Interpopulation reproductive synchrony of Agave cocui (Agavaceae) in Venezuela

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 one-year 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.     

Physiological activity in persistent bulbils of Agave vilmoriniana (Agavaceae)

Plants of Agave vilmoriniana are unique members of a reproductively diverse genus since they produce prolific numbers of both bulbils and viable seeds. Bulbils were observed to remain attached to the flowering stalk into a second summer, instead of abscising in the year they developed. Hence, a number of hypotheses were tested to establish the physiological basis for their longevity and evaluate their influence upon the plant's reproductive biology. Bulbils produced following anthesis were abundant (>2000 bulbils), large (0.44 g dry mass per individual), and their combined leaf surface area (one side) could exceed 3 m². Thus, the current-year inflorescence may act as a photosynthate source. Second-year, attached bulbils are healthy-looking, even after leaves of the parent plant have senesced, since maternal roots continue to absorb rain water. Rehydrated 2nd-yr bulbils resume Crassulacean acid metabolism, sometimes demonstrating net daytime tissue acidification. Water conservation by bulbils is very efficient, exhibiting very low cuticular conductances (0.016-0.0035 mm/s). Bulbils detach over all climatic seasons after having formed >3 and >18 root primordia in their 1st and 2nd year, respectively. About one-third of bulbils are capable of forming roots after a 1-yr storage at 35°C, when their water contents averaged 37%. Irrigated bulbils produce water-absorbing roots within 2 d, with de novo chlorophyll synthesis and nocturnal acidification commencing within 4 d. Two bulbils were observed to root and become established in shaded microhabitats during this 2-yr study of 29 plants.     

Genetic differentiation in the Agave deserti (Agavaceae) complex of the Sonoran desert

The Agave deserti complex, comprising A. deserti, A. cerulata and A. subsimplex, represents a group of species and subspecies with a near allopatric distribution and clear differences in morphology. Genetic differentiation and taxonomic status with respect to spatial distribution of 14 populations of the complex were analyzed in an effort to understand the evolution and speciation process within the genus. Allelic frequencies, levels of genetic variation, expected heterozygosity (H(S)), proportion of polymorphic loci (P), and genetic differentiation (theta and Nei's genetic distance) were estimated using 41 putative RAPD loci. All three species show high levels of genetic variation (H(S)=0.12-0.29, P=63.4-95.1), and low genetic differentiation between populations and species (theta populations=0.14+/-0.02 (SE); G(st)=0.11+/-0.02). Accordingly, gene flow among populations was estimated as high by three different methods (N(m)=2.91-6.14). Nei's genetic distances between the three species were low compared to the values obtained from other Agavaceae, and there was no clear correlation with taxonomic divisions. In a UPGMA analysis, A. subsimplex and A. cerulata formed exclusive monospecific clusters, whereas the A. deserti populations appear in more than one cluster together with other species. The results were consistent with a pattern of genetic isolation by distance.     

Reproductive ecology of five sympatric Agave Littaea (Agavaceae) species in central Mexico

We studied a community of Agave species that coexist in the Metztitlán Canyon in Central Mexico. During 2001, 2002, and 2003, we analyzed floral traits and rosette allometry in five species belonging to the subgenus Littaea: A. celsii albicans, A. xylonacantha, A. difformis, A. striata, and Agave sp.; and observed floral visitors for each species. We report the first evidence of bat visitation in the subgenus Littaea and find that bats (Leptonycteris curasoae, Choeronycteris mexicana, and Glossophaga sp.) are the primary pollinators in four species. Honeybees, hummingbirds, bumblebees and hawkmoths were also common visitors. We propose that the presence of diurnal pollinators may increase the reproductive success of the plant when offering pollinator services additional to the coadapted pollinator. We also found evidence of selection pressures toward semelparity because pollinators are selecting for taller inflorescences in three of the five species. There is phenological complementarity in this community because the flowering periods of the five species span the entire year, although there are some periods when pairs of species overlap. Additionally, we found evidence for character displacement in rosette sizes and separation of spatial and temporal resource use in pollinator composition among species.     

Post-harvest growth of Lechuguilla (Agave lecheguilla torr., Agavaceae) in Northeastern Mexico

Extraction of lechuguilla fiber (Agave lecheguilla) is often the only source of income for some rural inhabitants in arid zones of Mexico. A model for biomass estimation of lechuguilla by nondestructive techniques was developed and then applied to evaluate whether traditional harvesting had an effect on (1) biomass production of the bud (part of the plant traditionally collected to obtain fiber) and (2) plant density. Six months after harvesting, biomass production was higher for buds of harvested plants than for buds of unharvested plants, but there were no differences 1 year after harvesting. Number of new plants was not affected by harvesting. Hence it appears that at least in the short term the common practice for extracting lechuguilla fiber does not affect population density, but significantly increases growth of central buds.     

Genetic diversity of the endangered endemic Agave victoriae-reginae (Agavaceae) in the Chihuahuan Desert

Long-lived perennials are a species-rich, ecologically important component of the North American deserts, yet we know little about their genetic structure, information important for their conservation. Agave victoriae-reginae is an endemic of the Chihuahuan Desert of northern Mexico that is endangered by collection for the ornamental trade. We examined levels and patterns of variation at ten polymorphic allozyme loci in ten populations representing the range of the species. Levels of genetic variation (mean H_e= 0.335) and differentiation (mean F_ST = 0.236) were high. Phenetic clustering suggested the existence of at least three distinct groups of populations. If this pattern of variation is representative of other long-lived desert perennials, it may explain the species richness of this group and will pose a real challenge to gene conservation efforts.     

Agave rzedowskiana, a new species in subgenus Littaea (Agavaceae) from western Mexico

Agave rzedowskiana is described and illustrated from the states of Sinaloa and Jalisco, Mexico. This species is a member of subgenusLittaea (Tagliabue) Baker “groupStriatae” of Baker. It is compared withA. petrophila García-Mend. & E. Martínez andA. dasylirioides Jacobi & Bouché.

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Resumen  Se describe e ilustraAgave rzedowskiana de los estados de Sinaloa y Jalisco, México. La especie pertenece al subgéneroLittaea (Tagliabue) Baker “Grupo Striatae” de Baker. Se le compara conA. petrophila García-Mend. & E. Martínez yA. dasylirioides Jacobi & Bouché.

     

Reproductive biology of henequen (Agave fourcroydes) and its wild ancestor Agave Angustifolia (Agavaceae). i. Gametophyte development

The pathways of micro- and megagametophyte development in Agave fourcroydes (henequén) and A. angustifolia were studied. We used histology and light microscopy to observe anther ontogeny and ovary differentiation in relation to flower bud size. Both species have the same sexual reproductive strategies and gametophyte development that may be divided into three phases: (1) premeiotic, which includes the establishment of the megaspore mother cell and the pollen mother cell; (2) meiotic, the formation of mature microspores and functional megaspores; (3) postmeiotic, which encompasses the development of mature pollen grains and the formation of the embryo sac. A successive type microsporogenesis was found in both species with formation of T-shaped tetrads and binuclear pollen grains. In vitro germination tests revealed very low pollen fertility. The female gametophyte is formed from two micropylar megaspore cells after the first meiotic division (bisporic type). Male and female gametogenesis occur asynchronously with microsporogenesis finishing before macrosporogenesis. The results so far show that the formation of male and female gametophytes in henequén is affected at different stages and that these alterations might be responsible for the low fertility shown by this species.     

Genetic consequences of pre-Columbian cultivation for Agave murpheyi and A. delamateri (Agavaceae)

Pre-Columbian farmers cultivated several species of agave in central Arizona from ca. A.D. 600-1350. Because of the longevity and primarily asexual reproduction of these species, relict agave clones remain in the landscape and provide insights into pre-Columbian agricultural practices. We analyzed variation in allozyme allele frequencies to infer genetic effects of prehistoric cultivation on Agave murpheyi and A. delamateri, specifically to estimate genetic diversity and structure, to determine whether cultivated populations descended from a single clone, and to examine regional-scale genetic variation. Agave murpheyi maintained more genetic diversity at the species and population levels than A. delamateri, and A. murpheyi populations typically included more multilocus genotypes. Relict plants from prehistoric fields reflect a more complex history than descent from a single clone; A. murpheyi populations may have included more diversity initially because bulbils (produced routinely in A. murpheyi but not A. delamateri) and possibly seed would have facilitated transport of genetically diverse planting stock. Genetic variation in both cultigens was lower than in most contemporary commercial crops but similar to that observed in modern traditional agricultural systems.     

A few varietal combinations in Californian Keckiella and Penstemon (Scrophulariaceae)

Combinations are made forKeckiella antirrhinoides var.microphylla, K. rothrockii var.jacintensis, K. ternata var.septentrionalis, Penstemon fruticiformis var.amargosae, P. grinnellii var.scrophularioides, P. heterodoxus var.cephalophorus, P. heterodoxus var.shastensis, andP. newberryi var.berryi.     

Propagation mechanisms in Agave macroacantha (Agavaceae), a tropical arid-land succulent rosette

Agave macroacantha can sexually reproduce by seeds and propagate vegetatively by aerial bulbils and ground-level basal shoots and rhizomes. It forms compact patches apparently generated by the multiplication of ground-level offshoots. We experimentally evaluated the establishment and survival of bulbils and seedlings of A. macroacantha in the Tehuacán Valley, Mexico, between 1991 and 1994 and studied comparatively the effectiveness of sexual reproduction against vegetative propagation.Seedlings showed low survival rates. Cohorts placed outside nurse plants died in less than 1 yr, while 1-10% of cohorts under nurse plants survived for more than 2 yr. Herbivores negatively affected seedling survival in non-nursed plots. In rainy years, survival rates increased. Bulbils showed higher survival rates than seedlings.The excavation of rosettes showed that most are derived from vegetative shoots, as indicated by remains of rhizomes in their base. Most rosettes had ground-level vegetative offspring totaling almost three shoots per rosette.In A. macroacantha, the establishment of seedlings and bulbils is a rare event that possibly only occurs under nurse plants in rainy years, while ground-level cloning is highly effective as a propagation mechanism. These results are consistent with the aggregated spatial pattern of the species.     

Two new Agave species (Agavaceae) from central Arizona and their putative pre-Columbian domesticated origins

Recent fieldwork in central Arizona resulted in the discovery of two agaves that display low seed set, reproduce mainly by vegetative means, have restricted distributions, and cannot be readily assigned to any existing species. These agaves are closely associated with archaeological structures and features and can be found growing with other previously described pre-Columbian Agave domesticates. Herein we describe Agave verdensis and A. yavapaiensis, two species that can be placed within Gentry’s informal Ditepalae Agave group, and propose that they are clonal relict domesticates. The two species have affinities with A. chrysantha, A. shrevei, and A. delamateri, the latter also a central Arizona pre-Columbian domesticate. We provide a key to distinguish these species from other agaves in central Arizona and adjacent northern Mexico with which they may be confused. The discovery of these two new species brings the total number of putative Arizona Agave domesticates to five species.     

Agave turneri (Agavaceae), a new species from northeastern Baja California, Mexico

Agave turneri, a new species of Agave from the Sierras Cucapá and El Mayor in northeastern Baja California, Mexico, is a medium-sized species that does not produce offsets, has a relatively short and narrow panicle, and has a distinctive flower structure. The closest relatives to this new species are Agave moranii, which occurs approximately 200 km to the south of the type locality, and A. deserti var. simplex, which occurs in Arizona and California. This new species is a narrow endemic restricted to specific granodiorite and tonalite habitats in a hyperarid environment. Agave turneri appears to be a critically endangered owing to its habitat preference for specific types of granite in the Sierra Cucapá, threats due to prolonged drought and global change, and its close proximity to the Mexicali metropolitan area.     

Isozymatic variation and phylogenetic relationships between henequen (Agave fourcroydes) and its wild ancestor A. angustifolia (Agavaceae)

Isozymatic variation and phylogenetic relationships among extant henequén (Agave fourcroydes) germplasm and wild populations of its ancestor A. angustifolia in the Yucatan Peninsula in Mexico were analyzed. Analysis of three isozyme systems using starch gel electrophoresis indicated that while A. angustifolia populations have relatively high levels of variation, within each henequén cultivar all individuals were identical. This result corresponds to previous ethnobotanical and morphological analyses, which indicated severe loss of genetic variation of this domesticated plant as a consequence of the promotion by means of asexual propagation of only one cultivar since the middle of the last century. The three extant cultivars of henequén were distinct from each other. Two of them, Sac Ki (SK) and Yaax Ki (YK), could be matched within the progenitor, but Kitam Ki (KK) has a MDH electrophenotype not found in any of the plants growing inside the Yucatan Peninsula, but found in some A. angustifolia plants growing in the Mexican states of Oaxaca and Veracruz. A parsimony analysis of the morphological data indicated two lineages: that of SK and YK, cultivated cordage plants selected for stronger and longer fibers, whose sister group is the Tropical subdeciduous forest ecotype (SF), and that of all the other wild populations, which also included KK, the cultivated textile plants selected for finer fibers and nearly extinct in Yucatan. These results support the hypothesis of the yucatecan origin of SK and YK from the SF ecotype, as well as the hypothesis of a recent introduction of KK to the Yucatan Peninsula in a domestication trend that probably included also Chelem White (its cultivation being abandoned later).     

A taxonomic revision of the genus Agave (Agavaceae) in the Lesser Antilles, with an ethnobotanical hypothesis

The genusAgave (Agavaceae) is revised taxonomically for the Lesser Antilles. All 12 previously recognized species are placed into synonymy underAgave karatto Miller. A neotype is selected for the nameAgave karatto, and lectotypes are designated forA. barbadensis Trel.,A. medioxima Trel.,A. obducta Trel.,A. vangrolae Trel., andA. ventum-versa Trel. Specimens are cited for most of the Lesser Antillean islands. That the Caribbean agaves are similar to the MexicanAgave nayaritensis Gentry is supported. The hypothesis that the pattern of partial sterility, clonality, and minimal morphological differentiation of the Lesser Antillean agaves is related to prehistoric human activity is developed based on similar patterns among mainland agaves and historical information. Uses for the archaeological “Barbados shell tool” may have included decorticating agave leaves for fiber extraction.     

The comparative leaf anatomy of Agave, Beschorneria, Doryanthes and Furcraea species (Agavaceae: Agaveae)

The leaf anatomy is compared of 35 ppecies and one variety of Agave , three species of Furcraea , one species of Beschorneria and one species of Doryanrhes , four genera assigned to the tribe Agaveae by Hutchinson in his classification of the family Agavaceae. The genera can be readily differentiated by leaf anatomy. There are close similarities between Agave, Beschorneria and Furcraea , but Doryanthes differs widely from these genera. Sufficient anatomical differences exist to differentiate the Agave species examined.     

In vitro induction of a trisomic of Agave tequilana Weber var. Azul (Agavaceae) by para-fluorophenylalanine treatment

The effect of para-fluorophenylalanine (PFP) on the production of trisomic plants of Agave tequilana Weber var. Azul produced through somatic embryogenesis was investigated. Normal diploid plants with 2n = 2x = 60 were obtained in the control treatment and with 4 mg L⁻¹ PFP exposure, while use of 8 and 12 mg L⁻¹ PFP led to production of trisomics with 2n = 2x = 61. Normal diploid plants showed a bimodal karyotype with five pairs of large chromosomes and 25 pairs of small chromosomes. Trisomic plants also had a bimodal karyotype with a group of three chromosomes in position five of the chromosome set. More than 13 homologous chromosome pairs exhibited structural changes. Differences in chromosome arm ratio (long arm/short arm) were also found in eight chromosome pairs; all these aberrations in the chromosome complement of trisomic plants were probably caused by inversions, deletions, and/or duplications produced by high concentrations of PFP. The gross chromosome structural changes and the presence of a single extra chromosome could have been induced by the effect of PFP on the mitotic spindle by inducing nondisjunction of sister chromatids, resulting in hyperploids (2n + x) and hypoploids (2n − x). Flow cytometric analysis of nuclear DNA content was performed using nuclei isolated from young leaves of normal and trisomic plants. The 2C DNA content of 8.635 pg (1Cx = 4,223 Mbp of trisomic plants was different (p < 0.001) than that of normal plants (2C DNA = 8.389 pg (1Cx = 4,102 Mbp). The difference in genome size was correlated with the large structural changes in the trisomic plant genomes.