Morphological Seeds Descriptors for Characterize and Differentiate Genotypes of Opuntia (Cactaceae, Opuntioideae)

Aims: In this paper, a morphometric study was carried out to analyze the variation of seeds of Opuntia accessions using several statistical approaches. The main objective was to select morphological seeds variables for characterization and differentiation of Opuntia genotypes.
Place and Duration of Study: The research was conducted in Crops Science Department of the Chapingo Autonomous University, Mexico. The sample collection was down in 2012. Seed data was obtained during 2013.
Methodology: A total of 110 Opuntia accessions (some classified and other ones with no specific taxonomic assignation), one accession of Cylindropuntia sp. (Cactaceae, Opuntioideae) and two other outgroups (Cactaceae, Pachycereae) were used. Nineteen internal and external seeds variables were obtained using image analysis. Basic statistical analysis, analysis of variance, principal component analysis, cluster and discriminant analysis were performed.
Results: Highly significant differences among accessions for all seed characters were showed. The most of the variables showed a coefficient of variation less than 10%. From de 19 variables studied, two variables did not contribute significantly to discriminate between accessions as determined by Step wise Discriminant Analysis. The principal components analysis showed that the first three components accounted for 83.35% of the variability; the first component contributed twice the variability (48.12%) respect to the second one (23.77%). Tukey's test determined that the Feret diameter and seed area were the most discriminating variables between the 7 groups resulting from de cluster analysis.
Conclusion: The selected variables, using several statistical approaches, were of interest for the characterization and identification of the different Opuntiageno types. The morphological seed characteristics responsible for the separation between genotypes were Area, Major Axis Length, Minor Axis Length, Feret Diameter and Weight. These variables have a high discriminatory power and can be taken into account as potential parameters for genotypes assignation within the Opuntia genus.