Browsing by Author "Bennett, Mark A."

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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.