Alfalfa (Medicago sativa) is a species of legume grown in many regions of the world as a source of animal fodder, due to its high protein content and biomass yield. Moreover, this so-called “King of Grass” is hailed as an environmentally beneficial crop, with proven positive impacts on biodiversity and soil nitrogen conservation. More recently, alfalfa protein has also been used in aquaculture, pet food industry, and even human diet.
Alfalfa produces two types of seeds – hard and non-hard – which cannot be clearly distinguished from visual observations alone. Since they exacerbate slow germination, nonuniform seedling establishment, increased weed competition, and germination failure, hard seeds have low value and pose major challenges from an economic standpoint.
To better understand the characteristics of alfalfa hard seeds, a team of scientists led by China Agricultural University (CAU) has investigated a phenomenon called “seed dormancy,” referring to the delayed germination following embryogenesis. Dormancy has several components thought to influence seed germination, including hormone-mediated physiological dormancy (PD), hard seededness for physical dormancy (PY), and combinatorial dormancy (PY+PD).
Until recently, scientists believed that dormancy in alfalfa included only the PY type. However, by combining multispectral imaging (MSI) technology with “multi-omics” (transcriptomics, metabolomics, and methylomics) platforms, the experts now found that alfalfa dormancy is also structured by the PY+PD pattern.
“Studying dormancy in hard and non-hard alfalfa seeds is problematic. Doing comparative research by soaking the seeds in water–a technique called imbibition–is time-consuming and causes the non-hard seeds to germinate. We needed an accurate, non-destructive, and high-throughput approach to gain deeper insights,” said senior author Shangang Jia, an associate professor of Genomics and Bioinformatics at CAU.
By combining MSI with multi-omics platforms, Jia and his team developed such a high-throughput technique for identifying seeds, comparing dormancy patterns, and clarifying differences in physiology, gene expression, and metabolism in both hard and non-hard alfalfa seeds.
“The technique could successfully identify hard alfalfa seeds with high accuracy – of up to 100 percent. Furthermore, the transcriptomics, metabolomics, and methylomics analyses revealed that abscisic acid (ABA) responses played a key role in hard alfalfa seeds,” Jia explained.
ABA is a hormone that induces dormancy and keeps seeds in a dormant state, often in combination with other hormones such as indole acetic acid (IAA) and jasmonic acid (JA). The researchers found that, compared to non-hard seeds, hard seeds contained higher levels of antioxidants, flavonoids, lipids, and hormone biosynthetic pathways. Moreover, the increased expression of ABA genes, along with the differential methylation of ABA-responsive genes in hard seeds, seemed to underscore the ABA responses.
By identifying non-PY hard seeds containing higher ABA/IAA and ABA/JA levels that did not germinate following an intervention to break dormancy, the experts found further evidence that the PY+PD rather than the PY pattern alone leads to the germination failure of hard seeds.
“We believe we’ve provided a theoretical and technical framework for exploring alfalfa hard seed dormancy, and our findings could certainly guide the optimal processing of these seeds in the alfalfa seed industry,” Jia concluded.
The study is published in The Crop Journal.
Alfalfa is a perennial legume crop that has several unique and valuable qualities, which make it special:
Alfalfa is an excellent source of various nutrients, including protein, fiber, vitamins (A, C, E, and K), and minerals (calcium, potassium, phosphorus, and iron). This makes it a valuable feed for livestock and a dietary supplement for humans.
As a legume, alfalfa has the ability to form a symbiotic relationship with nitrogen-fixing bacteria (Rhizobium) in its root nodules. This process allows alfalfa to convert atmospheric nitrogen into a usable form for plant growth, reducing the need for synthetic nitrogen fertilizers and improving soil fertility.
Alfalfa has a deep and extensive root system, which allows it to access water and nutrients from deeper soil layers. This characteristic makes it drought-tolerant and enables it to contribute to soil stabilization and erosion control.
Alfalfa is a versatile crop with various applications. It is primarily used as high-quality forage for livestock, such as cattle, horses, sheep, and goats. It can also be processed into pellets, meal, or cubes for animal feed. In addition, alfalfa can be used as a green manure or cover crop to improve soil structure, suppress weeds, and increase organic matter content.
Alfalfa has potential as a feedstock for producing bioenergy, such as biofuels and biogas, due to its high biomass yield and relatively low input requirements.
Alfalfa has been used in traditional medicine for centuries to treat various ailments, including digestive disorders, kidney and bladder issues, and arthritis. It is also believed to have antioxidant, anti-inflammatory, and immune-boosting properties. However, more research is needed to confirm these claims.
Alfalfa is an important source of nectar and pollen for pollinators, such as bees and butterflies, which play a crucial role in maintaining biodiversity and supporting food production.