Tracing the geographic origins of two forms of Opuntia ficus-indica cultivated in Argentina using haplotype diversity patterns, and cytogenetic and morphological analyses

Abstract

Opuntia ficus-indica, commonly known as prickly-pear, tuna, or nopal, is a cactus species of economic significance. It is widely cultivated for its fruits and cladodes, used as both fodder and human food. The species would have been domesticated in pre-Hispanic Mexico. In Argentina, two forms are present: the horticultural (spineless, f. ficus-indica) and the wild (spiny, f. amyclaea) forms. The presence/absence of spines would be a genetically controlled trait; thus, the species would have been introduced more than once in our country. A molecular and cytogenetic study was conducted to characterize the genetic variability, infer the source of introduction in Argentina, and explore the relationship between morphotypes. Most spine samples had the Q16-H1 haplotype, except for samples from Mexico, Santiago del Estero, and Catamarca. Samples from Salta, Santiago del Estero, and Catamarca showed morphological differences from O. ficus-indica. The cytological analysis revealed that most populations are octoploid, except for one diploid population from Mexico. Although the number of individuals from Mexico was low, haplotype diversity and number of diploid individuals was higher in that country than in Argentina. The occurrence of a single haplotype of the species associated with both spineless and spiny forms in Argentina reveals a single introduction event and its subsequent dispersion mainly through asexual reproduction. The haplotype diversity found in Argentina is probably due to hybrids between O. ficus-indica and Opuntia species native to this country.