Discriminant Analysis of Morphological Descriptors to Differentiate the Opuntia Genotypes

In the present paper statistical procedures are considered to monitor the discriminating ability of descriptor variables, designed to characterize Opuntia spp. accessions, with the aim of identifying the most discriminating traits and provide a list of morphological characters of highest priority within the descriptors. Data from a set of 71 accessions of Opuntia spp. collected in 3 years of experimentation at the germplasm collection set up in Italy by the University of Sassari were analyzed. Accessions were characterized using 38 morphological descriptors evaluated in plant, cladodes and fruit, included in the FAO 'Descriptors for Cactus pear (Opuntia spp.)'. A discriminating analysis using a stepwise method was carried out to analyze the classificatory quantitative descriptors. For the qualitative descriptors, statistical comparisons were done by means of the chi-square (chi(2)) test. According to the analysis performed, only few descriptors have shown an effective discriminating capacity. Three quantitative fruit descriptors (recepticular scar diameter, seed number and pulp weight) and seven qualitative descriptors (cladodes shape, spines, fruits number, fruits size, recepticular scar position, peel and pulp colour) have been identified as differential parameters in Opuntia ficus-indica and O. amyclaea. However, a considerable number of descriptors among the 38 examined are relevant for the purpose of describing accessions and identifying traits connected to specific uses. Morphological characterization is needed to provide users valuable information on individual accessions, relationship among traits, and the structure of collections.