Browsing by Author "Contreras, Samuel"
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- ItemCharacterisation 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, SamuelThe 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.
- ItemHigh Nitrogen Fertilization Decreases Seed Weight but Increases Longevity in Tomato Seeds(2022) Sanchez, Javier; Albornoz, Francisco; Contreras, SamuelNitrogen fertilization is a key practice in agriculture and its effects on yield and quality of most commodity products are widely known. However, the response of seed production to N fertilization, especially with regard to its effects on seed quality, is still poorly understood. The objective of this study was to determine the effect of N fertilization on tomato seed yield and quality. Six quality attributes were assessed (weight, standard germination, germination rate under normal and adverse conditions, dormancy and longevity) in tomato cv. Moneymaker plants fertigated with one of three nutrient solutions differing in their N concentration: 5, 15 or 25 mM. Seed weight decreased by 4% with increasing N fertilization while standard germination and mean germination time did not vary among treatments, with average values of 89.7% and 6.2 days, respectively. The percentage and rate of germination decreased when seeds were imbibed in solutions with reduced osmotic potential; however, this effect was less pronounced in seeds from the 25 mM treatment, indicating a lower dormancy. When germination was evaluated after accelerated aging, seeds from the high N fertilization treatment showed greater longevity. These results contribute to optimizing fertilization practices for the production of high quality tomato seeds.
- ItemIdentificación 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, PatriciaIntroducción: 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.
- ItemMaternal 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, DavidSeed 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.
- ItemRed 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, HaimThermoinhibition 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.
- ItemRestricted 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, DavidLettuce (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.
- ItemSeed Morpho-Anatomy, Dormancy and Germination Requirements in Three Schizanthus Species (Solanaceae) with Ornamental Potential(2024) Moreno, Joaquin; Gomez, Miguel; Contreras, SamuelSchizanthus carlomunozii, S. hookeri, and S. porrigens are herbaceous species native to Chile and Argentina and have high ornamental potential. Their propagation through seeds is challenging due to low and uneven germination percentages. This study aimed to determine the morpho-anatomical characteristics, dormancy, and germination requirements of the seeds of these three species. The seeds from all three species have a flattened and reniform shape with a foveolate testa. However, the seeds of S. hookeri are distinguished by their larger size, more pronounced C-shape, seed coat with more marked prominences, and symmetrically arranged areoles. Histological analysis and imbibition tests with methylene blue revealed that the seeds have well-developed embryos and permeable seed coats, ruling out physical and morphological dormancy. Germination tests under various conditions showed that the seeds of the three species exhibit physiological dormancy. Imbibition in gibberellic acid (200 ppm) proved to be an effective treatment to promote germination. When evaluated in S. hookeri seeds, cold stratification and after-ripening also improved germination. The optimal temperatures for seed germination were calculated to be 26 degrees C for S. carlomunozii, 19 degrees C for S. hookeri, and 23 degrees C for S. porrigens.
- ItemSeeds Yield and Quality of Quinoa ( Chenopodium quinoa Willd.) Plants Grown Under Different Nitrogen Fertilization Doses(2024) Contreras, Samuel; Molina, Jorge; Garcia, Margarita; Sanchez, Javier; Chorbadjian, Rodrigo; Fuentes, Francisco; Albornoz, FranciscoS. Contreras, J. Molina, M. Garc & iacute;a, J. S & aacute;nchez, R. Chorbadjian, F. Fuentes, and F. Albornoz. 2024. Seeds Yield and Quality of Quinoa (Chenopodium quinoa Willd.) Plants Grown Under Different Nitrogen Fertilization Doses. Int. J. Agric. Nat. Resour. 68-74. Quinoa ( Chenopodium quinoa Willd.) has been cultivated for more than 7,000 years in the mountain regions (Andes Mountains) of South America. Five ecotypes differing in their phenology, morphology and stress resistance can be found. One of these ecotypes corresponds to the coastal ecotype, which is cultivated mainly in Chile. Little information is available regarding the response of this ecotype to nitrogen (N) fertilization. In the present study, three N fertilization doses (low: 30, adequate: 140 and high: 280 kg ha -1 ) were evaluated in plants grown in containers. Seed yield and quality attributes, including seed weight, nitrate content, germination, and seed longevity, were evaluated. These results indicate that increasing N fertilization promotes increases in seed yield and weight. In terms of seed quality, although the fertilization treatments did not affect germination, seed longevity was reduced by increasing the N fertilization dose.