Guadalupe Malda

The present study establishes an efficient protocol for in vitro propagation from longitudinal sections of seedlings of Beaucarnea purpusii, a threatened and highly appreciated ornamental species. The effect of three cytokinins: N 6-benzyladenine (BA), kinetin (Kin), and thidiazuron, 1-phenyl-3-(1,2,3-thiadiazol-5-yl)urea (TDZ), in semi-solid media and three different concentrations, as well as the effect of BA and TDZ pulses at higher concentrations in liquid culture medium, were investigated. Adventitious shoot formation by direct organogenesis was observed from all treatments. Additionally, adventitious shoot formation was recorded from the leaves of the new shoots; this particular response was exclusive to treatments supplemented with TDZ. In the experiment using semisolid culture media, the highest means of shoots per explant were obtained from treatments containing TDZ, particularly at a concentration of 0.45 mM (25.8 shoots per explant). For the pulses experiment, the liquid culture media supplemented with TDZ at 22.35 mM for 24 hours and 136.21 mM for 96 hours, induced a mean of 3.9 and 3.3 shoots per explant, respectively. Subculturing individual shoots on MS and half-strength MS (1/2MS) media, both supplemented with activated charcoal at 1 g · L L1 , induced rooting in 85% to 95% of shoots. A survival rate of 100% under greenhouse conditions was achieved. The results of this study provide an efficient alternative for mass propagation of B. purpusii and may also contribute to the conservation and sustainable use of this valuable natural resource.

Having an aesthetic form is one of the desirable aspects of trees used to create or reforest urban green areas, which is often achieved by procedures that require a great effort. The understanding of factors affecting the architecture of plants in natural conditions may be useful to promote a desirable shape during the growth process. Under the hypothesis that trees in high luminosity conditions have a more aesthetical growth, in this study we explore the relationship between plant shape and photosynthetically active radiation (PAR) in Bursera fagaroides, a characteristic species of the tropical dry forest and xerophytic shrub-lands useful for urban green areas in semiarid environments. To evaluate trees shape we calculate a symmetry index (I S) by using two diameters of the crown, perpendicular to each other, and the total height. Measurements were made over three periods (before, during and after the growth period); and PAR was also measured for each tree. Linear regressions were used to analyze the relationship between the symmetry of trees and PAR received during the growth period. The post-growth symmetry of trees showed a positive relationship with the PAR received by trees during the growth period, suggesting that PAR effects can be harnessed to develop post-germination strategies for the production of trees with a more aesthetical growth in the studied species. Effect of PAR on the shape of plants may represent a practical option to promote aesthetical growth of trees and shrubs with importance for creation and restoration of urban green areas.

The proportion of viable seeds and loss of viability due to age, as well as the conditions which promote germination in Taxodium mucronatum from two different cohorts (2000 and 2002), were determined in the State of Querétaro, México. Seeds from the 2002 cohort had a viability of over 50%, whereas those of 2000 presented a viability of 30% or less.

Unlike C-3 plants, cacti possess a crassulacean acid metabolism (CAM) physiology that can alter the pattern of carbon uptake and affect plant growth under artificial environmental conditions, especially in tissue culture. In vitro-derived plantlets of Coryphantha minima grew 7-fold larger than plants cultured under similar ex vitro conditions. Growth regulators incorporated into the culture media during shoot proliferation stage of micropropagation had a strong influence on this increased growth. Other important factors that contributed to increased growth under in vitro conditions were high relative humidity and sugar in the culture medium. An analysis of gas exchange and daily fluctuations of malic acid levels revealed an increase in net photosynthetic rate, in terms of carbon assimilation, by in vitro plants compared with that of ex vitro plants. This stimulated photosynthesis in the presence of an external carbon source was unexpected but apparently true for cacti exhibiting CAM physiology. Unlike CAM plants grown in ex vitro conditions, net CO2 uptake by in vitro-cultured cacti occurred continuously in the light as well as the dark. Once regenerated, cacti were transferred to ex vitro conditions where the normal CAM pathway resumed with a concomitant reduction in growth and CO2 uptake. These results showed that growth of cacti can be considerably accelerated by in vitro culture.

One of the two species from the genus Lophophora is the false peyote Lophophora diffusa, an endemic cactus species of the xerophytic shrubland at Querétaro, México, considered threatened from illegal extraction due to its hallucinogenic and medicinal properties. We analyzed the spatial distribution of L. diffusa and its association with the locally dominant shrub species with the system SADIE (Spatial Analysis by Distance IndicEs). We also studied the principal microclimatic factors (light, temperature, and humidity) beneath the canopy of the possible nurse plant species. The use of SADIE is a new approach to study the mechanisms of spatial distribution. Lophophora diffusa and the shrub species presented an aggregated distribution with patches and gaps, as indicated by the values of Ia= 4.179 for L. diffusa and Ia= 1.660 for the vegetation. Lophophora diffusa was positively associated with the arboreal vegetation, particularly with Larrea tridentata and Acacia sororia, but was negatively associated with Celtis pallida and Myrtillocactus geometrizans. Microclimate evaluation indicated that C. pallida canopy significantly reduced radiation and temperature compared to the other species (L. tridentata, A.sororia y P. laevigata). We had expected L. diffusa to exhibit a positive spatial association with C. pallida; however, the reduction in light availability apparently limited seedling establishment of L. diffusa.Una de las dos especies del género Lophophora es el falso peyote, Lophophora diffusa, cactácea endémica al matorral xerófilo de Querétaro, México y considerada amenazada debido a su extracción ilegal, pues se le atribuyen los efectos alucinógenos y medicinales del peyote, L. williamsii. Utilizando el sistema de Análisis Espacial por Índices de Distancia, SADIE (por sus siglas en inglés), analizamos la distribución espacial de L. diffusa y determinamos si había asociación con alguna especie arbustiva, caracterizando además las condiciones microambientales (luz, temperatura y humedad) bajo su dosel. El uso de SADIE constituye una nueva aproximación al estudio de los mecanismos de distribución espacial. Los índices de agregación obtenidos indican que L. diffusa, lo mismo que la vegetación, presenta una distribución agregada en parches y claros, siendo los valores de Ia= 4.179 para L. diffusa y Ia= 1.660 para la vegetación. Se detectó asociación espacial de L. diffusa con la vegetación arbustiva, particularmente la relación fue significativa con Larrea tridentata y Acacia sororia, siendo las especies más abundantes, en contraste se encontró una disociación con Celtis pallida, y Myrtillocactus geometrizans. La evaluación de los factores microambientales indica que las condiciones bajo el dosel de L. tridentata, A. sororia y P. laevigata son similares, mientras que el microambiente debajo de C. pallida es más oscuro. Bajo estas circunstancias, se esperaría que L. diffusa estuviera más asociada a dicha especie, pero la reducción de luz aparentemente limita el establecimiento de las plántulas de L. diffusa.