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 eval uated. No survival of fast-cooled embryos occurred regardless of the t hawing 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 t hawed by immersion in a water bath at 37-degrees-C. Surviving embryos developed into whole plantlets and no phenotypic abnormalities have be en observed during a growth period of four years. Total soluble protei ns and peroxidase and esterase isoenzyme analysis did not show differe nces between treated plants and non-frozen controls.