Browsing by Author "Contreras, Samuel"

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    Characterisation of seed dormancy of 12 Chilean species of Nolana (Solanaceae) from the coastal Atacama Desert
    (CAMBRIDGE UNIV PRESS, 2021) Hepp, Josefina; Gomez, Miguel; Leon Lobos, Pedro; Montenegro, Gloria; Vilalobos, Luis; Contreras, Samuel
    The genus Nolana (Solanaceae) comprises numerous species endemic to the coastal Atacama Desert of Chile and Peru of high ornamental potential and conservation value. The environments in which these species have evolved and are present today correspond to particular conditions in the midst of a hyper-arid habitat, so the study of their germination requirements and characterisation of seed dormancy becomes important in terms of conservation but also for ecological and evolutionary purposes. Different treatments were performed on mericarps of 12 species of Nolana: control (intact seeds imbibed in distilled water), scarification in funicular plug and distilled water and scarification in funicular plug and addition of GA(3) (500 ppm); their permeability to water was also tested. It was determined that the species did not present physical dormancy, as had been previously reported, but rather physiological dormancy (PD). Germination results after treatments were not homogeneous among all 12 species, indicating differences in their dormancy levels. Also, the important role of the endosperm in the prevention of germination for the studied Nolana species was highlighted. Regarding the relationship between the level of PD (expressed as the percentage of germination for the most successful treatment) and the latitudinal distribution of the species or their phylogenetic closeness, it was determined that, for the studied species, their proximity in terms of clades was more relevant than their latitudinal distribution.
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    Identificación de especies de micobacterias mediante espectrometría de masas (MALDI-TOF)
    (2020) Contreras, Samuel; Rodriguez, David; Vera, Francisco; Balcells Marty, María Elvira; Celis, Luis; Legarraga Raddatz, Paulette; Carlos Roman, Juan; García Cañete, Patricia
    Introducción: Las enfermedades producidas por micobacterias son de gran importancia clínica y epidemiológica presentando el complejo Mycobacterium tuberculosis (MTBc) una morbi-mortalidad mayor que la producida por micobacterias no tuberculosas (MNTB). La identificación tradicional está basada en sus características fenotípicas mediante procesos laboriosos e incapaces en algunos casos de distinguir entre especies. Actualmente, la mayoría de las técnicas utilizadas se basan en métodos moleculares que tienen alta veracidad, pero son complejas y de alto costo. La espectrometría de masas con desorción/ionización láser asistida por una matriz asociada a tiempo de vuelo (MALDI-TOF MS) se basa en la comparación del espectro proteico producido con respecto al de una base de datos de referencia. Objetivo: Evaluar el rendimiento de MALDI-TOF MS en la identificación de micobacterias comparado con métodos moleculares: Material y Métodos: Se analizaron 28 aislados de nueve especies distintas mediante MALDI-TOF MS. Resultados: Se identificó correctamente 78,5% de las aislados (22/28), concordante en 100% (9/9) de MNTB de crecimiento rápido, 60% (9/15) en las MNTB de crecimiento lento y 100% (4/4) de MTBc. Todas las especies no identificadas (6/6) pertenecen al complejo M. avium/intracellulare. Conclusión: MALDI-TOD MS es una metodología rápida, fácil y de bajo costo, con adecuada veracidad respecto a los métodos moleculares.
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    Maternal light environment during seed development affects lettuce seed weight, germinability, and storability
    (AMER SOC HORTICULTURAL SCIENCE, 2008) Contreras, Samuel; Bennett, Mark A.; Metzger, James D.; Tay, David
    Seed germinability and storability are important aspects of seed quality determined by the genotype and environment of seed development. Lettuce (Lactuca sativa L.) is produced commercially in most temperate and subtropical areas of the world. The objective of this study was to determine how photoperiod and light quality of the mother plant environment affects lettuce seed quality. Seeds of cv. Tango were produced in growth chambers under one of two treatments: a) short day (SD), consisting of 8 hours of fluorescent light (approximate to 310 mu mol.m(-2)-s(-1)) plus 16 hours of darkness daily, and b) long day (LD), consisting of 4 hours of incandescent light (approximate to 21 mu mol.m(-2.)s(-1)), 8 hours of fluorescent light, 4 hours of incandescent light, and 8 hours of darkness daily. The red to far-red ratio was approximate to 6.8 and 1.0 for the fluorescent and incandescent light, respectively. In both treatments, the temperature was 23 degrees C. The LD treatment produced significantly heavier seeds; however, germination at optimal conditions (20 degrees C-light) was similar for both treatments. Germinability (percentage and rates) at suboptimal conditions (30 degrees C, 20 degrees C with different external ABA concentrations, negative osmotic potentials, or dark) was higher for seeds produced under the LD treatment. On the other hand, seeds produced under the LD treatment presented better storability (evaluated by the accelerated aging test and standard germination after storage at 30 degrees C and 74% 1114). The critical period for light environment effects was also studied. Seed weight patterns were determined early in seed development, during the first 6 days after flowering. Conversely, light environment effects on seed germinability and storability were determined at the end of seed development, after physiological maturity, which occurred by 11 days after flowering. These results show that lettuce seed germinability and storability may he modified by management of light conditions during seed production and provide useful information for seed producers, seed companies, and seed conservation institutions.
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    Red to Far-red Ratio During Seed Development Affects Lettuce Seed Germinability and Longevity
    (AMER SOC HORTICULTURAL SCIENCE, 2009) Contreras, Samuel; Bennett, Mark A.; Metzger, James D.; Tay, David; Nerson, Haim
    Thermoinhibition and photosensitivity are two characteristics of lettuce seed that frequently affect its stand. The main objective of this study was to evaluate the hypothesis that lettuce seed germinability and longevity are affected by the red to far-red light ratio (R:FR) under which seeds maturate. 'Tango' lettuce seeds were produced in growth chambers under one of two treatments: 1) red-rich light (11 treatment) and 2) far-red-rich light (FR treatment). For both treatments, the percentage of normal seedlings germinated at 20 degrees C-light was approximate to 100%. When germinated under the light, seeds from the R treatment exhibited a higher germination percentage and a faster germination (under a broader range of temperatures) than seeds from the FR treatment. When germinated in the dark, seeds from the R treatment germinated 100% between 12 and 23 degrees C and over 50% at 30 degrees C, whereas seeds from the FR treatment germinated less than 35% between 12 and 23 degrees C and less than 5% at 30 degrees C. Seeds from the 11 treatment had lower abscisic acid (ABA) content and were better able to germinate when exposed to external ABA concentrations than seeds from the FR treatment. Seed longevity as assessed by the accelerated aging test was higher in seeds from the FR treatment, indicating that red-rich light was detrimental to longevity. In another experiment, lettuce seeds that developed under similar conditions were harvested at approximately the moment of maximum dry weight accumulation and desiccated in dark, far-red, red, or fluorescent + incandescent light. Seeds desiccated under red light exhibited higher dark germination than the other treatments; however, no differences were observed in thermoinhibition or longevity. These results suggest that lettuce seed produced in an environment with a high R:FR light ratio will exhibit reduced thermoinhibition and photosensitivity as compared with production in a lower R:FR light environment.
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    Restricted water availability during lettuce seed production decreases seed yield per plant but increases seed size and water productivity
    (AMER SOC HORTICULTURAL SCIENCE, 2008) Contreras, Samuel; Bennett, Mark A.; Tay, David
    Lettuce (Lactuca sativa) is an important vegetable crop worldwide, and its seed is commercially produced mainly under irrigation in and and semiarid regions. The objective of this study was to determine how water availability during seed development affects lettuce seed productivity and quality. Three experiments were performed in the greenhouse and growth chambers using lettuce (cv. Tango) cultivated in pots. When watering volume was restricted (dry treatment) from bolting to seed harvest to 54% of the well-watered control (wet treatment), plants were shorter, had reduced dry weight, and produced fewer and heavier seeds. Water productivity (seed yield/watering volume) was nearly 50% higher in the dry treatment. Seeds from the dry treatment had a modest improvement in seed vigor (assessed by seedling growth) and decreased germinability (higher sensitivity to exogenous abscisic acid and water potential) compared with the wet treatment. In another experiment, water stress was applied abruptly to well-hydrated lettuce plants with developing seeds. Seeds that were at one-third and two-thirds of physiological maturity when water was withheld had lower germinability and greater storability than seeds with no water restriction. These results provide information that may be used for improvement of irrigation practices for lettuce seed production.