EFFECT OF CARBOHYDRATE SOURCE ON ALFALFA SOMATIC EMBRYOGENESIS

Cultures of alfalfa (Medicago sativa L. clone RA-3) were screened for their response to a wide variety of carbohydrate sources, in the presence or absence of sucrose. Maltose, maltotriose, and soluble starch all act to improve the morphology and eventual conversion to plantlets of somatic embryos. Glucose, sucrose, and other carbohydrates do not have a similar effect. Additional studies were carried out with maltose since this carbohydrate also gives the highest embryo yield. The concentration optimum for maltose is about 4% (w/v). Maltose acts independently of sucrose and in a way which suggests that it serves as a nutritional, rather than as an osmotic, effector of embryogenesis. The effect of maltose on embryogenesis is dependent on the presence of NH4+ whose optimum is approximately 15 mM. Embryogenesis on maltose will not occur in the absence of NH4+. A highly effective regeneration medium can be achieved by including NH4+ and amino acids, especially proline, in a maltose-containing regeneration medium. Maltose is also useful in increasing embryo formation in genotypes which show low regeneration.