Genetic Variability in Carcia Papaya and Related Species

Abstract

As part of an ex situ conservation of Carica germplasm in Hawaii, expeditions in 1992 and 1993 resulted in the collection and analysis of seeds of 131 accessions of Carica papaya from 9 countries in Central and South America (Mexico, Belize, Guatemala, Honduras, Costa Rica, Panama, Venezuela, Colombia, and Ecuador). Populations of wild small-fruited C. papaya (previously designated as C peltata), and hybrids between the wild and domesticated were sampled from their native range on the Caribbean coast of Central America (Mexico, Belize, Guatemala, Honduras). Domesticated C. papaya specimens were also collected from Central and South America. The three types of C. papaya were examined for variability in nine enzyme systems (ACO, IDH, MDH, PGM, PGI, SKD, TPI, UGP, and 6-PGD) and 13 loci. Domesticated, hybrid, and wild C. papaya shared a Nei’s genetic identity. I, of greater than 0.9, which is consistent with conspecific populations. The intrapopulational genetic variability results indicate that the greatest diversity exists in the Yucatan-San Ignacio-Peten-Rio Motagua area in Central America. In general, the wild C. papaya populations have greater isozyme variability than the domesticated populations. The hybrid populations have intermediate variability between the domesticated and the wild populations. The least diverse populations are found in South America where no wild populations are found. Carica cauliflora, C. goudotiana, C. crassipetala, C. sphaerocarpa, C. pubescens, C. microcarpa ssp. baccata, C. microcarpa ssp. heterophylla, C. microcarpa ssp. microcarpa, C. stipulata, C. pulchra, and the natural hybrid C. X heilbornii n.m. pentagona (babaco) were collected in Venezuela, Colombia, and Ecuador. Carica glandulosa, C. monoica, C. parviflora, and C. quercifolia were obtained from germplasm banks in Latin America or were already present in the USDANCGR collection. Isozyme analysis indicated that C. papaya is distantly related to the other Carica species included in this study and that none of the other Carica species could have been a wild progenitor of C. papaya in the recent past. Recommendations on future collecting expeditions and conservation of Carica genetic resources are suggested.