Agave: What DNA Reveals

For over two decades, experts have raised concerns about the genetic diversity of Tequilana Weber Blue Agave, the heart of tequila production. With large-scale cultivation replacing wild harvesting, agave’s genetic uniformity could leave it vulnerable to diseases and pests. By exploring traditional, in-vitro, and experimental reproduction methods and new research into DNA resilience, the tequila industry faces a crucial decision: how to preserve the integrity and future of this iconic plant while maintaining genetic diversity for generations to come.

By: Jesús Hernández, Maestro Tequilero of Altos tequila    

For more than twenty years, I have heard from many sources a genuine concern about the diversity of the Tequilana Weber Blue Agave used in the production of Tequila. 

It all stems from the way new agave fields are established. Because of the scale of tequila production and the fast growth, it was necessary to plant and cultivate agave rather than just harvest the wild agave. It is believed that a lower genetic diversity in the DNA of the agave fields can lead to more susceptibility to disease.

Methods of reproduction

Flower stock 

Agave has two different reproduction methods: One is a sexual method where the mother plant grows a quiote (flower stock), and the flowers that bloom from it are pollinated and scattered by birds and bats; then, they become new plants with a more diverse DNA. 

Vegetative: asexual

The second method is vegetative (asexual), in which the hijuelos (rhizomes) sprout from the roots of a mother plant. The most common and traditional method of growing new fields is harvesting the hijuelos from healthy plants to be used as seeds. These hijuelos have the exact DNA of the mother plant, which is why there is a concern with the DNA diversity. 

In-Vitro Propagation

Various strategies have been developed to address this concern. One of them is in-vitro propagation. In this method, a healthy plant is selected, and the cells are cloned to develop plantlets in a lab. Once these plants reach a certain size, they are placed in a greenhouse environment where they can grow to the size of a grapefruit. 

I have seen some of the fields that used these in-vitro propagated plantlets, and the result was not ideal. Many died from exposure to cold temperatures, and others died from other natural enemies. The survival rate of these plants was much lower. The ones that survived were no better in size and/or sugar content than the agaves planted in the traditional manner.

The Instituto Tecnologico de Tlajomulco near Guadalajara conducted a more radical experiment. It involved irradiating plantlets that were propagated in vitro with gamma rays to modify their DNA. The results are not yet clear, but I find this alternative to be the most dangerous.

Enemies of the Agave: The Fusarium Solani

Research has been conducted on one of the agave plant’s main enemies, the Fusarium solani. This fungus attacks the plant’s root, impeding it from taking moisture and nutrients from the ground. 

It usually appears in fields that are three years or more; the infected plants start changing color to a more pale blue and start to wilt. The disease spreads rapidly from plant to plant, and, once present, it is practically impossible to stop, causing a very high mortality rate, sometimes even a total loss in the field. Even a bigger problem, the disease can spread to nearby fields.

Researchers have noticed that in some severely infected agave fields, some plants survived and looked very healthy, surrounded by wilted plants. They studied the DNA in these surviving plants and conducted experiments to see if they had a natural resistance to the fungus. 

The results were very encouraging; they do seem to have much more resistance. The resulting recommendation was to use these plants to increase the population of plants with DNA with natural resistance. This could be done with in-vitro propagation or by using the “Genetic Reservoir Area” that the CRT (Consejo Regulador del Tequila) keeps in the town of Acatic, Jalisco, to keep and propagate sexually these plants with natural resistance.

In conclusion, the traditional method of reproducing agave plants using rhizomes is not fundamentally wrong. If a careful selection of the hijuelos is made using healthy agave mother plants, then we are mimicking nature in that only the strong survive. Of course, if we feel compelled to help nature, then taking a more conservative approach makes sense. 

Using the Genetic Reservoir Area to grow agave and let them bloom to propagate sexually can help with diversity. It’s even better if we carefully introduce plants that have a natural resistance to enemies. Finally, we can enrich the DNA diversity of this Reservoir by bringing wild agave plants from remote areas such as the ones found in Sonora by the UNAM, the Rhodacantha. This is the closest relative to the Tequilana Weber Blue Agave.