Application of artificial seed technology in the production of hybrid alfalfa (Medicago sativa L.)

Alfalfa (Medicago sativa L.) is a cross-pollinated, autotetraploid crop, sold commercially as synthetic populations of plants. The production of hybrids offers the potential advantages of minimizing inbreeding depression, maximizing genetic heterozygosity, and providing a uniform, consistent phenotype, which potentially will lead to improvements in yield, persistence, disease tolerance, and quality. The use of artificial seed technology in alfalfa will allow the mass propagation of parental, self-sterile lines for the commercial production of hybrids. The ability to dry somatic embryos as artificial seeds provides the added advantages of long term germplasm storage, and international transport of pathogen free clones. The cell culture system described maximizes the production of synchronized somatic embryos, and minimizes somaclonal variation. These somatic embryos can be induced to acquire desiccation tolerance by treatment with ABA or any one of several environmental stresses, including water and nutrient stresses, if applied to the embryos at the cotyledonary stage of development. The embryos have been subsequently air dried slowly (over 7 days) or rapidly (over 1 day) to moisture contents less than 15% water and remain fully viable. Dry somatic embryos have been stored with no loss of viability for 8 months at room temperature and humidity. Dry somatic embryos are germinated on moist germination paper and follow a similar developmental pattern to seedlings from true seed, but are less vigorous. The development of populations of alfalfa which carry genes for regeneration as well as having suitable agronomic characteristics is possible using conventional plant breeding methods.