Morphological and isozyme characterization of common papaya in Costa Rica

To study the potential of Costa Rican indigenous germplasm for the genetic improvement of the common papaya, 32 feral, seven home garden and seven commercially cultivated plants were sampled for in situ morphological and/or isozyme characterization. A list of 28 quantitative and 30 qualitative traits was used for vegetative and floral parts. Considerable variation was observed for fruit traits, from typical wild types (very small seedy fruits with thin yellow mesocarp) to commercial fruits (medium to large fruits with abundant orange or reddish pulp). The former were more common along the Pacific Coast, while introgression between wild and cultivated materials appeared more common on the Caribbean side. Hermaphroditism was not observed in feral populations. All these unimproved materials were also clearly differentiated from commercial cultivars by larger leaves and petioles, with less marked leaf divisions, presence of bracts, and smaller flowers. Analysis of variance showed a significant sex effect on length and lobulation of the leaves. Four isozyme systems, out of eight allowing good resolution, revealed polymorphism. However, only eight different zymotypes could be identified. Cluster analysis did not allow detection of any geographic structuration neither in morphological diversity nor in isozyme diversity, despite the cordilleras separating the Pacific and Caribbean coasts, which gives a new example of the contrast between the wide morphological variation and the poor genetic diversity observed in the common papaya.