Conservation genomics of Agave tequilana Weber var. azul: low genetic differentiation and heterozygote excess in the tequila agave from Jalisco, Mexico

Lessons from the history of Agave: ecological and cultural context for valuation of CAM

BACKGROUND AND SCOPE

Crassulacean acid metabolism (CAM) is an intriguing physiological adaptation in plants that are widespread throughout many ecosystems. Despite the relatively recent mechanistic understanding of CAM in plant physiology, evidence from historical records suggests that ancient cultures in the Americas also recognized the value of CAM plants. Agave species, in particular, have a rich cultural legacy that provides a foundation for commercially valued products. Here, we review that legacy and potential relationships between ancient values and the needs of modern-day climate adaptation strategies.

CONCLUSIONS

There are many products that can be produced from Agave species, including food, sugar, fibre and medicines. Traditional knowledge about agricultural management and preparation of plant products can be combined with new ecophysiological knowledge and agronomic techniques to develop these resources in the borderland region of the southwestern USA and Mexico. Historical records of pre-Columbian practices in the Sonoran desert and remnants of centuries-old agriculture in Baja California and Sonora demonstrate the climate resilience of Agave agriculture. Commercial growth of both tequila and bacanora indicates the potential for large-scale production today, but also underscores the importance of adopting regenerative agricultural practices to accomplish environmentally sustainable production. Recent international recognition of the Appellation of Origin for several Agave species produced for spirits in Mexico might provide opportunities for agricultural diversification. In contrast, fibre is currently produced from several Agave species on many continents. Projections of growth with future climate change suggest that Agave spp. will be viable alternatives for commodity crops that suffer declines during drought and increased temperatures. Historical cultivation of Agave affirms that these CAM plants can supply sugar, soft and hard fibres, medicines and food supplements.

Genomic analysis unveils reduced genetic variability but increased proportion of heterozygotic genotypes of the intensively managed mezcal agave, Agave angustifolia

PREMISE

The central Oaxaca Basin has a century-long history of agave cultivation and is hypothesized to be the region of origin of other cultivated crops. Widely cultivated for mezcal production, the perennial crop known as "espadín" is putatively derived from wild Agave angustifolia. Nevertheless, little is known about its genetic relationship to the wild A. angustifolia or how the decades-long clonal propagation has affected its genetics.

METHODS

Using restriction-site-associated DNA sequencing and over 8000 single-nucleotide polymorphisms, we studied aspects of the population genomics of wild and cultivated A. angustifolia in Puebla and Oaxaca, Mexico. We assessed patterns of genetic diversity, inbreeding, distribution of genetic variation, and differentiation among and within wild populations and plantations.

RESULTS

Genetic differentiation between wild and cultivated plants was strong, and both gene pools harbored multiple unique alleles. Nevertheless, we found several cultivated individuals with high genetic affinity with wild samples. Higher heterozygosity was observed in the cultivated individuals, while in total, they harbored considerably fewer alleles and presented higher linkage disequilibrium compared to the wild plants. Independently of geographic distance among sampled plantations, the genetic relatedness of the cultivated plants was high, suggesting a common origin and prevalent role of clonal propagation.

CONCLUSIONS

The considerable heterozygosity found in espadín is contained within a network of highly related individuals, displaying high linkage disequilibrium generated by decades of clonal propagation and possibly by the accumulation of somatic mutations. Wild A. angustifolia, on the other hand, represents a significant genetic diversity reservoir that should be carefully studied and conserved.