seed preparation.Seed lots were dried separately on #16 (1.18 mm mesh openings) and or #18 (1.00 mm openings) soil separation sieves (Seedburo Equipment Co., Chicago, IL, 60607) to allow adequate airflow around the seed while preventing any accidental mixing of different seed lots.Seed lots were dried at room temperature (20℃) and ambient humidity for three to four days, stirred once per day. Once dry, the seeds were cleaned using a seed blower (Seedburo Equipment Co., Chicago, IL, 60607).This treatment removed any foreign particles leaving only hard, dark, mature seeds. The majority of these seeds were then used for dormancy and emergence experiments.A small portion of the seeds were placed into long-term storage at –20℃. After-Ripening Germination Assays. Primary dormancy can be experimentally determined by exposing freshly abscised seeds to after-ripening (AR) conditions for various time intervals, then removing them to conditions optimal for germination. After-ripening germination assays were conducted in 1998 and 1999 on seed collected in 1997-1999. Seeds collected in 1998 and 1999 were evaluated immediately after harvesting and processing. Seeds collected 1997 were stored at –20℃, then removed from those conditions and tested at the same time as the 1998 populations. Past experience indicates storage for one year at –20℃ results in some low levels of after-ripening, but it is a small effect that does not change the relative differences between stored populations (Thornhill, 1997).This storage is an artefact to be considered in interpreting the results obtained from 1997 in subsequent dormancy and emergence experiments. After-ripening environmental conditions. The general procedure for both years was as follows. A 60x15 mm glass culture Petri dish (Fisher Scientific Company, Pittsburgh, PA, 15275) was labelled with the seed lot number and treatment. Two disks of Anchor Blue germination blotter paper (Anchor Paper Co., St. Paul, MN, 55101), 51mm in diameter, were placed in the dish completely covering the bottom. Immediately prior to sealing the dishes, 2 ml (1998), or 3ml (1999) of distilled, de-ionized water was placed in the dishes along with 20 dry Setaria seeds. Preliminary studies showed similar germination responses over a wide range of water contents with dishes of this size (data not reported).The seeds were placed in a 5 x 4 grid on the germination paper to facilitate data collection. After arranging the seed, the dishes were immediately sealed by double-wrapping with Parafilm “M”  (American National Can, Chicago, IL, 60631) to prevent water loss. Five replicates (Petri dishes) of each treatment were then doublewrapped with aluminium foil to ensure complete exclusion of light, and then placed in constant 4℃ after-ripening conditions. In 1998, six treatments of 0-11 weeks of after-ripening (0, 14, 35, 49, 63, 77 days) were used. In 1999, 16 after-ripening treatments of 0-6.5 weeks (0, 3, 6, 9, 12, 15, 18, 21, 24, 27, 30, 33, 36, 39, 42, 45 days) were used. Seed germination evaluation. After the specified after-ripening period the aluminium foil was removed, and the Petri dishes were placed into a controlled environment seed germination cabinet (Model SG-30, Hoffman Manufactur- ing, Inc., Albany, OR, 97321) for eight days. The daily conditions in the germination chamber alternated between 16 hours of light at 30℃ followed by 8 hours of darkness at 20℃. After eight days each dish was removed, opened, and evaluated for germination percentage. A seed was considered germinated if the coleorhiza and/or coleoptile protruded outside the seed hull. 2.2 Analysis The focus of this study was to quantify the heterogeneity in germination capacity among Setaria populations which differ in the year, location, and seasonal time of seed collection. The effect of increasing after-ripening duration on percent seed germination was used to estimate the cumulative distribution of germination capacity within each individual population. Subsequent analysis was conducted to determine if there were general patterns of seed germination among populations in response to after-ripening duration. 2.2.1. Germination Capacity Heterogeneity of Individual Populations Heterogeneity between years. The results from each year (1997, 1998, 1999) were analyzed separately because the locations and Julian weeks during which seeds were collected in 1997, 1998 and 1999 differed, though there was some overlap. Also, the after-ripening durations differed in the assays conducted in 1998 and 1999.Thus seed germination capacity of 1997, 1998 and 1999 populations could not be formally compared, except within two small subsets of the data. First, Curtiss in JW 36 was common to both 1997 and 1998.Percent germination from these two populations was analyzed using year, after-ripening duration, and their interaction as factors. Second, four populations (Hinds, Whiteoak in JW 32, 34) were common to both 1998 and 1999, and three after-ripening durations (1998:14, 35, 49 days; 1999:15, 36, 45 days) were similar. Percent germination from this subset was analyzed using ANOVA with year, location, seasonal time of abscission, after-ripening duration and their interactions as factors. The effect of year was tested using replication, plus the interaction of replication and year, as the error term. All other factors and interactions were tested using the residual error. The balanced design and residual plots indicated ANOVA was appropriate for these data. Separate analyses were then conducted for each of the three after-ripening durations. Heterogeneity within years. Percent germination of populations collected within a year (1997, 1998, 1999) were analyzed separately using ANOVA with duration of afterripening, population (a combination of location and seasonal time of abscission), and their interactions as factors. Percent germination from each after-ripening duration longer than 3 days was then analyzed separately (using one-way ANOVA), which allowed testing of mean separation using Tukey’s multiple comparison tests. Data from 0 and 3 days of after-ripening were not analyzed as they consisted mostly of zeros and were thus not appropriate for 50 K. Jovaag et al.: SetariaFaberi Seed Heteroblasty Blueprints Seedling Recruitment: I. Seed Dormancy Heterogeneity at Abscission ANOVA as indicated by their residual plots. Data from 6-77 days of after-ripening was appropriate for ANOVA as indicated by the balanced design, residual plots and the large number of seeds used (5 replications of 20 seeds for each of the 39 populations). Heterogeneity within an after-ripening duration. The percent germination least squares means (LSmeans) for all populations within an after-ripening duration were compared using Tukey’s multiple comparison tests. The relationship between germination and seasonal time of abscission was investigated using contrasts comparing seed collected during the early (JW 32), middle (JW36), and late (JW40-42) periods of the seed rain. Only those locations that had seed collected at all three times were included in these contrasts to avoid bias from location differences. 2.2.2. General Patterns in Germination Capacity Patterns in population phenotypic structure of the Setaria seed evaluated herein were revealed at two, hierarchically linked levels of community organization: responses within individual populations to after-ripening duration and among populations across a varying landscape (local to regional).If general patterns exist, grouping individual populations with similar responses to after-ripening duration will provide a model of the population phenotypic structure at both levels. To accomplish this grouping, a clustering method was developed which began with ranking populations into groups within an after-ripening duration, then combined the results across durations to create a population grouping independent of after-ripening duration. Additionally, patterns among populations were utilized to link dormancy capacity and subsequent seedling emergence (Jovaag, Dekker & Atchison 2009b). Grouping of populations with similar phenotypic structures. A three part clustering method was developed to group populations. The first part, intra-AR grouping, ranked the populations into three groups based on the germination LSmeanswithin each after-ripening duration. The second part consisted of totalling each population’s intra-AR rank numbers across durations. The third part, inter-AR grouping, was contingent on the intra-AR rank totals and created the final population grouping which was independent of after-ripening duration. A detailed description of this clustering method can be found in Jovaag (2006). To reveal general patterns, the average percent germination within each after-ripening duration was calculated for each inter-AR group. The resulting curves were then smoothed using a degree three B-spline with two knots. Curves defined by the germination of individual populations were also smoothed to provide a schematic diagram of the relationship between after-ripening and germination. The effectiveness of this clustering procedure was examined by simulating a dataset so that the actual inter-AR group of each population was known, then subjecting it to the clustering procedure to determine the proportion of populations that were correctly classified. To simulate the dataset, ten binomial random samples of size 100 were ob- tained using each average percent germination of the inter-AR groups (from the actual data).The proportion of successes from each of those samples was then used to obtain 5 binomial random samples of size 20.This resulted in a simulated dataset representing 5 replications of 20 seeds from 10 populations for each inter-AR group. 3. Results 3.1. Germination Heterogeneity between Years Comparisons of S. faberi germination responses between years were made with the few populations (locations, Julian weeks) common to 1997-1998 and 1998-1999 seed. The germination response of 1997 and 1998 seed collected in the same location (Curtiss) and seasonal time (JW 36) depended on after-ripening (AR) duration (year*duration p-value=.0012). In general, germination of 1997 seed tended to be greater than the 1998 seed at 35 days of AR, but the 1998 seed was more germinable with longer AR durations (49 and 77 days of AR). Germination of 1997 and 1998 seed was similar at 14 and 63 days of AR (Table 2). The germination response of the 1998 and 1999 seed collected in the same locations (Hinds and Whiteoak) and seasonal times (JW 32 and 36) depended on location, JW, and AR duration (year*location*JW*duration p<.0001). In general, 1998 seed was more germinable than 1999 seed for three populations (Hinds JW32 and JW36, Whiteoak JW36) with AR durations of 35-36 and 45-49 days. Germination of 1998 and 1999 seed was similar for all four populations at 14-15 days of AR, and for the Whiteoak JW32 population at all AR durations (Table 2). 3.2. Germination Heterogeneity within Years In all three years, after-ripening stimulated seed germination (ANOVA p-values <.0001).Generally, longer AR durations had higher germination than shorter durations (tables 3-5), but the effect of AR was not consistent for all populations (duration*population interactions, p<.0001). 3.2.1. 1997 The least germinable 1997 population for most AR durations was Oakwood JW34 (O97-34) (Table 3).The most germinable populations for all AR durations were O97-36 and O97-37, which were similar to each other.Germination of the Curtiss JW36 population (C97-36) was intermediate to O97-34 and O97-36/O97-37. 3.2.2. 1998 Germination differed among 1998 populations at all AR durations (all p<.0001).The greatest range in germination occurred at 35 days AR when it varied from 9% for C98-32 to 93% for X98-39 (Table 4).Germination ranking among populations within a single AR duration changed between durations, though W98-32 was often among the least germinable populations and M98-40 was often among the most International Journal of Plant Research 2012, 2(3): 46-56 51 germinable. Seasonal time of abscission.Generally, in 1998, S. faberi seed collected early in the season was more dormant than seed collected in the middle of the season, which in turn was more dormant than seed collected late in the season. Differences in germination between these seasonal periods were significant (ANOVA contrasts) in most, but not all, cases (Table 6, top). The seed used for these contrasts was from the four locations (Curtiss, Hinds, Johnson, and Whiteoak) which had seed collected at a common time during all three periods (early, JW32; middle, JW36; late, JW 40). Table 2. Comparison of 1997—1998 seed germination (Percent, least square mean) (top) and 1998—1999 seed germination (bottom) with after-ripening for the Curtiss (C97, C98) populations collected in Julian week (JW) 36 and the Hinds (H98, H99) and Whiteoak (W98, W99) populations collected in JW32 and JW36. Germination percentages within the same after-ripening duration with the same letter were not significantly different (probability>.05) 1997—1998 Population C97-36 C98-36 1998—1999 14 17 A 12 A After-ripening duration (days) 35 49 62 A 62 B 44 B 78 A 63 62 A 73 A 77 58 B 78 A Population H98-32 H99-32 After-ripening duration (days) 14-15 35-36 1 C 41 B 0 C 9 C 45-49 90 A 21 D H98-36 H99-36 15 AB 22 A 85 A 48 B 90 A 51 B W98-32 W99-32 1 C 0 C 20 C 4 C 41 BC 35 BCD W98-36 W99-36 6 BC 6 BC 52 B 19 C 77 A 32 CD Table 3. Germination (percent seed germination, least square mean) of S. faberi seed populations collected in 1997 and evaluated in 1998 versus after-ripening duration. Populations: Curtiss farm (C97) and Oakwood drive (O97) populations collected during Julian weeks 34 (O97-34), 36 (C97-36; O97-36) and 37 (O97-37). Germination percentages within the same after-ripening duration with the same letter were not significantly different (probabil- ity>.05) Population C97-36 O97-34 O97-36 O97-37 14 17 B 10 B 40 A 53 A After-ripening duration (days) 35 49 62 A 62 B 33 B 30 C 74 A 90 A 75 A 77 A 63 62 A 27 B 82 A 70 A 77 58 B 39 B 82 A 81 A Table 4. Germination (1percent seed germination, least square mean (LSMean)) of S. faberi collected in 1998 with after-ripening (AR) duration (days). Populations (see table 1 for full description) grouped by inter-AR group (see Methods & Materials, Analysis): top, inter-AR group 1; middle, inter-AR group 2; bottom, inter-AR group 3. LSMeans within the same AR duration with the same letter were not significantly different (Tukey’s test, probability>.05) Population 14 Setariafaberi: Inter-AR Group 1 C98-40 36 AB X98-39 30 ABC H98-40 28 ABCD W98-40 20 BCDE M98-40 10 EF S. faberi: Inter-AR Group 2 H98-36 15 CDEF J98-40 1 F J98-36 11 DEF H98-32 1 F R98-34 0 F C98-36 12 DEF W98-36 6 EF X98-34 0 F S. faberi: Inter-AR Group 3 M98-34 0 F J98-32 0 F C98-32 0 F W98-32 1 F After-ripening duration (days)1 35 49 92 A 93 A 79 ABCD 80 ABCD 81 ABC 90 AB 97 A 93 AB 79 ABC 85 ABC 85 ABC 71 ABCDE 58 DEFG 41 GHI 69 BCDE 44 FGH 52 EFG 65 CDEF 90 AB 93 AB 91 AB 90 AB 82 ABC 78 ABC 77 ABC 67 C 29 HIJ 18 JK 9 JK 20 IJK 73 BC 75 BC 72 BC 41D 63 94 AB 92 ABC 85 ABCD 75 BCD 97 A 86 ABCD 86 ABCD 87 ABCD 83 ABCD 88 ABCD 73 CDE 81 ABCD 92 ABC 72 DE 82 ABCD 88 ABCD 48 F 77 93 AB 94 AB 84 ABC 80 ABC 97 A 86 ABC 87 ABC 87 ABC 90 ABC 88 ABC 78 ABC 71 C 95 AB 76 BC 88 ABC 87 ABC 41 D 52 K. Jovaag et al.: SetariaFaberi Seed Heteroblasty Blueprints Seedling Recruitment: I. Seed Dormancy Heterogeneity at Abscission Table 5. Germination (1percent seed germination, least square mean) of S. faberi collected in 1999 with after-ripening (AR) duration (days). Populations (see table 1 for full description) grouped by inter-AR group (see Methods & Materials, Analysis): top, inter-AR group 1; middle top, inter-AR group 2; middle bottom, inter-AR group 3; bottom, inter-AR group 4; bottom. Means within the same AR duration with the same letter were not significantly different (Tukey’s test, probability>.05) Part 1 (AR 6-24 d) Population 6 S. faberi: Inter-AR group 1 B99-40 13 CDE K99-40 19 BC H99-41 41 A J99-42 13 CD W99-42 28 AB S. faberi: Inter-AR group 2 B99-36 2 DE C99-38 7 CDE C99-42 13 CDE J99-38 2 DE S. faberi: Inter-AR group 3 H99-36 5 DE S. faberi: Inter-AR group 4 B99-32 0 E K99-36 0 E K99-32 0 E W99-36 0 E C99-35 0 E W99-32 0 E J99-35 H99-32 1 E 0 E After-ripening Duration (days)1 9 12 15 27 B 16 CDE 46 A 19 C 20 BCD 31 AB 17 BCDE 45 A 27 BC 29 ABC 47 A 26 B 52 A 24 B 24 B 0 H 10 EFG 11 DEF 2 FGH 3 EF 7 DEF 13 CDEF 4 EF 6 CD 11 BCD 25 B 3 D 10 EFG 22 BCD 22 BC 0 H 2 FGH 0 H 1 GH 0 H 0 H 0 H 0 H 2 EF 1 EF 0 F 1 EF 0 F 0 F 0 F 0 F 0 D 3 D 0 D 6 CD 0 D 0 D 0 D 0 D 18 21 24 46 A 41 AB 45 A 32 ABC 19 CDEF 55 A 47 AB 59 A 30 C 23 CD 66 A 57 A 53 AB 20 DE 35 BCD 7 DEFG 11 DEFG 23 BCD 1 FG 15 DEF 23 21 CDE 15 32 BC 22 3 F 0 CDE EF CDE F 20 CDE 35 BC 38 BC 2 EFG 5 DEFG 0 G 11 DEFG 1 FG 0 G 0 G 0 G 5 EF 8 EF 7 DEF 7 EF 1 F 2 F 5 EF 10 EF 5 EF 2 F 0 F 2 F 2 F 6 EF 2 F 5 EF Part 2 (AR 27-45 d) Population 27 After-ripening duration (days)1 30 33 36 S. faberi: Inter-AR group 1 B99-40 65 A 72 K99-40 61 AB 82 H99-41 53 AB 48 J99-42 24 DEFG 29 W99-42 27 DE 40 S. faberi: Inter-AR group 2 B99-36 34 CD 38 C99-38 23 DEFGH 25 C99-42 23 DEFGH 18 J99-38 5 IJ 4 S. faberi: Inter-AR group 3 H99-36 47 BC 64 S. faberi: Inter-AR group 4 B99-32 25 DEFG 19 K99-36 11 FGHIJ 16 K99-32 1 J 2 W99-36 11 FGHIJ 10 C99-35 15 EFGHIJ 7 W99-32 1 J 5 J99-35 10 GHIJ 10 H99-32 9 HIJ 7 A A BC CDEF CD 66 AB 76 A 51 BCD 28 EF 37 CDE CDE 50 BCD CDEFG 24 EFGH DEFGH14 FGHI GH 24 EFGH AB 56 ABC DEFGH30 DEFG EFGH 22 EFGH GH 13 FGHI FGH 16 EFGHI GH 14 FGHI GH 7 HI FGH 9 GHI GH 10 FGHI 70 AB 81 A 52 BCD 32 DEF 45 CDE 58 ABC 32 DEFG 25 EFGHI 28 DEFGH 48 BCDE 32 DEFG 26 EFGH 10 GHI 19 FGHI 16 FGHI 4 HI 15 FGHI 9 GHI 39 73 AB 77 A 42 CDEF 32 EFGH 45 CDE 54 BC 34 DEFGH 25 FGH 32 DEFGH 49 CD 39 CDEF 34 DEFGH 25 FGH 34 DEFGH 28 EFGH 19 GHI 19 GHI 16 HI 42 78 A 67 AB 49 BCDEF 32 EFGH 43 CDEFG 56 ABCD 42 CDEFG 18 HI 30 EFGH 59 ABC 34 DEFGH 52 BCDE 32 EFGH 25 GH 26 FGH 28 FGH 28 FGH 15 HI 45 65 AB 35 DEF 44 CDE 60 ABC 0 G 71 A 34 DEF 16 FG 30 EF 51 ABCD 45 BCDE 70 A 68 A 33 DEF 22 F 32 DEF 22 F 21 F 3.2.3. 1999 Germination differed among 1999 populations at all AR durations (all p<.0001).The greatest range in germination occurred at 30 days of AR where average germination ranged from 2% for K99-32 to 82% for K99-40 (table 5).Germination ranking among populations within a single AR duration changed between AR durations, though H99-32 was often among the least germinable populations and the SE Research Station (JW40) was often among the most germinable. Seasonal time of abscission. In 1999, the same 1998 sea- sonal pattern of increasing germinability was observed: S. faberi seed collected early in the season was more dormant than seed collected in the middle of the season, which in turn was more dormant than seed collected late in the season. Differences in germination between these seasonal periods were significant (ANOVA contrasts) in most, but not all, cases (table 6, bottom).The seed used for these contrasts was from the four locations (Hinds, SE Research sta- International Journal of Plant Research 2012, 2(3): 46-56 53 tion sites 1&2, and Whiteoak) which had seed collected at a common time during all three periods (early, JW32; middle, JW36; late, JW 40). Regional variation. Germination of the Crawfordsville populations was within the range of the Ames populations (Table 5) for shorter AR durations. With longer AR durations, the Crawfordsville populations, especially those from the latest seasonal collection dates (B99-40 and K99-40), were among the least dormant 1999 populations. 3.3. General Patterns in Germination Patterns in germination heterogeneity among populations were evaluated by ranking the populations into inter-AR groups.The clustering procedure used to obtain these inter-AR groups was effective.For the simulated data, it correctly classified 80% (simulated 1998 data) to 93% (simulated 1999 data) of the populations. population (H99-36), but its pattern was different from the other groups, and thus is presented separately (table 5). Mean germination for H99-36 started out lower than in groups 1 and 2, but had a greater rate of increase in germination in response to AR for the first 35 days of AR. The germination pattern for seasonal time of abscission (increasing germinability from early to late) was also observed in the 1998 and 1999 inter-AR groups, e.g., H9932/36/41. Populations collected late in the season tended to be in group 1 (the most germinable group for both years). Populations collected in the middle of the season tended to be in group 2 in 1998 and groups 2 or 3 in 1999.Populations collected early in the season tended to be in group 3 in 1998 or group 4 in 1999 (the least germinable groups).In all seasonal periods there were exceptions (Tables 4-5). 3.3.1. Patterns across AR Durations (Inter-AR Groups) Three basic germination patterns in response to increasing after-ripening were revealed by inter-AR grouping. The first pattern was a rapid increase in germinability at the shorter durations then remaining steadily high at longer durations, the second was a relatively consistent increase in germinability as duration increased, and the third was little or no early germination but a rapid increase with longer durations. 1998. Generally, the mean germination for 1998 inter-AR groups 1 and 2 show a rapid increase at the shorter durations, then steady, high germination at the longer durations (Figure 1, top right).The amount of germination was greater in group 1 than in group 2 at the shorter durations, then similar at the longer durations. Germination in group 3 increased at a relatively slower rate with increasing after-ripening duration compared to groups 1 and 2, and was also less germinable. 1999.Generally, mean germination for 1999 inter-AR groups 1 and 2 showed a relatively constant increase for the first 36 days of AR, then remained steady with increasing after-ripening duration (Figure 1, bottom right), but the amount of germination was higher in group 1 than in group 2 at all AR periods. Mean germination for the most dormant group (4), was very low at first, then began to increase with longer after-ripening durations. Group 3 contained only one Figure 1. Germination (percent seed germination, least square mean, smoothed curves) versus after-ripening (AR) duration (days) for all individual 1998 (top left) and 1999 populations (bottom left), and for the 1998 (top right) and 1999 (bottom right) inter-AR groups (See tables 4-5 for populations included in each inter-AR group). Individual populations with unusual patterns are shown as dashed lines; 1: W98-32, A: K99-40, B: B99-40, C: B99-36, D: H99-36, E: H99-41, F: W99-42. Line numbers in the group plots are the inter-AR group numbers. Group 3, 1999, is not shown in the bottom right plot as it consists of a single population—H99-36, line D, lower left Table 6. Difference in S. faberi germination (percent germination, least square mean) among populations collected during the early (Julian week (JW) 32), middle (JW36) and late (JW40) seasonal periods of the seed rain in 1998 and 1999 with after-ripening (1998: 14-77 days; 1999: 6-45 days). Populations used: 1998, Curtiss, Hinds, Johnson, and Whiteoak; 1999, Hinds, SE Research station sites 1&2, and Whiteoak. 1NS=no significant difference (ANOVA contrast, probability (p)>.05), *=.01

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