Analysis of genetic diversity in Agave tequilana var. Azul using RAPD markers

By federal law in Mexico, A. tequilana Weber var. Azul is the only variety of agave permitted for the production of any tequila. Our objective was to assay levels of genetic variation in field populations of A. tequilana var. Azul using randomly amplified polymorphic DNA (RAPD) markers. Ten plants w ere collected from each of four different fields, with two fields being loc ated in each of two principal regions of Mexico for the cultivation of A. t equilana var. Azul. The two regions are separated geographically by approxi mately 100km. Genetic relationships between A. tequilana var. Azul and two other varieties of A. tequilana Weber, 'Chato' and 'Siguin', were also inve stigated using RAPDs. Among the three varieties, 19 decamer primers produce d 130 markers, of which 20 (15.4%) were polymorphic between A. tequilana va r. Chato and A. tequilana var. Siguin. The results of RAPD analysis suggest that A. tequilana var. Siguin is more closely related to A. tequilana var. Azul than is A. tequilana var. Chato. Among the 40 field selections of A. tequilana var. Azul, only 1 of 124 RAPD products (0.8%) was polymorphic and 39 of 40 plants were completely isogenic. This is one of the lowest levels of polymorphism detected to date for the analysis of a crop species, and i s proposed to be the result of the promotion of a single conserved genotype over many years due to an exclusive reliance on vegetative propagation for the production of new planting materials. The significance of these result s is discussed in relation to breeding programs focused on the improvement of A. tequilana var. Azul.