Morphological and biochemical analyses were carried out to characterize the selected papaya (Carica papaya L.) inbreds and hybrids and to assess genetic relatedness among them. Transmission of morphological traits showed evidence of Mendelian inheritance. Cluster analysis using morphological characters successfully divided the papaya accessions into two groups. The first group (5648, Solo and their hybrid B) had yellow flesh, green petioles, approximately similar percent edible portions and had the smallest fruits. As for isozyme analysis, 13 loci were scored of which eight were polymorphic. It can be inferred from the gel banding patterns that fixation is not complete in the inbred parents and that they still maintain a high level of heterozygosity. Cluster analysis using isozyme data divided the papaya accessions into four groups with the foreign introductions 5648, 5893 and Solo making up the first three groups and the remaining papaya accessions the other. It was also revealed that some inbreds presumably of very diverse origins exhibited similar morphological and isozyme features, raising the possibility that they have phylogenetic affinities and/or common origins. This low variability of the papaya genotypes studied could be due to the combined effects of migration, human selection for PRSV-tolerant varieties and genetic drift due to the few surviving strains left to interbreed after widespread PRSV infestation in the early 1980s. This study provides plausible yet tentative explanation to the low genetic diversity in C. papaya that can be verified with a more extensive study using more papaya accessions and more morphological and biochemical markers.

Key words: Carica papaya L., inbreds, hybrids, Solo, Sinta, Giliw, PRSV-tolerant varieties, morphological characterization, isozyme, genetic diversity, cluster analysis