Contribution of Awns to Seed Yield and Seed Shattering in Siberian Wildrye Grown under Irrigated and Rainfed Environments

Fabrice Ntakirutimana; Yiyang Wan; Wenhui Liu; Wengang Xie

doi:10.3390/agronomy11112219

Ntakirutimana, Fabrice;Wan, Yiyang;Liu, Wenhui;Xie, Wengang

2021-11-02 00:00:00

agronomy Article Contribution of Awns to Seed Yield and Seed Shattering in Siberian Wildrye Grown under Irrigated and Rainfed Environments 1 , 2 , 3 1 4 1 , Fabrice Ntakirutimana , Yiyang Wan , Wenhui Liu and Wengang Xie * State Key Laboratory of Grassland Agro-Ecosystems, Key Laboratory of Grassland Livestock Industry Innovation, Ministry of Agriculture, College of Pastoral Agriculture Science and Technology, Lanzhou University, Lanzhou 730020, China; fabrice.ntakirutimana@ird.fr (F.N.); wanyy19@lzu.edu.cn (Y.W.) Université de Montpellier, Place Eugène Bataillon, 3400 Montpellier, France Institut de Recherche pour le Développement, UMR DIADE, 911 Avenue Agroprolis, 34394 Montpellier, France Key Laboratory of Superior Forage Germplasm in the Qinghai-Tibetan Plateau, Qinghai Academy of Animal Science and Veterinary Medicine, Xining 810008, China; qhliuwenhui@163.com * Correspondence: xiewg@lzu.edu.cn; Tel.: +86-931-891-3014 Abstract: The seed yield of grass species is greatly dependent on inﬂorescence morphological traits, starting with spikelets per inﬂorescence and seeds per spikelet, to kernel size, and then to awns. Previous studies have attempted to estimate the contribution of these traits on the harvested yield of major cereal crops, but little information can be accessed on the inﬂuence of awns on seed yield of forage grass species. Siberian wildrye (Elymus sibiricus L.) is a widely important perennial forage grass used to increase forage production in arid and semi-arid grasslands. The grass has long inﬂorescences with long awns developed at the tip end of the lemmas in the ﬂorets. In order to evaluate the effect of Citation: Ntakirutimana, F.; Wan, Y.; awns on Siberian wildrye seed production, awn excision analyses from 10 accessions were performed Liu, W.; Xie, W. Contribution of Awns at ﬂowering stage under irrigated and rainfed regimes. Overall, awn excision reduced thousand-seed to Seed Yield and Seed Shattering in weight and seed size under both irrigated and rainfed regimes, which decreased ﬁnal seed yield Siberian Wildrye Grown under per plant. De-awned plants produced signiﬁcantly more seeds per inﬂorescence, but spikelets per Irrigated and Rainfed Environments. inﬂorescence was not inﬂuenced by awn excision in either condition. Moreover, histological analyses Agronomy 2021, 11, 2219. https:// showed a high degradation of the abscission layer in the awned plants than de-awned ones, and doi.org/10.3390/agronomy11112219 awn excision evidently improved average seed breaking tensile strength (BTS), and thus decreased Academic Editor: Catherine the degree of seed shattering. In conclusion, the observed signiﬁcant impact of awn excision on Picon-Cochard different yield-related traits mirrored the impact of awns on the performance of Siberian wildrye under diverse growing conditions. These results provide useful information for plant breeders, seed Received: 19 September 2021 producers, and researchers to efﬁciently improve seed production in Siberian wildrye. Accepted: 29 October 2021 Published: 2 November 2021 Keywords: abscission layer; awns; Elymus sibiricus; grasses; inﬂorescence morphology; photosynthe- sis; seed shattering; seed yield; yield components Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional afﬁl- iations. 1. Introduction Siberian Wildrye (Elymus sibiricus L.) is a perennial, self-pollinating allotetraploid bunchgrass species that is important for arid and semi-arid regions [1]. Siberian wildrye has an erect culm ranging from 40 to 90 cm long, and the leaves are basal and cauline. Copyright: © 2021 by the authors. The inﬂorescence of Siberian wildrye is a nodding spike containing 15–30 spikelets, with Licensee MDPI, Basel, Switzerland. 4–5 fertile ﬂorets in each spikelet, and bristle, curling awns developed at the tip of the This article is an open access article lemmas in the ﬂorets, which can reach 20 mm in length. The grass is native to high- distributed under the terms and altitude regions of western and northern China, and widely distributed in Northern conditions of the Creative Commons Europe, Northern Asia, and North America [2]. The species plays an important role in Attribution (CC BY) license (https:// maintaining and developing the alpine pastures because of its seedling vigor and resistance creativecommons.org/licenses/by/ to pests and stress conditions. Owing to its forage yield potential and palatability (for 4.0/). Agronomy 2021, 11, 2219. https://doi.org/10.3390/agronomy11112219 https://www.mdpi.com/journal/agronomy Agronomy 2021, 11, 2219 2 of 16 livestock), it is favored by farmers, especially in the Qinghai–Tibet plateau of China, and some cultivars have been developed and distributed in the region [3]. Under natural conditions, however, Siberian wildrye is biologically inefﬁcient at producing seeds and thus cannot meet the growing seed demand for ecological restoration and research purposes. Seed yield ﬂuctuation in this species may be due to insufﬁcient assimilates for developing kernels, especially during the last growth stages [4,5]. Thus, it is critical to develop feasible approaches to improve seed yield of Siberian wildrye, especially under water deﬁcit and high-temperature conditions. Unlike cereal crops, most forage grass species are neglected for their capacity for seed production, and most breeding programs mainly focus on biomass yield, forage quality, and abiotic and biotic resistance [6]. Thus, the most feasible approach to improving seed yield of forage grass species is to focus on the traits that comprehensively inﬂuence seed yield under diverse growing conditions. Under stress-free conditions, the development and ﬁlling of kernels depend on the assimilates produced by leaves [7]. However, under unfavorable conditions (water limitation and high temperatures), the contribution of leaves to photosynthesis decreases sharply [8]. Thus, the focus should be whether the photosynthetic capacity of the inﬂorescence could support carbon assimilation during kernel development after premature leaf senescence. The photosynthetic capacity of grass inﬂorescence could contribute between 10% and 76% of ﬁnal seed weight, depending on the species and growing conditions, with awns playing a crucial role [9]. Awns, the bristle-like outgrowths of the lemmas in the ﬂorets, are morphological features of several cereal crops such as rice, wheat, and barley, as well as many forage grass species [10]. Awns could function at different plant development stages spanning from seed germination and ﬂoral development to grain setting and grain ﬁlling [11]. Awns inﬂuence seed dispersal and burial, and protect the kernel against animal predators [11,12]. The awn is triangular-shaped at its cross-section, with the base oriented towards the rachis and containing vascular bundles and chlorenchyma cells with the potential to improve the photosynthetic capacity of the canopy [13]. Awns are genetically controlled and are a highly heritable trait with the relatively high broad-sense heritability previously observed (H = 0.75) [14]. The connection between awns and yield-related traits such as grains per plant, grain size, and kernel weight has been reported in some cereal crops [15]. Awns could improve yield potential by improving the photosynthetic rate of the canopy, water-use efﬁciency, and thermo-tolerance [16]. In barley, long awns have resulted in the highest grain yield per plant under well-watered regimes [13]. Under water-stress conditions, however, long awns compete with growing kernels, thus reducing harvested grain yield [7]. In other cereals such as wheat, awn x environment interaction is unclear, with some studies reporting that awns could double the net photosynthetic rate of the canopy under favorable growing conditions. For example, Rebetzke et al. [8] observed that awns of wheat are coupled with increased grain size and yield under rainfed conditions, but they considerably decreased grain number under irrigated conditions, which could result in reduced grain yield. Blum [17] reported that awns of wheat contributed to about 50% of the total canopy carbon exchange rate under well-watered regimes. Similarly, Maydup et al. [18] observed that 45% of the yield increased in awned wheat cultivars under water- limited environments. In comparison, the contribution of awns to grain yield of rice varied depending on production systems. In paddy rice genotypes, awns are considered a less important trait for yield potential as several studies observed no signiﬁcant differences between awned and awnless genotypes [19,20]. In some upland rice landraces, such as Tipakhiya and Sathi, the removal of awns accelerated water loss in the panicle, which resulted in grain sterility [21]. Seed shattering is an essential trait for the efﬁcient propagation of offspring in nature, yet this may threaten row crop production by increasing yield loss in cultivated species [22]. Thus, a reduction in seed shattering will increase seed yield in grain crops. In monocots, seed shattering is generally induced by the progressive degradation of the abscission layers developed at the attachment point between the lemma and the pedicel [23]. Very few Agronomy 2021, 11, 2219 3 of 16 studies have demonstrated the association of seed shattering and ﬂoral morphological structures. A previous study on Siberian wildrye mentioned that seed shattering is induced by seed traits such as kernel weight, seed length, and awns [22]. Another study on wheat indicated that long awns are easily controlled by external dispersal factors such as wind, and their movement may propel the seed into the ground [12,19]. Compared to major cereal crops, very few studies have investigated the impact of awns on seed production of forage grasses. In addition, the association between awns and seed shattering in Siberian wildrye remains unknown. The aim of this study was to assess the impact of awn removal on seed yield, yield components, and seed shattering of Siberian wildrye under irrigated and rainfed regimes. The results of this study will enable Siberian wildrye seed producers, plant breeders, and seed production researchers alike to more effectively understand traits coupled with seed yields. 2. Materials and Methods 2.1. Plant Materials The contribution of awns to seed yield, seed shattering, and other seed yield-related traits was analyzed in a total of 10 Siberian wildrye accessions (Table 1). These accessions were selected by evaluating awn length and were screened from 80 Siberian wildrye accessions. In this species, long-awned genotypes usually have awn lengths of about 20 mm, while short-awned genotypes have awns of less than 10 mm in length [4]. To ensure phenotypic variation, both long-awned and short-awned accessions were selected. The seeds of these accessions were obtained from the U.S. Department of Agriculture Germplasm Resources Information Network (GRIN), Sichuan Agricultural University, Sichuan Academy of Grassland Science, and Lanzhou University. Before planting, the seeds were germinated in plastic boxes containing a moistened double layer of blotter paper at 25 C, 85% relative humidity, and a photoperiod of 12 h light, 12 h dark. Seedlings were grown under greenhouse conditions until they reached 8 weeks. Table 1. Siberian Wildrye accessions used in the study. Running Code Accessions Status Origin 1 PI499456 Wild Inner Mongolia, China 2 LT02 Wild Gansu, China 3 PI499615 Wild Xinjiang, China 4 PI531665 Wild Beijing, China 5 ZN03 Wild Gansu, China 6 PI598479 Wild Altai, Russia 7 PI598788 Wild Alma Ata, Kazakhstan 8 PI655097 Wild Alma Ata, Kazakhstan 9 PI659942 Wild Alma Ata, Kazakhstan 10 HZ03 Wild Gansu, China 2.2. Experimental Conditions and Trial Design The ﬁeld trial was carried out at the Yuzhong experimental station of Lanzhou Uni- 0 0 versity in Gansu province, China (latitude: 35 34 N, longitude: 103 34 E, elevation: 1720 m). The soil at the site was sandy loam (organic matter content 2.4%, pH 7.6) with a depth of about 0.82 m and a dry bulk density of about 1.42 gcm . The 10 accessions were grown under irrigated and rainfed conditions during two successive growing seasons (2018 and 2019), which denoted as Season 1 and Season 2, respectively. Weather data were collected from Yuzhong meteorological station located at ~2 km from the experimental site (CMA Archives, 2019). The location received an average monthly rainfall of ~9.15 mm and ~31.57 mm in 2018 and 2019, respectively (Figure 1). The maximum temperatures in sum- mer ranged from 22–26 C in 2018 and from 22–29 C in 2019. The minimum temperatures in winter ranged from8 to5 C in 2018 and6 to2 C in 2019. In Season 1, compared to Season 2, the rainfall was much less during the vegetative growth stage, which is the Agronomy 2021, 11, x FOR PEER REVIEW 4 of 16 Archives, 2019). The location received an average monthly rainfall of ~9.15 mm and ~31.57 mm in 2018 and 2019, respectively (Figure 1). The maximum temperatures in summer ranged from 22–26 °C in 2018 and from 22–29 °C in 2019. The minimum temperatures in winter ranged from −8 to −5 °C in 2018 and −6 to −2 °C in 2019. In Season 1, compared to Season 2, the rainfall was much less during the vegetative growth stage, which is the growth between early seedling emergence and the anthesis (May, June, July), than seed development stages. Moreover, the average temperature of both seasons increased during anthesis and seed development stages, and this increment was more pronounced in the second season than the first. The plots were arranged in a randomized complete block design with three repli- cates. Individual treatment plots were 30 m (6 m long × 5 m wide; 50 cm row spacing and 20 cm inter-plant spacing), and seedlings were transplanted at an optimal 10–15 cm depth. Agronomy 2021, 11, 2219 4 of 16 After transplanting, a total of 50 mm of water was applied immediately in both irrigated and rainfed plots and no fertilizers were applied afterwards. A total of 75 mm was addi- tionally added to the irrigated plots between heading to maturity. When plants reached growth between early seedling emergence and the anthesis (May, June, July), than seed anthesis stage, two treatments involving the presence (awned) and absence (de-awned) of development stages. Moreover, the average temperature of both seasons increased during awns were imposed. Within each plot, treatment was replicated three times. Excision of anthesis and seed development stages, and this increment was more pronounced in the awns was performed for basal, central, and apical spikelets with scissors. second season than the ﬁrst. Figure 1. Maximum and minimum temperatures and precipitation at the Yuzhong experimental Figure 1. Maximum and minimum temperatures and precipitation at the Yuzhong experimental station (Lanzhou, Gansu, China) from January 2018 to December 2019. station (Lanzhou, Gansu, China) from January 2018 to December 2019. The plots were arranged in a randomized complete block design with three replicates. 2 Individual .3. Data C trolle eatmen ction t plots and M wer ea es30 ure m me(6 nts m long 5 m wide; 50 cm row spacing and 20 cm inter-plant spacing), and seedlings were transplanted at an optimal 10–15 cm depth. After 2.3.1. Awn Length and Seed Yield Components transplanting, a total of 50 mm of water was applied immediately in both irrigated and Seed-related traits were measured at early maturity stage (21 days after anthesis). rainfed plots and no fertilizers were applied afterwards. A total of 75 mm was additionally added to the irrigated plots between heading to maturity. When plants reached anthesis Seed samples were oven-dried at 80 °C for 2 days, and clean and dry seed samples were stage, two treatments involving the presence (awned) and absence (de-awned) of awns stored in paper bags at 20 °C and 15% relative humidity before being subjected to meas- were imposed. Within each plot, treatment was replicated three times. Excision of awns urements. For awn length (AL), seed length (SL), and seed width (SW), seeds sampled in was performed for basal, central, and apical spikelets with scissors. the basal, central, and apical spikelets were used; fifty random seeds were chosen in each sa 2.3. mData ple. Collection Seeds were and Measur scanne ements d by Epson Perfection V700 Scanner (Seiko Epson Corp., Na- 2.3.1. Awn Length and Seed Yield Components gano, Japan). The images were analyzed by Image J software [24]. Thirty random inflores- Seed-related traits were measured at early maturity stage (21 days after anthesis). Seed cences were used to evaluate spikelets per inflorescence (SpI), seeds per inflorescence (SI), samples were oven-dried at 80 C for 2 days, and clean and dry seed samples were stored florets per spikelet (FS), and seeds per spikelets (SSp). All these measurements were meas- in paper bags at 20 C and 15% relative humidity before being subjected to measurements. ured from the same spikelets. To obtain thousand-seed weight (TSW), thirty random in- For awn length (AL), seed length (SL), and seed width (SW), seeds sampled in the basal, florescences from each plant were selected. The TSW was determined by averaging the central, and apical spikelets were used; ﬁfty random seeds were chosen in each sample. weight of three thousand seed samples from basal, central, and apical spikelets. Seeds were scanned by Epson Perfection V700 Scanner (Seiko Epson Corp., Nagano, Japan). The images were analyzed by Image J software [24]. Thirty random inﬂorescences were used to evaluate spikelets per inﬂorescence (SpI), seeds per inﬂorescence (SI), ﬂorets per spikelet (FS), and seeds per spikelets (SSp). All these measurements were measured from the same spikelets. To obtain thousand-seed weight (TSW), thirty random inﬂorescences from each plant were selected. The TSW was determined by averaging the weight of three thousand seed samples from basal, central, and apical spikelets. 2.3.2. Spike Dry Matter Spike dry matter (SDM) was estimated at early maturity stage (21 days after anthesis). Ten random tillers of each plant in each treatment were selected, and their spikes were careful hand-cut just below the spike and oven-dried at 80 C for 2 days [5]. Before Agronomy 2021, 11, 2219 5 of 16 measurement, awns were also removed for awned spikes to avoid differences that could be caused by the presence of awns. The dried spikes were weighed, and data were expressed as g tiller-1. 2.3.3. Seed Yield In early August of each year (2018 and 2019) when seeds had fully matured (28 days after anthesis), a total of 10 plants of each treatment were randomly selected, and the heads of each plant were carefully hand-cut. To avoid border effects, seed samples were taken from the center of each plot. Seed samples were harvested when the seed moisture content was approximately 45%. Seed yield per plant (SYP) measurement was carried out after samples were weighed and when the seed moisture content was about 10%. 2.3.4. Seed Shattering Breaking Tensile Strength (BTS) Seed shattering was determined by measuring the minimum breaking tensile strength (BTS) required to detach seeds from pedicels. The spikes were carefully harvested at early maturity (21 days after anthesis). Each spike was attached vertically upside down to a digital force gauge (HANDIPI, China), and forceps were used to pull down each seed. The BTS measured was recorded in gram-force (gf) units. A total of 50 seeds from ﬁve spikes representing each plant in each treatment were measured. Scanning Electron Microscope (SEM) For histological analysis, abscission zone tissues of the two accessions (TZ02 and ZN03) with contrasting awn length and degree of seed shattering were used. Samples were collected from three central spikelets from each inﬂorescence at early maturity stage (28 days after heading). The samples were ﬁxed in FAA solution [ethylalcohol (70%):glacial acetic acid:formaldehyde (40%) = 90:5:5)] at 4 C. Transverse sections were achieved by hand-cutting through the seed and pedicel junction. The sections were dehydrated in a series of ethanol solutions (50, 70, 90, and 100%), substituted in 3-methylbutyl acetate, and vacuum dried. Sections were then gold plated and observed using a Hitachi S-3000N variable pressure scanning electron microscope. 2.4. Statistical Analysis The statistical analyses were performed using R statistical software (version 4.0.1; R Foundation for Statistical Computing, Vienna, Austria). The data were ﬁrst checked for normality and error variance heterogeneity. The normality tests showed non-signiﬁcant error variances (data not shown), and the data were left untransformed. The data of seed yield per plant, yield components, and seed shattering were subjected to analysis of variance (ANOVA). The presence (awned) and absence (de-awned) of awns and growing conditions (irrigated and rainfed) were treated as ﬁxed factors, while block and season were treated as random factors. Means were compared by using the Student’s t-test and Turkey’s HSD post hoc test with a level of signiﬁcance of p < 0.05. To ensure reproducibility, all the experiments were replicated at least three times. 3. Results 3.1. Awn Length and Seed Yield Components The ANOVA showed that the AL and seed yield components of 10 Siberian wildrye accessions differed in response to awn excision, environment, and their interaction (Table 2). The SL, SW, TSW, and SI were signiﬁcantly inﬂuenced by awn excision. All yield compo- nents, except BTS and SP, were signiﬁcantly affected by the environment. Across irrigated and rainfed conditions, six out of ten accessions, PI531665, ZN03, PI598479, PI598788, PI655097, and PI659942, had an AL longer than 10 mm (Figure 2). ZN03 showed the longest awns (18.64 mm) and TZO2 showed the shortest awns (8.05 mm). The average SL was signiﬁcantly inﬂuenced by awn excision under irrigated (awned, 9.50 mm; de-awned, Agronomy 2021, 11, x FOR PEER REVIEW 6 of 16 2). The SL, SW, TSW, and SI were significantly influenced by awn excision. All yield com- ponents, except BTS and SP, were significantly affected by the environment. Across irri- gated and rainfed conditions, six out of ten accessions, PI531665, ZN03, PI598479, PI598788, PI655097, and PI659942, had an AL longer than 10 mm (Figure 2). ZN03 showed the longest awns (18.64 mm) and TZO2 showed the shortest awns (8.05 mm). The average SL was significantly influenced by awn excision under irrigated (awned, 9.50 mm; de- awned, 9.23 mm; p < 0.05) and rainfed (awned, 9.36mm; de-awned, 9.04mm; p < 0.01) con- ditions (Figure 3). The average SW was also decreased by awn excision under irrigated (awned, 2.06 mm; de-awned, 1.89 mm; p < 0.001) and rainfed (awned, 1.90 mm; de-awned, Agronomy 2021, 11, 2219 6 of 16 1.75 mm; p < 0.001) conditions. Across both environments, the SpI was not significantly affected by awn excision (p > 0.05). However, awn excision strongly increased the average 9.23 mm; p < 0.05) and rainfed (awned, 9.36mm; de-awned, 9.04mm; p < 0.01) conditions SI under both irrigated (awned, 76.70; de-awned, 85.17; p < 0.01) and rainfed (awned, (Figure 3). The average SW was also decreased by awn excision under irrigated (awned, 72.73; de-awned, 82.81; p < 0.001) regimes. 2.06 mm; de-awned, 1.89 mm; p < 0.001) and rainfed (awned, 1.90 mm; de-awned, 1.75 mm; p < 0.001) conditions. Across both environments, the SpI was not signiﬁcantly affected Table 2. Analysis of variance for awns (A), environments (E), seasons (S), and interaction effects on by awn excision (p > 0.05). However, awn excision strongly increased the average SI seed yield and yield components. SL, seed length; SW, seed width; TSW, thousand-seed weight; under both irrigated (awned, 76.70; de-awned, 85.17; p < 0.01) and rainfed (awned, 72.73; BTS, breaking tensilede-awned, strength;82.81; SpI, p spi < k 0.001) elets rper egimes. inflorescence; SI, seeds per inflorescence; SDM, spike dry matter; SYP, seed yield per plant. ns: not significant. *, **, and ***: significant at 0.05, 0.01, Table 2. Analysis of variance for awns (A), environments (E), seasons (S), and interaction effects on seed yield and yield and 0.001 probability level. components. SL, seed length; SW, seed width; TSW, thousand-seed weight; BTS, breaking tensile strength; SpI, spikelets per inﬂorescence; SI, seeds per inﬂorescence; SDM, spike dry matter; SYP, seed yield per plant. ns: not signiﬁcant. *, **, and ***: Source of Variation df SL SW TKW BTS SpI SI SDM SYP signiﬁcant at 0.05, 0.01, and 0.001 probability level. Seasons (S) 1 ns ns ** ns *** ** ** ns Source of Blocks 2 ns ns ns ns ns ns ns ns df SL SW TKW BTS SpI SI SDM SYP Variation Awn (A) 1 *** *** *** *** ns *** ** ns Seasons (S) 1 ns ns ** ns *** ** ** ns Blocks Environme2 nt (E) ns 1 ns * *** ns *ns ns ns ns ns * ns* * ns Awn (A) 1 *** *** *** *** ns *** ** ns S X A 1 ns ns ns ns ns * * ns Environment (E) 1 * *** * ns ns * * * S x A 1 ns ns ns ns ns * * ns S X E 1 ns ns ns ns ns ns * ns S x E 1 ns ns ns ns ns ns * ns A X E 1 ns ns ns ns ns * * * A x E 1 ns ns ns ns ns * * * A x E x S 1 ns ns ns ns ns ns ns ns A X E X S 1 ns ns ns ns ns ns ns ns Figure 2. Characterization of Siberian wildrye accessions used in the study. (a) Awn length of 10 accessions used in the Figure 2. Characterization of Siberian wildrye accessions used in the study. (a) Awn length of 10 study. (b) Seeds of ZN03 and TZ02 accessions. b1 and b2 are awned and de-awned seeds of ZN03 under rainfed and accessions used in the study. (b) Seeds of ZN03 and TZ02 accessions. b1 and b2 are awned and de- irrigated conditions, respectively. b3 and b4 are awned and de-awned seeds of LT02 grown under rainfed and irrigated awned seeds of ZN03 under rainfed and irrigated conditions, respectively. b3 and b4 are awned and conditions, respectively. Each bar represents the mean value standard deviation. de-awned seeds of LT02 grown under rainfed and irrigated conditions, respectively. Each bar rep- Across both environments, the impact of awn excision on SL was non-signiﬁcant resents the mean value ± standard deviation. (p > 0.05) at apical, central, and basal spikelet positions (Figure 4). Under irrigated con- ditions, the average SW for all 10 accessions was signiﬁcantly reduced by awn excision at apical (awned, 2.07; de-awned, 1.88; p < 0.01), central (awned, 2.07; de-awned, 1.94; p < 0.01), and basal (awned, 2.03; de-awned, 1.86; p < 0.01) spikelet positions. Under the rainfed regime, the average SW was also inﬂuenced by awn excision at apical (awned, 1.93; de-awned, 1.78; p < 0.05) and basal (awned, 1.83; de-awned, 1.71; p < 0.05) spikelet positions. Although no signiﬁcant difference was observed for the average FS among awned and Agronomy 2021, 11, 2219 7 of 16 de-awned plants in both regimes, a slight but signiﬁcant increase in FS was observed for central spikelets under awn excision treatments in irrigated conditions (awned, 5.83; de-awned, 6.09; p < 0.05) and rainfed conditions (awned, 5.78; de-awned, 6.07; p < 0.05). Moreover, awn excision showed a signiﬁcant effect on SI at the apical (awned, 3.48; de- awned, 4.33; p < 0.01) and central (awned, 3.69; de-awned, 4.36; p < 0.05) spikelets under Agronomy 2021, 11, x FOR PEER REVIEW 7 of 16 irrigated conditions (Figure 5). Under both conditions, the TSW was not signiﬁcantly impacted by awn excision at all three spikelet positions (p > 0.05). Figure 3. Box plots of seed length (a), seed width (b), spikelets per inﬂorescence (c), and seeds per inﬂorescence (d), and Figure 3. Box plots of seed length (a), seed width (b), spikelets per inflorescence (c), and seeds per inflorescence (d), and signiﬁcance levels of difference between control and awn excision. ns: not signiﬁcant, * p <0.05, ** p <0.01, *** p <0.001. Each significance levels of difference between control and awn excision. ns: not significant, * p <0.05, ** p <0.01, *** p <0.001. Each box plot denotes the average of 10 accessions for corresponding traits. The signiﬁcances indicate the comprehensive effect box plot denotes the average of 10 accessions for corresponding traits. The significances indicate the comprehensive effect of awn excision on different traits of 10 Siberian wildrye accessions. of awn excision on different traits of 10 Siberian wildrye accessions. Measurements across both growing conditions revealed that awn excision varyingly Across both environments, the impact of awn excision on SL was non-significant (p inﬂuenced seed yield components of 10 Siberian wildrye accessions (Figure 6). For instance, > 0.05) at apical, central, and basal spikelet positions (Figure 4). Under irrigated condi- awn excision reduced the SL of all 10 accessions and this reduction was, on average, more pronounced in PI598479 (awned, 9.84 mm; de-awned, 9.31 mm; p < 0.001). Awn excision tions, the average SW for all 10 accessions was significantly reduced by awn excision at signiﬁcantly and consistently reduced the SW of seven accessions and this reduction was apical (awned, 2.07; de-awned, 1.88; p < 0.01), central (awned, 2.07; de-awned, 1.94; p < much higher in PI499456 (awned, 2.17 mm; de-awned, 1.95 mm; p < 0.001). The SI of 0.01), and basal (awned, 2.03; de-awned, 1.86; p < 0.01) spikelet positions. Under the rain- ﬁve accessions (PI499456, LT02, PI598788, PI655097, HZ03) was signiﬁcantly increased by fed regime, the average SW was also influenced by awn excision at apical (awned, 1.93; awn excision. The SI was, on average, higher in PI655097 (awned, 81.02; de-awned, 92.59; de-awned, 1.78; p < 0.05) and basal (awned, 1.83; de-awned, 1.71; p < 0.05) spikelet posi- p < 0.001) and HZ03 (awned, 80.48; de-awned, 91.27; p < 0.001). Moreover, the contribution tions. Although no significant difference was observed for the average FS among awned of awn excision for SpI, although different in some accessions, was non-signiﬁcant. and de-awned plants in both regimes, a slight but significant increase in FS was observed for central spikelets under awn excision treatments in irrigated conditions (awned, 5.83; de-awned, 6.09; p < 0.05) and rainfed conditions (awned, 5.78; de-awned, 6.07; p < 0.05). Moreover, awn excision showed a significant effect on SI at the apical (awned, 3.48; de- awned, 4.33; p < 0.01) and central (awned, 3.69; de-awned, 4.36; p < 0.05) spikelets under irrigated conditions (Figure 5). Under both conditions, the TSW was not significantly im- pacted by awn excision at all three spikelet positions (p > 0.05). Agronomy 2021, 11, 2219 8 of 16 Agronomy 2021, 11, x FOR PEER REVIEW 8 of 16 Agronomy 2021, 11, x FOR PEER REVIEW 8 of 16 Figure 4. Box plots summarizing seed length (a), seed width (b), and ﬂorets per inﬂorescence (c) in the apical, central, and Figure 4. Box plots summarizing seed length (a), seed width (b), and florets per inflorescence (c) in Figure 4. Box plots summarizing seed length (a), seed width (b), and florets per inflorescence (c) in basal spikelets of the spikes. ns: not signiﬁcant, * p < 0.05, ** p < 0.01. Each box plot denotes the average of 10 accessions for the apical, central, and basal spikelets of the spikes. ns: not significant, * p < 0.05, ** p < 0.01. Each the apical, central, and basal spikelets of the spikes. ns: not significant, * p < 0.05, ** p < 0.01. Each corresponding traits. The signiﬁcances indicate the comprehensive effect of awn excision on different traits of 10 Siberian box plot denotes the average of 10 accessions for corresponding traits. The significances indicate the box plot denotes the average of 10 accessions for corresponding traits. The significances indicate the comprehensive effect of awn excision on different traits of 10 Siberian wildrye accessions. wildrye accessions. comprehensive effect of awn excision on different traits of 10 Siberian wildrye accessions. Figure 5. Box plots summarizing seeds per spikelet (a), thousand-seed weight (b), and breaking Figure 5. Box plots summarizing seeds per spikelet (a), thousand-seed weight (b), and breaking Figure 5. Box plots summarizing seeds per spikelet (a), thousand-seed weight (b), and breaking tensile strength (c) in the tensile strength (c) in the apical, central, and basal spikelets of the spikes. ns: not significant, * p < tensile strength (c) in the apical, central, and basal spikelets of the spikes. ns: not significant, * p < apical, central, and basal spikelets of the spikes. ns: not signiﬁcant, * p < 0.05, ** p < 0.01, *** p < 0.001. Each box plot denotes 0.05, ** p < 0.01, *** p < 0.001. Each box plot denotes the average of 10 accessions for corresponding 0.05, ** p < 0.01, *** p < 0.001. Each box plot denotes the average of 10 accessions for corresponding the average of 10 accessions for corresponding traits. The signiﬁcances indicate the comprehensive effect of awn excision on traits. The significances indicate the comprehensive effect of awn excision on different traits of 10 traits. The significances indicate the comprehensive effect of awn excision on different traits of 10 different traits of 10 Siberian wildrye accessions. Siberian wildrye accessions. Siberian wildrye accessions. Agronomy 2021, 11, x FOR PEER REVIEW 9 of 16 Measurements across both growing conditions revealed that awn excision varyingly influenced seed yield components of 10 Siberian wildrye accessions (Figure 6). For in- stance, awn excision reduced the SL of all 10 accessions and this reduction was, on aver- age, more pronounced in PI598479 (awned, 9.84 mm; de-awned, 9.31 mm; p < 0.001). Awn excision significantly and consistently reduced the SW of seven accessions and this reduc- tion was much higher in PI499456 (awned, 2.17 mm; de-awned, 1.95 mm; p < 0.001). The SI of five accessions (PI499456, LT02, PI598788, PI655097, HZ03) was significantly in- creased by awn excision. The SI was, on average, higher in PI655097 (awned, 81.02; de- awned, 92.59; p < 0.001) and HZ03 (awned, 80.48; de-awned, 91.27; p < 0.001). Moreover, Agronomy 2021, 11, 2219 9 of 16 the contribution of awn excision for SpI, although different in some accessions, was non- significant. Figure 6. Seed length (a), seed width (b), spikelets per inﬂorescence (c), and seeds per inﬂorescence (d) of 10 Siberian Figure 6. Seed length (a), seed width (b), spikelets per inflorescence (c), and seeds per inflorescence wildrye accessions (1–10) and averages of accessions (11) under control and awn excision treatments across rainfed and (d) of 10 Siberian wildrye accessions (1–10) and averages of accessions (11) under control and awn irrigated conditions. Error bars represent mean standard deviation. ns: not signiﬁcant, * p < 0.05, ** p < 0.01, *** p < 0.001. excision treatments across rainfed and irrigated conditions. Error bars represent mean ± standard deviation. ns: not sign3.2. ifica Spike nt, * Dry p <Matter 0.05, ** Accumulation p < 0.01, *** p < 0.001. The SDM was signiﬁcantly inﬂuenced by awn excision, the environment, and their interaction (Table 2). The average SDM of awned plants was higher than that of de-awned 3.2. Spike Dry Matter Accumulation ones and was signiﬁcant in rainfed conditions (awned, 30.39 g; de-awned, 29.45 g; p < 0.05) The SDM was significantly influenced by awn excision, the environment, and their (Figure 7). Moreover, awn excision reduced the average SDM of 10 accessions, with signiﬁcant differences observed in LT02 (awned, 30.40 g; de-awned, 28.70 g; p < 0.05) and interaction (Table 2). The average SDM of awned plants was higher than that of de-awned PI499615 (awned, 30.70 g; de-awned, 28.88 g; p < 0.05) (Figure 8). ones and was significant in rainfed conditions (awned, 30.39 g; de-awned, 29.45 g; p < 0.05) (Figure 7). Moreover, awn excision reduced the average SDM of 10 accessions, with sig- nificant differences observed in LT02 (awned, 30.40 g; de-awned, 28.70 g; p < 0.05) and PI499615 (awned, 30.70 g; de-awned, 28.88 g; p < 0.05) (Figure 8). Agronomy 2021, 11, 2219 10 of 16 Agronomy 2021, 11, x FOR PEER REVIEW 10 of 16 Agronomy 2021, 11, x FOR PEER REVIEW 10 of 16 Figure Figure 7. 7. Box Box plots plots of of thousand-seed thousand-seed weight weight ((a a), ), spike spike dry dry matter matter ((b b), ), br breaking eaking tensile tensile str strength ength ((c c), ), Figure 7. Box plo and ts yo ie f ld th o per usa pl nd an -se t ( ed d) ,w aei nd gh si tg (n a) ifi , spi can k ce e dr lev yel m s ao tf ter di ( ffer b), en brc ea e k bin etg w t een ensi clo e nst trro el na gn th d (a cw ), n excision. ns: and yield per plant (d), and signiﬁcance levels of difference between control and awn excision. ns: and yield per plant (d), and significance levels of difference between control and awn excision. ns: not significant, * p < 0.05, ** p < 0.01, *** p < 0.001. Each box plot denotes the average of 10 accessions not signiﬁcant, * p < 0.05, ** p < 0.01, *** p < 0.001. Each box plot denotes the average of 10 accessions not significant,fo * rp c < o r 0r.es 05po , ** n p di< n 0 g. 0 tr 1a , it ** s. * Th p <e 0si .0g 0n 1ifi . Ea cacn hc b es o x in plot dica de te t n h o e tes co m thpr e a eh ver en asi ge ve ofeffect 10 ac o ces f asi w on n s ex cision on dif- for corresponding traits. The signiﬁcances indicate the comprehensive effect of awn excision on for corresponding traits. The significances indicate the comprehensive effect of awn excision on dif- ferent traits of 10 Siberian wildrye accessions. different traits of 10 Siberian wildrye accessions. ferent traits of 10 Siberian wildrye accessions. Figure 8. Thousand-seed weight (a), spike dry matter (b), breaking tensile strength (c), and seed Figure 8. Thousand-seed weight (a), spike dry matter (b), breaking tensile strength (c), and seed Figure 8. Thousand-seed weight yield per (a), pl spike ant (dry d) omatter f 10 Sib (er b), iabr n eaking wildrye tensile accessi str on ength s (1-10 (c ) ), an and d av seed eragyield es of a per cces plant sions (d (1 )1of ) under yield per planc t o (n dt )r o ol f a 1n 0 d S ib aw er n ia ex n c w is il io dr ny te rea actc m es en sit os na s c(1 ro-ss 10 ) ra ain nd fed av a en ra d gie rs rio gf ata ed cc es co si no di nt s io (1 n1 s. ) Er und roer r b ars represent 10 Siberian wildrye accessions (1–10) and averages of accessions (11) under control and awn excision treatments across control and awn excision treatments across rainfed and irrigated conditions. Error bars represent mean ± standard deviation. ns: not significant, * p < 0.05, ** p < 0.01, *** p < 0.001. rainfed and irrigated conditions. Error bars represent mean standard deviation. ns: not signiﬁcant, * p < 0.05, ** p < 0.01, mean ± standard deviation. ns: not significant, * p < 0.05, ** p < 0.01, *** p < 0.001. *** p < 0.001. 3.3. Seed Yield 3.3. Seed Yield The ANOVA showed that SYP was not significantly impacted by awn excision but The ANOVA showed that SYP was not significantly impacted by awn excision but was significantly influenced by the environment and the interaction between awn excision was significantly influenced by the environment and the interaction between awn excision Agronomy 2021, 11, 2219 11 of 16 Agronomy 2021, 11, x FOR PEER REVIEW 11 of 16 3.3. Seed Yield The ANOVA showed that SYP was not signiﬁcantly impacted by awn excision but awas nd th signiﬁcantly e environminﬂuenced ent (Table by 2). the The envir influence onment ofand awn the exinteraction cision on th between e average awn SY excision P was m and ore the pron envir ounce onment d in th(T e able rainfed 2). re The gim inﬂuence e (awnedof , 7.awn 32; dexcision e-awned,on 7.0 the 2; paverage < 0.05) th SYP an t was he irr mor igae ted pr onounced one (awned in, the 6.98rainfed g; de-ar wn egime ed, 7 (awned, .40 g; p > 7.32; 0.05 de-awned, ) (Figure 7) 7.02; . Assp essm < 0.05) ents than acrothe ss birrigated oth enviro one nm (awned, ents rev6.98 ealed g; a de-awned, wn excisio 7.40 n ing; fluence p > 0.05) d th (Figur e SYP e o 7f ). 1Assessments 0 accessions, acr alth oss ough both environments revealed awn excision inﬂuenced the SYP of 10 accessions, although this this was non-significant (Figure 8). The highest average SYP was found for PI499456 was non-signiﬁcant (Figure 8). The highest average SYP was found for PI499456 (awned, (awned, 6.98 g; de-awned, 7.40 g; p > 0.05), while the lowest value was found for ZN03 6.98 g; de-awned, 7.40 g; p > 0.05), while the lowest value was found for ZN03 (awned, (awned, 6.20 g; de-awned, 6.92 g; p > 0.05). 6.20 g; de-awned, 6.92 g; p > 0.05). 3.4. Effect of Awn Excision on Seed Shattering 3.4. Effect of Awn Excision on Seed Shattering There was a significant effect of awn excision on seed shattering (SS) in both growing There was a signiﬁcant effect of awn excision on seed shattering (SS) in both growing conditions (Table 2). Awn excision significantly reduced the degree of seed shattering by conditions (Table 2). Awn excision signiﬁcantly reduced the degree of seed shattering increasing the average BTS under both irrigated (awned, 59.46 gf; de-awned, 64.37 gf; p < by increasing the average BTS under both irrigated (awned, 59.46 gf; de-awned, 64.37 gf; 0.001) and rainfed conditions (awned, 61.09 gf; de-awned, 64.75 gf; p > 0.01) (Figure 7). p < 0.001) and rainfed conditions (awned, 61.09 gf; de-awned, 64.75 gf; p > 0.01) (Figure 7). Under irrigated conditions, measurements at three spikelet positions confirmed the major Under irrigated conditions, measurements at three spikelet positions conﬁrmed the major impact of awn excision on the average BTS at apical (awned, 58.91 gf; de-awned, 62.85 gf; impact of awn excision on the average BTS at apical (awned, 58.91 gf; de-awned, 62.85 gf; p < 0.05), central (awned, 58.19 gf; de-awned, 65.94 gf; p < 0.001), and basal (awned, 61.27 p < 0.05), central (awned, 58.19 gf; de-awned, 65.94 gf; p < 0.001), and basal (awned, gf; de-awned, 64.33 gf; p < 0.05) positions (Figure 5). Under rainfed conditions, awn exci- 61.27 gf; de-awned, 64.33 gf; p < 0.05) positions (Figure 5). Under rainfed conditions, awn sion significantly improved the average BTS of Siberian wildrye accessions at central excision signiﬁcantly improved the average BTS of Siberian wildrye accessions at central (awned, 60.93 gf; de-awned, 66.67 gf; p < 0.01) and basal (awned, 60.45 gf; de-awned, 64.31 (awned, 60.93 gf; de-awned, 66.67 gf; p < 0.01) and basal (awned, 60.45 gf; de-awned, gf; p < 0.05) spikelet positions. In addition, assessments across both growing regimes in- 64.31 gf; p < 0.05) spikelet positions. In addition, assessments across both growing regimes dicated that awn excision improved the average BTS of all 10 accessions tested, and this indicated that awn excision improved the average BTS of all 10 accessions tested, and this improvement was much higher in LT02, PI531665, and PI598788 (Figure 8). improvement was much higher in LT02, PI531665, and PI598788 (Figure 8). The structures of the abscission layers of pedicel junctions that were manually ex- The structures of the abscission layers of pedicel junctions that were manually excised cised are shown in Figure 9. Cross-sections showed that the shape and arrangement of are shown in Figure 9. Cross-sections showed that the shape and arrangement of abscission abscission layers were similar in the short-awned genotype (TZ02) for awned and de- layers were similar in the short-awned genotype (TZ02) for awned and de-awned seeds. awned seeds. For the long-awned genotype (ZNO3), the smooth fracture on the rachilla For the long-awned genotype (ZNO3), the smooth fracture on the rachilla was observed was observed in awned seeds, while a well-defined boundary between the pedicel and in awned seeds, while a well-deﬁned boundary between the pedicel and the spikelet was the spikelet was observed in de-awned seeds. observed in de-awned seeds. Figure 9. Histological structures showing variations in abscission formation in awned and de-awned Figure 9. Histological structures showing variations in abscission formation in awned and de- Siberian wildrye accessions. (a1,a2) scanning electron photos of awned (a1) and de-awned (a2) seeds awned Siberian wildrye accessions. (a1,a2) scanning electron photos of awned (a1) and de-awned of ZNO3. (b1,b2) scanning electron photos of awned (b1) and de-awned (b2) seeds of LT02. Red (a2) seeds of ZNO3. (b1,b2) scanning electron photos of awned (b1) and de-awned (b2) seeds of arrows indicate the location of the abscission layer. LT02. Red arrows indicate the location of the abscission layer. Agronomy 2021, 11, 2219 12 of 16 4. Discussion 4.1. Impacts of Awns on Seed Yield and Components The observed differences in seed yield and yield components between awned and de-awned plants were associated to the amount of assimilates partitioned to growing kernels, and were in agreement with several reports on cereal crops [18,25,26]. The removal of Siberian wildrye awns resulted in a reduced kernel weight and harvested seed yield, and this reduction was more obvious under rainfed regimes (Figure 7). Awns improved seed length, seed width, and thousand-seed weight, and this improvement compensated for the effect of reduced seeds per inﬂorescence. The signiﬁcant reduction in seed weight for de-awned plants resulted in small and shriveled seeds, and this impact was more obvious in apical and basal spikelets (Figure 4). The variation in seed size between apical, central, and basal spikelets in this species could also be associated with ﬂowering order, which starts in central spikelets, and then the top and bottom spikelets, respectively. The observed inverse association between harvested yield and shorter or non-existent awns under rainfed conditions has also been reported in wheat [27,28], barley [29,30], and rye [31]. Under irrigated conditions, long awns required a particular portion of assimilates for development, which decreased the assimilates accumulated in the kernels and thus led to a yield loss, a trade-off previously documented in several cereal crops such as wheat [8,32], barley [33], and rice [20]. Under irrigated conditions, the present study revealed that awns improved spikelet number, although this was non-signiﬁcant, compensating for the reduced fertile ﬂorets per spikelet (Figure 4). Besides, awn excision treatments signiﬁcantly reduced seed length and seed width, but this reduction was compensated for by increased fertile spikelets, which directly resulted in a higher frequency of kernels per inﬂorescence. Thus, small seed yield differences were observed for awned and de-awned plants grown under irrigated conditions. The contribution of awns on seed yield components varied across seasons. The avail- ability of soil moisture during the growing season promoted plant growth and affected seed yield components. In 2018, rainfall was lower during the vegetative growth stage but increased during anthesis and kernel development stages, resulting in a higher seed yield under the rainfed regime in this season compared to that of 2019. Similarly, Wang et al. [34] indicated that increased rainfall during the anthesis stage contributed to in- creased seed yield in Russian wildrye. Soil moisture is the key variable for the effective ﬂowering and seed development in Siberian wildrye [35], but the excessive moisture could reduce pollination, which consequently reduces the number of seed sets per spikelet. This illustrates the ﬂuctuations in seed yield per plant observed in 2019, which supports a previous study of Siberian wildrye that observed that excessive precipitation reduced seed setting rate and thus ﬁnal seed yield [5]. The estimated association of awn length with seed width and seed length was inconsistent across growing conditions, with differences in seed width being greatest in irrigated conditions and differences in seed length being greatest in the rainfed regime (Figure 3). This indicated that, as postulated by Teich [32], moisture could not always decide the impact of awns as the environments also vary in temperature, radiation, and soil fertility [32]. This is in agreement with our previous study that observed that the contribution of awns to seed yield of Siberian wildrye varied across latitudes, longitudes, and altitudes [4]. Thus, opportunity remains in the selection of awn lengths with comparable yields improvements under diverse environment conditions. 4.2. Role of Awns on Partitioning of Spike Dry Matter Dry matter accumulation in the inﬂorescence, as in leaves and stems, was thought to be associated with nitrogen supply and soil moisture content [5,36]. Although previous studies have indicated that maximum plant dry weights could be obtained by improving the photosynthetic capacity of leaves [37], the present study mirrored the capacity of awns to support dry matter partitioning into the growing kernels, especially under stress-free regimes (Figure 4). The comparisons of Siberian wildrye accessions revealed that spike dry matter was higher in the awned treatments than de-awned ones (Figure 8). Given this Agronomy 2021, 11, 2219 13 of 16 capacity of awns to increase spike assimilates, one could expect that improved spike dry weight by awns is associated with yield increase under irrigated conditions. However, awns develop rapidly under favorable conditions and impose a competing sink with growing kernels, reducing the amount of assimilates allocated to kernel ﬁlling and thus causing yield loss. This competition for assimilates between different plant organs and growing ﬂorets in the reproductive stage was previously documented in wheat. For instance, potential yield increases by spike dry weights were likely limited by the competition between growing ﬂorets and elongating stems, as reported by González et al. [38]. The capacity of awns to improve spike dry matter was non-signiﬁcant under rainfed conditions. According to Martinez et al. [39], this might be linked to limited moisture and high temperatures. Similarly, in wheat, Wang et al. [5] observed that leaf, stem, and spike dry matter contents were greatly affected by air temperature and soil moisture content. However, in the present work, the decrease in spike dry weights did not compromise the capacity of awns to improve seed yield under rainfed conditions. This was probably related to the reduction in awn lengths observed for several plants grown under rainfed conditions, reﬂecting a reduction in photosynthates allocated to those awns. The increase in assimilates allocated to growing kernels was associated with a greater increase in kernel size, especially in apical and basal spikelets (Figure 4). Overall, given the growing pressure to improve harvested yields of grass species, future yield gains should be targeted by improving spike dry matter accumulation [8]. Developing cultivars with optimum awn length will be an attractive option to improve the inﬂorescence dry weights, and thus the harvest index, in grass species. 4.3. The Impact of Awns on Seed Shattering Seed shattering is an essential adaptive trait for the efﬁcient propagation of offspring in wild plants [40]. Breeding initiatives in grasses have primarily focused on improving grain yield and biomass production rather than reducing their shattering trait, even though seed shattering has greatly hindered harvested yield in many cultivated grass species [22]. Seed shattering is a result of the progressive deterioration of the abscission layers [41], causing mature seeds to detach from the pedicel at these layers [42]. In the present study, analyses of pedicel junctions of awned plants conﬁrmed the presence of an abscission with two small cell layers (Figure 9), controlling cell separation and breakage. Moreover, the evaluation of seed shattering of awned and de-awned plants showed that awned seeds displayed a shattering trait with a complete abscission zone between the seed and the pedicel. However, the removal of awns induced a deﬁciency in the formation of the abscission zone near the vascular bundle, which caused the seeds to stay on the plant at maturity. These results indicate that long-awned species are more susceptible to shattering before harvest since awns increase seed weight and increase the axis of where the weight is concentrated, exerting additional stress on the abscission layer [22,43]. Our analyses indicated the discrepancies in the breaking tensile strength of several awned and de-awned plants (Figure 8). This illustrated how seed shattering is a highly- coordinated trait not only associated with morphological traits but also with changes in cell structure, metabolism, and gene expression [44]. Previously, a study revealed that abscission is associated with a rapid increase in cellulose and polygalacturonase activity [22]. However, how awns interact with these hormones is not clear and remains a subject of intensive investigation. The study of Magwa et al. [45] on rice indicated a possible interaction between the awn development gene (An1) and the grain-shattering- related QTL (sh4-1) on chromosome 1. Furthermore, a number of studies also showed that the expression of seed shattering may be controlled by environmental factors such as moisture and temperature [22,44]. Similarly, in this work, we observed signiﬁcant differences in seed breaking tensile strength among awned and de-awned plants across irrigated and droughted conditions (Figure 7), indicating the role of the deﬁcit and surplus of water in the expression of seed shattering in Siberian wildrye. Overall, a wide range of germplasm collections, assessments with multiple location and year testing, and both Agronomy 2021, 11, 2219 14 of 16 outdoor and greenhouse trials would be vital to better understand the inﬂuence of awns on seed shattering. 5. Conclusions This study attempted to identify the inﬂuence of awns on harvested seed yield of Siberian wildrye. The presence of awns slightly increased the seed yield per plant through increased seed size and kernel weight. Awn excision improved seeds per inﬂorescence and was associated with a reduction in seed shattering. These results revealed the advantages of growing awned species in conditions with water shortages and high temperatures, and show the existing opportunities of growing awnless grass species under stress-free condi- tions. Plant breeders should focus on increasing spikelet per inﬂorescence and the number of fertile ﬂorets through awn length manipulation. Moreover, this study revealed the possibility of improving seed production by increasing seed retention through awn length optimization. In the future, a greater number of genotypes, large ﬁeld experiments, and a divergent selection of multi-location trials and multi-year testing will facilitate the identiﬁ- cation of the further impacts of awn traits on the performance of awned grass species. Author Contributions: F.N. and Y.W. performed the ﬁeld experiment and collected the data. F.N. and W.L. analyzed the data. F.N. and W.X. wrote the manuscript. W.X. conceived and designed the research. All authors have read and agreed to the published version of the manuscript. Funding: This research was funded by The State’s Key Project of Research and Development Plan (2019YFC0507702), the Gansu Provincial Science and Technology Major Projects (19ZD2NA002), Chinese National Natural Science Foundation (31971751), the open projects of the Key Laboratory of Superior Forage Germplasm in the Qinghai-Tibetan Plateau (2020-ZJ-Y03), and the Fundamental Research Fund for the Central Universities (lzujbky-2021-ct21). Institutional Review Board Statement: Not applicable. Informed Consent Statement: Not applicable. Data Availability Statement: The datasets supporting the conclusions of this article are included within the article. Acknowledgments: The authors thank the reviewers for their thoughtful comments on an earlier version of this manuscript. 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Contribution of Awns to Seed Yield and Seed Shattering in Siberian Wildrye Grown under Irrigated and Rainfed Environments

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Agronomy – Multidisciplinary Digital Publishing Institute

Published: Nov 2, 2021

Keywords: abscission layer; awns; Elymus sibiricus; grasses; inflorescence morphology; photosynthesis; seed shattering; seed yield; yield components

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Contribution of Awns to Seed Yield and Seed Shattering in Siberian Wildrye Grown under Irrigated and Rainfed Environments

Contribution of Awns to Seed Yield and Seed Shattering in Siberian Wildrye Grown under Irrigated and Rainfed Environments

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Contribution of Awns to Seed Yield and Seed Shattering in Siberian Wildrye Grown under Irrigated and Rainfed Environments

Contribution of Awns to Seed Yield and Seed Shattering in Siberian Wildrye Grown under Irrigated and Rainfed Environments

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