Inter- and intra-specific variation in fruit biomass, number of seeds, and physical characteristics of seeds in Opuntia spp., Cactaceae

Domestication is an evolutionary process that culminates with the origin of individuals or populations that are morpho-physiologically, chemically and genetically different from their wild, congeneric relatives. The aim of the present study was to quantify the inter- and intra-specific variation in fruit biomass, number of seeds, and physical characteristics of seeds in O. streptacantha Lem., O. hyptiacantha F.A.C. Weber, O. megacantha Salm-Dyck, O. albicarpa Scheinvar and O. ficus-indica (L.) Mill., the least, intermediate, and most highly domesticated species. The hypothesis was that selecting larger fruits with fewer and softer seeds (normal and aborted) during domestication reduced the interspecific variation in fruit biomass, number of seeds, and physical characteristics of seeds in Opuntia spp., Cactaceae. For fruits of 89 variants of the Southern Mexican Plateau, total biomass and biomass of pulp with seeds was quantified; seed length, width, thickness and dehydrated mass were measured, as well as hardness of normal seeds. The total number of seeds was quantified and normal and aborted seeds were counted separately. A randomized design, with 89 treatments (variants) and six replicates and a fruit as experimental unit per treatment was used. The data were analysed by ANOVA, Tukey’s multiple comparison test (p ≤ 0.05), multivariate ordination (principal components analysis) and classification (clustering analysis). Inter-specific analysis indicated that fruits of the most highly domesticated variants (O. albicarpa and O. ficus-indica) had higher biomass (p ≤ 0.05), followed by those of O. hyptiacantha and O. megacantha and wild variants of O. streptacantha, and non-significant differences existed in seed thickness or hardness. Fruit and pulp biomass were positively and significantly correlated with seed biomass. Species with greater domestication clustered according to their larger fruits (≥117.83 g) and the greater number of aborted seeds (≥65). Domestication of Opuntia has also modified seed dimensions and increased the number of aborted seeds per fruit (≤11 to ≥65).