Submitted to: Genetic Resources and Crop Evolution
Publication Type: Trade Journal
Publication Acceptance Date: February 25, 1999
Publication Date: N/A
Interpretive Summary: Carica L., comprising twenty-one species is largest of five genera in the family Caricaceae with domesticated C. papaya, which is economically important throughout the tropics and subtropics. A survey of allozyme diversity in genus Carica documented low levels of variation. Genetic variation for resistance to viral and fungal diseases is low in domesticated papayas, motivating the search for wild relatives with resistance. The level of speciation and evolutionary relationships within the genus remain unclear, a better understanding is needed for effective use of germplasm for genetic studies and horticultural improvement. Restriction fragment length variation was analyzed to examine evolutionary divergence and phylogenetic relationships among Carica species. The most striking result of analysis was that C. papaya formed a distinct clade separate from the rest of Carica. This indicates that evolution in genus Carica is not strictly monophyletic; other Carica species share fewer synapomorphies with papaya than related Jarilla mexicana. Papaya had an early divergence from the rest of the South American species and continued to evolve in isolation, from the rest of Caricaceae, probably in Central America. A more detailed picture of the evolution within these groups must await broad morphological and molecular based cladistic studies involving all twenty-one species of Carica.
The phylogenic relationships among twelve wild and cultivated species of Carica (Caricaceae) were analyzed using restriction fragment length variation in a 3.2 kb PCR amplified intergenic spacer region of the chloroplast DNA. A total of 138 fragments representing 137 restriction sites accounting for 5.8% of the amplified region were examined. Both parsimony and neighbor joining cluster analyses confirmed the close association among South American wild Carica species. However, cpDNA analyses showed two basic evolutionary lineages within the genus Carica, one defined by cultivated C. papaya and another consisting of the remaining wild species from South America in a well resolved but poorly supported monophyletic assemblage. This evolutionary split in Carica strongly suggests that C. papaya diverged from the rest of the species early in the evolution of the genus and evolved in isolation, probably in Central America.