Submitted to: Euphytica
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/22/2000
Publication Date: 3/1/2001
Citation: VEGA, K.G., GONZALEZ, M., MARTINEZ, O., SIMPSON, J., VANDEMARK, G.J. ANALYSIS OF GENETIC DIVERSITY IN AGAVE TEQUILANA USING RAPD MARKERS. EUPHYTICA, 119:(3):335-341. 2001. Interpretive Summary: Tequila is the most widely recognized export product of Mexico, and great efforts have been taken to ensure the quality of the product. By federal law in Mexico, A. tequilana Weber var. Azul is the only variety of agave permitted for use in the production of tequila. Unfortunately, it takes anywhere from between 7-10 years of growth in the field before a plant of the variety Azul can be harvested, and the variety is susceptible to many diseases that result in considerable economic losses. One way to develop varieties that are more resistant to disease and can be harvested in less time is to make improvements with plant breeding. Before plants can be included in a breeding program, it is essential that it is known that the plants to be included are genetically distinct from each other. We conducted a survey of plants of A. tequilana var. Azul grown in different fields in the two principal growing regions of Mexico. We found that plants grown in fields seperated by over 60 miles were nearly genetically identical. We found that the plants included in our analysis comprised one of the most genetically uniform populations ever encountered in the history of evaluating plant populations for genetic diversity. These results will help growers to identify environmental and cultural causes of differences between plants, since the all the plants have nearly identical genetic makeups. The results also will highlite to producers the need to immediately initiate a long term breeding program focused on the genetic improvement of the agave variety Azul.
Technical Abstract: By federal law in Mexico, A. tequilana Weber var. Azul is the only variety of agave permitted for the production of 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 were collected from each of four different fields, with two fields being located in each of two principal regions of Mexico for the cultivation of A. tequilana var. Azul. The two regions are seperated geographically by approximately 100km. Genetic relationships between A. tequilana var. Azul and two other varieties of A. tequilana Weber, ¿Chato¿ and ¿Siguin¿, were also investigated using RAPDs. Among, the three varieties, 19 decamer primers produced 130 markers, of which 20 (15.4%) were polymorphic between A. tequilana var. 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 is 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.