Clonal True-to-Type Verification of Potato Accessions Retrieved from In Vitro Conservation and

Twenty potato (Solanum tuberosum L.) accessions were retrieved from three to five years (without subculturing) in vitro storage, and 18 from 1-year cryopreservation. Using 23 morphological descriptors, all accessions were compared with original clones to verify if they were true-to-type. Materials from in vitro storage were compared with clones maintained in the field, and those from cryopreservation with clones maintained in vitro. Comparison of cryopreserved materials was made using three types of propagules (plantlets, stem cuttings, and tubers). Additionally, accessions from in vitro storage were compared with samples maintained in the field using 14 highly polymorphic potato microsatellite markers. Six accessions (four from in vitro storage and two from cryopreservation) showed differences in multiple morphological characters, suggesting a case of misidentification. In the remaining acces-sions, differences were observed for 10 descriptors of flowering degree and color expression. Fewer accessions showing differences (four) were found when tubers were used as planting material. Simple sequence repeats (SSR) analysis of 20 accessions, retrieved from in vitro storage and compared with original clones, resulted in five accessions showing remarkable DNA differ-ences, again revealing possible misidentifications. Four were found different from the original clones by morphological and molecular analyses; and, one accession was found different at the molecular level, even though it showed no morphological differences. Plant genetic resource conservation at CIP (Golmirzaie and Panta, 1997a) focuses on complementary in vitro approaches, with linkages to in situ conservation. The former uses tissue culture and cryo-preservation techniques, as well a