Phenotypic analysis of mezcal agaves from the Central Valleys of Oaxaca

Abstract

ABSTRACT

Objective: Mezcal agaves are currently considered of high economic value in the state of Oaxaca, due to the demand for mezcal production, therefore, this research aims to highlight the importance of morphological diversity within and between cultivated Agave species.

Design/methodology/approach: A completely randomized experimental design with 10 treatments (populations) and 11 repetitions (individuals) was used. The experimental unit consisted of a plant (individual), where 19 morphological descriptors proposed by the National Seed Inspection and Certification Service (SNICS) were evaluated. 275 individuals of the species Agave angustifolia, Agave karwinskii, Agave marmorata, Agave rhodacanta, Agave potatorum, Agave semanniana and Agave nussaviorum were evaluated through a multivariate analysis, determining the phenotypic variability and the relationships between them.

Results: By means of a cluster analysis, dendrograms corresponding to the grouping mode Q and mode R were made, forming 7 groups, based on the average linkage generated from the standardized MBD of the species of the genus Agave sampled. Creating a heat map, the relationships between the species and the qualitative and quantitative variables evaluated were clearly and practically observed. Using the k-means method, 5 groups were formed. This  technique clearly represents the groupings of the different species according to what was sampled in the field and what was consulted in the taxonomic bibliography. Through a Principal Component Analysis (PCA) it was determined that the first two principal components explain 55.99% of the total variation. For CP1 and CP2, the variables with the greatest contribution were those related to the shape of the leaf (Fh), size of the lateral spine (Tel), number of leaves (Nh), plant height (H), uniformity of the size of the spine (UTE) and the shape of the terminal spine (FET).

Limitations on study/implications: For a complete study, it is necessary to carry out taxonomic keys to identify species, subspecies and even varieties of Agave, in addition to carrying out a molecular characterization to understand the variability and phylogenetic relationships of these populations, through a phylogenetic analysis.

Findings/conclusions: Three species under culture conditions showed high phenotypic variability in the maturation phase according to multivariate analysis techniques. The potatorum and karwinskii varietal complexes showed the greatest intra-population phenotypic variability, with significant differences in the same species. Agave marmorata was the group that did not show intra-population and inter-population variability, with a single variable that explained the variation (leaf textura, Txh), it is a tall species and larger in diameter than the other species. In the case of the Mexican group (Agave rhodacantha), the variables in that group not showed high correlation in the PCA analysis, nor with another method used, since they behaved very dispersed. In the case of these groups of populations, it is necessary to carefully evaluate the variables obtained in the field to correlate the variables in PCA and k-means and verify the behavior of this group.

Keywords: Morphological diversity, multivariate analysis, cluster, k-means, PCA.