Caracterización morfológica y molecular de poblaciones de aguacate cascarudo

Abstract

The Persea genus is composed of two subgenus; Persea and Eriodaphne, the Persea subgenus to which avocado belongs, is considered the largest of the genetic variability and the most complex in evolutionary terms of the Lauraceae Family. In the State of Mexico in the municipalities of Ixtapan del Oro and Zumpahuacán, avocados have been identified as “cascarudos” with morphological attributes different from those of known species of the Persea subgenus, however they have similarities in pubescence on the underside of the leaf to Persea floccosa and thickness of the fruit shell to Persea tolimanensis, additionally are distributed in a habitat where Persea americana var drymifolia grows, this last known as Mexican race distinguishable by its thin skinned. Thus, in order to have more knowledge about their description and distribution, the objective of this study was to differentiate morphologically and molecularly the “cascarudo” individuals from two regions of the State of Mexico and establish relationships with species and races from subgenus Persea. The morphological characterization was carried out through the use of 64 characters of which 19 were quantitative and 45 qualitative obtained from the guidelines of IPGRI (1995) and UPOV (2006). Molecular characterization was performed using the RAPD and ISSR markers, the CTAB method was used for DNA extraction and through columns with the commercial kit FAST (ID) ®. The DNA was amplified by PCR with 8 RAPD markers and 6 ISSR markers and the products obtained were visualized on agarose gels. Through the discriminant and cluster analysis, it was found that the pubescence density, shape and undulation of the leaf grouped the individuals of the study close to reference species while shell thickness, anise smell, sepal width and density of the leaf Leaf pubescence effects a separated them. The dendograms obtained with molecular markers generated clusters by means of Neighbor-joining construction method and distance of similarity using the Jaccard index with a resampling of 1000 repetitions for RAPD, for ISSR was used the UPGMA clustering method and the Jaccard index. It was generated a 99% of polymorphisms, 1417 bands of 250 to 900 bp with RAPD and 917 bands of 200 to 1000 bp for ISSR with a polymorphic information content (PIC) of 0.45 and 0.49 and a resolution power of 8.8 and 5.81 respectively. Morphological and molecular characterization provided evidence that avocado “cascarudo” could represent Página | vii a natural hybrid between regional old genotypes with P. floccosa, P. americana var. drymifolia and P. americana var. guatemalensis.