RECOVERY OF WHOLE PLANTS OF SWEET ORANGE FROM SOMATIC EMBRYOS SUBJECTED TO FREEZING-THAWING TREATMENTS

Freezing/thawing conditions for cryopreservation of somatic embryos of 'Washington Navel' sweet orange (Citrus sinensis (L.) Osb.) were evaluated. No survival of fast-cooled embryos occurred regardless of the thawing method. Embryos subjected to slow cooling at an estimated rate of 0.5-degrees-C min-1 down to -42-degrees-C followed by immersion in liquid nitrogen survived. Survival rate depended on the thawing method. An average survival of 30.5% was achieved when frozen embryos were thawed by immersion in a water bath at 37-degrees-C. Surviving embryos developed into whole plantlets and no phenotypic abnormalities have been observed during a growth period of four years. Total soluble proteins and peroxidase and esterase isoenzyme analysis did not show differences between treated plants and non-frozen controls.