From encapsulated somatic embryo to plantlet regeneration

Growth conditions (growth substratum, maturation and sucrose supply) for the regeneration of encapsulated somatic carrot embryos into plantlets were tested. The germination rate and frequency of morphologically normal and abnormal plantlets were recorded Germination rates were high (80-95%) and identical in all growth substrata. There was no conversion into plantlets on the liquid medium. The total conversion rates into plantlets on agar and sand were the same (35%-40%), but there were significant differences in the rate of conversion into morphologically normal plantlets (20% on agar and 40% on sand), due to secondary embryogenesis on the agar, Rates of conversion into normal plantlets were still lower when a maturation step was included prior to sowing. The time required for seedling development was much longer than for seedlings from natural seeds. Plantlet production from these embryos also requires a carbohydrate supply in the growth medium. Thus, regeneration should not be evaluated by the germination rates alone, but by the rate of conversion into normal plantlets. A sterilized sand growth substratum supplied with carbon and other nutrients appears to be most appropriate for plant regeneration.