Mexico is a megadiverse country, but less than 54 % of its original vegetation still remains. In particular Mexican deserts and arid and semiarid ecosystems harbor a large number of endemic taxa, and the genus Agave is an outstanding example. Agave is one of the largest genera of the Mexican flora, including a total estimated number of 200 species, 74 % of them endemic to the country. Agave is also one of the Mexican plant genera with more population genetic studies. We describe here studies in 22 Agave species using different genetic markers. For the genus we found on average a high level of genetic variation, H
 s
  = 0.19, and a low genetic differentiation, F
 st
  = 0.15. We identify some species that should be subject to special conservation genetic efforts, in particular the endangered A. victoriae-reginae and both wild populations and landraces of A. angustifolia, including the cultivated A. tequilana.

From Isozymes to Genomics: Population Genetics and Conservation of Agave in México

Genetic diversity, conservation and sustainable use of wild Agave cupreata and Agave potatorum extracted for mezcal production in Mexico

Nuevo catálago de la flora vascular de Venezuela

Domestication is a continuous evolutionary process guided by humans. This process leads to divergence in characteristics such as behaviour, morphology or genetics, between wild and managed populations. Agaves have been important resources for Mesoamerican peoples since prehistory. Some species are domesticated and others vary in degree of domestication. Agave inaequidens Koch is used in central Mexico to produce mescal, and a management gra- dient from gathered wild and silvicultural populations, as well as cultivated plantations, has been documented. Significant morphological differences were reported among wild and managed populations, and a high phenotypic variation in cultivated populations composed of plants from different populations. We evaluated levels of genetic diversity and structure associated with management, hypothesizing that high morphological variation would be accompanied by high genetic diversity in populations with high gene flow and low genetic structure among managed and unmanaged populations. Wild, silvicultural and cultivated populations were studied, collecting tissue of 19-30 plants per population. Through 10 nuclear microsatellite loci, we compared population genetic parameters. We analysed partition of variation associated with management categories to estimate gene flow among populations. Agave inaequidens exhibits high levels of genetic diversity (He ¼ 0.707) and moderate genetic structure (FST ¼ 0.112). No differences were found in levels of genetic diversity among wild (He ¼ 0.704), silviculturally managed (He ¼ 0.733) and cultivated (He ¼ 0.698) popula- tions. Bayesian analysis indicated that five genetic clusters best fit the data, with genetic groups corresponding to habi- tats where populations grow rather than to management. Migration rates ranged from zero between two populations to markedly high among others (M ¼ 0.73-35.25). Natural mechanisms of gene flow and the dynamic management of agave propagules among populations favour gene flow and the maintenance of high levels of variation within all popu- lations. The slight differentiation associated with management indicates that domestication is in an incipient stage.

/pdf/genetic-structure-of-coexisting-wild-and-managed-agave-2mw4xophyo.pdf

Genetic structure of coexisting wild and managed agave populations: implications for the evolution of plants under domestication.

Agave potatorum is a wild endemic species of Mexico. Its stems are used for mescal production, which cancels sexual reproduction. Agaves extraction from forests decreases their reproductive success and demographic performance. We evaluated patterns of genetic diversity and structure of wild populations under and without extraction in order to identify effects of its use and actions required for conserving genetic variation. This study was conducted with seven SSR markers in 12 populations representing the entire distribution area of the species. Standard parameters of genetic diversity, differentiation, structure and genetic similarity of populations were calculated and analyzed. The populations studied showed intermediate to high genetic diversity (H
 e
  = 0.36–0.64), compared with other Agave species so far studied. The wild category was the most diverse (H
 T
  = 0.87), but without significant differences with respect to populations under extraction (H
 T
  = 0.72), and two germplasm banks sampled (H
 T
  = 0.69). High structure among populations (Φ
 PR
  = 0.38) and inbreeding levels (F
 IS
  = 0.26, F
 IT
  = 0.55) were identified; a 3 % of genetic diversity being distributed among management status where germplasm banks represent a genetic pool with incipient divergence from the other categories. Bayesian analysis indicated two genetic groups. Our study suggests slight effects of management on genetic diversity of A. potatorum, apparently related to alterations of reproductive biology and pollination patterns.

Effects of traditional management for mescal production on the diversity and genetic structure of Agave potatorum (Asparagaceae) in central Mexico

The Agave genus embraces many species with outstanding ecological and economic importance in the arid regions of the Americas. Even though this genus covers a broad geographic distribution, our knowledge on the population genetics of species is concentrated in taxa located in North America. Recently, it has been demonstrated that plant domestication decreases levels of genetic diversity in managed populations and increases population structure with respect to wild populations. We examined levels of allozyme diversity (N = 17 loci) and population structure of Agave cocui, the species at the southern limit of distribution of the genus. We sampled 7 wild populations (N = 30-35 individuals per population) representative of the geographic distribution of the species in Venezuela. Among the agaves studied, A. cocui has some of the lowest estimates of genetic diversity (H(e)[species] = 0.059, H(e)[population] = 0.054) reported until present. We propose that this condition is probably linked to the recent origin of this species in arid and semiarid regions of Colombia and Venezuela, probably through one or a few founder events. The lowest estimates of genetic diversity were associated with small populations in very restricted arid patches; but also with overexploitation of rosettes for production of fermented drinks and fibers. Santa Cruz de Pecaya, one of the 2 centers of economic use of agaves in northwestern Venezuela presented one of the lowest values of genetic variability, a sign suggesting that human impact represents a significant threat to the available genetic pool that this species possesses in the region.

/pdf/population-genetics-of-agave-cocui-evidence-for-low-genetic-50es6q4eds.pdf

Population Genetics of Agave cocui: Evidence for Low Genetic Diversity at the Southern Geographic Limit of Genus Agave

Agave cocui (Agavaceae) is a species with broad distribution in arid and semiarid areas of Venezuela and Colombia. Despite of its ecological importance as a source of food for wildlife, and its economic value for production of a spirit drink, studies on the reproductive ecology of the species are relatively rare. In this study, we conducted a oneyear evaluation of the flowering and fruiting phenology of A. cocui in the eight representative localities of the species? distribution in Venezuela. Within each study site, we chose an area with a minimum of 50 reproductive individuals and followed their reproductive phenophases with the help of binoculars, using six qualitative cathegories (emerging reproductive stalk, flowers, inmature fruits, mature fruits, bulbils and dry stalk) every two months. Emergence of the reproductive stalk in most of the examined populations began in September (rainy season), although this event delayed two months in a few populations. We detected significant negative correlations between precipitation and the percentage of flowering occurrence in four of the eight populations. Floral resources are available for flower visitors during approximately five months of the year (January-May). In most populations production of flowers initiated in January (dry season), and for Western Venezuela and Andean regions, the flowering main peak occurred in January. Localities from the Central and Eastern Coast exhibited the flowering peak in March, showing a delay of approximately two months with respect to other populations. Beginning of fruit set varied among localities from January to May; however, peak production of mature fruits concentrated in May, and fruit occurrence varied broadly between 5.2 and 85%. Bulbil production was detected in all populations and varied greatly among them (maximum percentage per population: 26.19-92.10%). High flowering synchronicity (Phenophase Overlapping Index: 0.756 and 0.999) was observed among all populations monitored in Western Venezuela, including the Andean localities. This condition might facilitate the existence of a nectar corridor from the Western Coast and nearby islands, to the Andean arid patches, which could be potentially used by nectar-feeding bats and birds dependent on agave flowers during part of the year.

/pdf/sincronia-reproductiva-interpoblacional-de-agave-cocui-3x5sf0ydvq.pdf

Carmen J. Figueredo

Papers

Population Genetics of Agave cocui: Evidence for Low Genetic Diversity at the Southern Geographic Limit of Genus Agave

Sincronía reproductiva interpoblacional de Agave cocui (Agavaceae) en Venezuela