Awns, needle-like structures formed on the distal of the lemmas in the florets, are of interest because of their essential roles in seed dispersal, germination and photosynthesis. Previous research has reported the potential benefits of awns in major cereal grasses, yet reports on the agronomic and economic implications of awn length variation in forage grasses remain scarce. This study investigated the variation of awn length among 20 Siberian wildrye populations and the effect of awn length on seed yield and yield components. This work then studied the impact of awn length on seed dispersal and germination. The analyses indicated a high level of awn length variation among populations. Awn length showed a significant influence on harvested seed yield per plant (p < 0.05) mostly driven by interactions between awn length and the majority of seed yield components. Principal component analysis clearly revealed that the final impact of awn length on seed yield depends on the balance of its positive and negative effects on traits determining seed yield. Furthermore, awn length tended to increase seed dispersal distance, although little diversity in the nature of this progression was observed in some populations. Awn length exhibited a significant relationship (p < 0.05) with germination percentage. It also tended to shorten germination duration, although this interaction was not statistically significant. Collectively, these results provide vital information for breeding and agronomic programs aiming to maintain yield in grasses. This is the first report to demonstrate in Siberian wildrye the agronomic impacts of awn length variation.

Awns, which are either bristles or hair-like outgrowths of lemmas in the florets, are one of the typical morphological characteristics of grass species. These stiff structures contribute to grain dispersal and burial and fend off animal predators. However, their phenotypic and genetic associations with traits deciding potential yield and quality are not fully understood. Awns appear to improve photosynthesis, provide assimilates for grain filling, thus contributing to the final grain yield, especially under temperature- and water-stress conditions. Long awns, however, represent a competing sink with developing kernels for photosynthates, which can reduce grain yield under favorable conditions. In addition, long awns can hamper postharvest handling, storage, and processing activities. Overall, little is known about the elusive role of awns, thus, this review summarizes what is known about the effect of awns on grain yield and biomass yield, grain nutritional value, and forage-quality attributes. The influence of awns on the agronomic performance of grasses seems to be associated with environmental and genetic factors and varies in different stages of plant development. The contribution of awns to yield traits and quality features previously documented in major cereal crops, such as rice, barley, and wheat, emphasizes that awns can be targeted for yield and quality improvement and may advance research aimed at identifying the phenotypic effects of morphological traits in grasses.

The identification of biological mechanisms underlying the development of complex quantitative traits, including those that contribute to plant architecture, yield and quality potential, and seed dispersal, is a major focus in the evolutionary biology and plant breeding. The awn, a bristle-like extension from the lemma in the floret, is one of the distinct morphological and physiological traits in grass species. Awns are taught as an evolutionary trait assisting seed dispersal and germination and increasing photosynthesis. Awn development seems to be complex process, involving dramatic phenotypic and molecular changes. Although recent advances investigated the underlying morphological and molecular genetic factors of awn development, there is little agreement about how these factors interact during awn formation and how this interaction affects variation of awn morphology. Consequently, the developmental sequence of the awn is not yet well understood. Here, we review awn morphological and histological features, awn development pathways, and molecular processes of awn development. We argue that morphological and molecular genetic mechanisms of awn development previously studied in major cereal crops, such as barley, wheat, and rice, offered intriguing insights helping to characterize this process in a comparative approach. Applying such an approach will aid to deeply understand factors involved in awn development in grass species.

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 awns on Siberian wildrye seed production, awn excision analyses from 10 accessions were performed at flowering stage under irrigated and rainfed regimes. Overall, awn excision reduced thousand-seed weight and seed size under both irrigated and rainfed regimes, which decreased final seed yield per plant. De-awned plants produced significantly more seeds per inflorescence, but spikelets per inflorescence was not influenced by awn excision in either condition. Moreover, histological analyses showed a high degradation of the abscission layer in the awned plants than de-awned ones, and awn excision evidently improved average seed breaking tensile strength (BTS), and thus decreased the degree of seed shattering. In conclusion, the observed significant impact of awn excision on 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 producers, and researchers to efficiently improve seed production in Siberian wildrye.

Contribution de la diversité de gènes du développement reproducteur à la variabilité morphologique de la panicule chez le riz: Le riz africain, Oryza glaberrima Steud., une espèce cultivée étroitement apparentée au riz asiatique (Oryza sativa L.), est une ressource précieuse pour l'amélioration des propriétés de résistance biotique et abiotique dans la culture du riz. Bien que des recherches approfondies aient été menées sur les bases génétique de l'architecture de l’inflorescence ou panicule chez O. sativa, les facteurs génétiques et moléculaires régissant ce trait essentiel chez O. glaberrima restent mal compris. De plus, il y a un manque de connaissances complètes concernant la diversité intra- et inter-spécifique du développement et de l'architecture de la panicule en relation avec la domestication et la diversification des espèces de riz. Pour combler ces lacunes, nous avons utilisé un panel d'associations composé de 247 espèces de riz africaines, englobant à la fois des génotypes cultivés et sauvages. Tout d'abord, grâce à des analyses in silico et à une analyse d'association basée sur les gènes candidats de 78 gènes connus pour être associés au développement reproducteur, nous avons identifié des variants de séquence naturels sur 27 gènes orthologues chez O. glaberrima qui sont associés de manière significative aux traits liés à la panicule et au temps de floraison. Notamment, nous avons identifié les variants significatifs dans le promoteur et/ou la séquence codante des orthologues de INDETERMINATE SPIKELET 1 (IDS1), ABERRANT PANICLE ORGANIZATION 2 (APO2) et CCT22, qui sont impliqués dans le temps de floraison et/ou la morphologie paniculaire chez O. sativa. Dans un deuxième temps, en utilisant une analyse d'association à l'échelle du génome, nous avons identifié un total de 41 régions génomiques stables qui sont significativement associées aux traits morphologiques de la panicule, dont 13 co-localisées avec des QTL précédemment identifiés dans les populations d'O. sativa et 28 étaient uniques pour cette population d’O.glaberrima. De plus, nous avons trouvé une région génomique d'intérêt sur le chromosome 3 qui était associée au nombre d'épillets et de branches primaires et secondaires. Dans cette région, a été localisé l'orthologue du gène PHYTOCHROME B d’O. sativa (Oglab_006903/OgPHYB), possédant des allèles associés à la diversité du temps de floraison et du nombre d'épillets par panicule. Enfin, nous avons analysé les variants structuraux (SV, pour « structural variants ») présents dans les 41 sites GWAS et identifié des SV ancrant des gènes clés associés au développement paniculaire, d'autres portant de nouveaux gènes spécifiques à O. glaberrima. Les résultats de cette étude contribuent à une meilleure compréhension des facteurs génétiques et moléculaires sous-jacents à la diversité du développement et de l'architecture de la panicule de riz et offrent des cibles potentielles pour améliorer les traits morphologiques de la panicule de cette culture importante.