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- Author or Editor: Daniel J. Cantliffe x
Glyphosate-resistant plants of `South Bay' lettuce (Lactuca sativa L.) were produced by using Agrobacterium tumefaciens containing a plasmid carrying glyphosate oxidase and EPSPS gene. An in vitro assay was performed to determine the sensitivity of `South Bay' leaf discs and seedling explants to varying glyphosate concentrations. The I50 for glyphosate leaf discs was 53.8 μm and for glyphosate seedlings 7.6 μm. There was a high correlation between the response of leaf discs and seedlings to glyphosate based on dry weight. These findings will allow identification of glyphosate-resistant transformants in an early stage of plant development, saving time and reducing the cost in generating an improved cultivar with the glyphosate resistance trait.
Abstract
Germinated pepper (Capsicum annuum L.) seeds were combined with plug-mix, or plug-mix and Liquagel or Laponite 445 gel at various concentrations and volumes of solution to determine their effects on plant stands and seedling growth. Treatments with pregerminated seed led to earlier, more uniform seedling emergence and larger seedlings than those with non-pregerminated seeds. Final plant stands were similar for both treatments. Plant stands and seedling growth were greater and more uniform with Liqua-gel gel mix formulations than Laponite. Seeds in planting mixes with high concentrations of Laponite (2.0% by volume) and large volumes of gel solution (1.75 liter per liter of plug-mix) in dry and moist soils emerged slower and resulted in lower and less uniform stands than the plug-mix treatments. The optimum gel mix medium for plant establishment (rate and total emergence, stand uniformity, and early seedling growth) consisted of 1.0 liter of plug-mix per 1.25 liters of gel solution at a Liqua-gel concentration of 1.0%.
Poor emergence and seedling vigor are common characteristics of many sweet corn (Zea mays L.) cultivars with the shrunken-2 (sh2) mutant endosperm. A rapid and reliable predictor of sweet corn seed field emergence would improve the potential for high quality crops. Field emergence of seven sh2 sweet corn cultivars grown at seven environments in Florida were correlated with laboratory vigor tests. Factor analysis was used to separate noncollinear vigor tests for subsequent multiple regression models. The best single predictor test (R 2 = 0.93***) was an index based on leachate conductivity and germination percentage after a complex stress vigor test involving incubation at 15C. Leachate conductivity after 3 h soaking at 25 or 30C (R 2 = 0.9W***), soil cold test (R 2 = 0.9***), alternate temperature stress conductivity test (R 2 = 0.88***), standard germination test at 30C (R 2 = 0.88***), and an index involving incubation at 25C (R 2 = 0.88***) were also good predictors of field emergence. Noncollinear tests including the towel germination test at 25 C and an alternate temperature stress conductivity test resulted in the best two factor predictor (r 2 = 0.89***), and with glutamic acid decarboxylase activity (GADA) was the best three factor predictor (r 2 = 0.93***). The index of conductivity and complex vigor test (ICS) evaluated seed membrane integrity and potential for pathogen infection, respectively, and can be considered as major factors affecting emergence in sh2 sweet corn.
Six transgenic `South Bay' lettuce lines (Lactuca sativa L.) with elevated levels of 5-enolpyruvyl shikimate-3-phosphate synthase (EPSPS) were evaluated for tolerance to the herbicide glyphosate. The six lines were selected from ≈150 independent transformation events using an Agrobacterium tumefaciens system. Three assay methods were used to identify gene expression with regard to glyphosate resistance. Leaf disks of the transgenic lines were cultured on media containing 0 to 1280 μm glyphosate. Leaf disks of the control had lower dry weight (DW) at 40 μm and greater glyphosate than all the transgenic lines. The transgenic lines continued to grow even at 1280 μm. Plants 21 days old were sprayed in the greenhouse with rates of glyphosate at 0 to 35.84 kg·ha-1. DW of all the lines were similar to the control, with a few exceptions, at glyphosate concentrations from 0 to 0.56 kg·ha-1. At 2.24 to 8.96 kg·ha-1 all of the transgenic lines had DW greater than the control, while at 17.92 and 35.84 kg·ha-1 only B-32, B-33, C-3, and C-14 had DW greater than the control. The resistant line from the greenhouse experiment, B-32, grew normally in field trials at the highest glyphosate rate, 17.92 kg·ha-1, while control plants died at 0.56 kg·ha-1 glyphosate. Lines A-11 and C-3 had lower DW than B-32 at 2.24 kg·ha-1 glyphosate and greater. While leaf disk assays can identify potential transformed lines expressing the EPSPS and glyphosate oxidase (GOX) gene, and greenhouse screening can evaluate seedling vigor after glyphosate application, field trials are necessary to evaluate plant growth and yield through the growing season. Chemical name used: N-(phosphono-methyl) glycine (glyphosate).
Ethylene synthesis and sensitivity, and their relation to germination at supraoptimal temperatures, were investigated in lettuce (Lactuca sativa L.) seeds matured at 30/20 °C [12-h day/night, high temperature matured (HTM)] or 20/10 °C [12-h day/night, low temperature matured (LTM)]. HTM seeds of both thermosensitive `Dark Green Boston' (DGB) and thermotolerant `Everglades' (EVE) had greater germination at a supraoptimal temperature (36 °C), in both light or dark, than LTM seeds of DGB and EVE. HTM seeds of DGB and EVE produced more ethylene during germination than LTM seeds, regardless of imbibition conditions. The ethylene action inhibitor, silver thiosulfate, led to reduced germination in both cultivars. The ethylene precursor, 1-aminocyclopropane-1-carboxylic acid at 10 mm increased germination of both cultivars at supraoptimal temperatures, whereas germination of HTM seeds was greater than that of LTM seeds. No differences in ethylene perception were detected between HTM and LTM germinating seeds using a triple response bioassay. This study demonstrated that at least one method through which seed maturation temperature influences lettuce germination is by affecting ethylene production.
To remain competitive for federal and state funding, state cooperative extension services must proactively incorporate issues programming and performance-based budgeting. State major program (SMP) design teams, which provide linkages between clientele groups and the research base, must conduct needs assessments to adjust to this new atmosphere of accountability. A case study illustrates how one Florida SMP (FL107, vegetable production, harvest, handling and integrated pest management in Florida) restructured its design team to become more flexible and proactive to target a wider range of outcomes. While still in the implementation phase, this model has already resulted in improved communication within the organization, better addressing extension needs at county level while facilitating reporting at the state level.
Frequent fertigation of soilless-grown bell pepper (Capsicum annuum L.) can increase fruit production, but development of fruit disorders may offset the increase in yield of first-quality (blemish-free) fruit in greenhouses with minimal environmental control. Fruit yield and quality were studied as affected by water volumes and nutrient concentration levels, delivered with irrigation events initiated after determined cumulative solar radiation levels, in ‘HA3378’ bell pepper from October to May in north–central Florida. Irrigation events occurred after solar radiation integral levels (SRI; ±SD) 1.7 ± 0.42, 3.7 ± 0.42, 5.7 ± 0.42, 7.7 ± 0.42, and 9.7 ± 0.42 kW·min−1·m−2, which led to mean number of daily irrigation events of 61 ± 31, 26 ± 12, 17 ± 8, 12 ± 5, and 10 ± 4 respectively. In peat mix, perlite, and pine bark media, volume per irrigation event and concentration levels of the nutrient solution were, in the first experiment, 74 mL standard (74-s), and in a second concurrent experiment, 74 mL half-standard (74-½s) or 3) 37 mL standard (37-s). In both studies, combined marketable fruit yields of first quality and second quality (minor cracking patterns and yellow spots) increased linearly with decreasing SRI (increased events per day). First-quality fruit weight with 74-s was unaffected by media and, in a quadratic response to SRI, reached 5.4 kg·m−2 at 5.7 kW·min−1·m−2. First-quality weight with 74-½s and 37-s did not differ. Weight was unaffected by SRI in peat mix and perlite, and a quadratic response was recorded in pine bark, with yields of ≤3.6 kg·m−2. Fruit cracking incidence decreased with increased SRI, and was generally greater in pine bark. Incidence of yellow spots doubled with 74-½s compared with 37-s, and decreased linearly with increased SRI; the disorder was minor with 74-s. Compared with 37-s, 74-½s decreased fruit with blossom-end rot by 14%, increased marketable fruit weight by 10% in media with the lowest water-holding capacity (perlite, pine bark), and increased nutrient use efficiency. With any media used, the SRI set point of 5.7 kW·min−1·m−2 (daily mean of 17 irrigation events) and 74 mL, at standard nutrient concentration levels, appeared to produce greater blemish-free fruit yield than delivering 37 mL/event or half-concentrated 74 mL/event within the range of SRI means of 1.7 to 9.7 kW·min−1·m−2 (61–10 irrigation events/day). Disorder-tolerant pepper cultivars, better temperature control, and August plantings are additional suggestions for irrigation management to increase first-quality fruit yield.
The influence of compost (derived from MSW and biosolids) maturity on seed germination of several weed species was evaluated. A bioassay was developed by extracting 20 g of compost of different maturities with various volumes of water, then measuring germination percentage of ivyleaf morningglory (Ipomoea hederacea) seeds placed on extract-saturated filter paper in a petri dish. A 20 g (dry weight) compost: 50 mL of water generated an extract that produced the widest percentage seed germination variation in response to composts of different maturity. Ivyleaf morningglory, barnyardgrass (Echinochloa crus-galli L.), purslane (Potulaca oleracea L.), and corn (Zea mays L) were selected as plant indicators to determine the compost maturity stage with maximum germination inhibition. Compost 8-week-old decreased percent germination, root growth, and germination index (combines germination rate and root growth), and increased mean days to germination (MDG) of each plant indicator. Immature 8 week-old compost extract effect on MDG and germination percent of 15 weed species was evaluated. Extract from 8-week-old compost inhibited germination in most weed species, except yellow nutsedge (Cyperus esculentus). Compost extracts derided from immature (3-day, 4-, and 8-week-old) compost resulted in delayed and reduced germination percent of important economic weed species.
A comparison of external morphology captured via a computer vision system and a study of internal anatomy of sweetpotato somatic embryos identified five different major morphological variants among torpedo and cotyledonary stage embryos. These included 1) Perfect Type, 2) Near Perfect Type, 3) Limited/No Meristematic Activity Type, 4) Disrupted Internal Anatomy Type, 5) Proliferating Type. Perfect and Near Perfect types of somatic embryos were categorized as competent, while Limited/No Meristematic activity, Disrupted Internal Anatomy, and Proliferating types were categorized as noncompetent with respect to their conversion ability. Lack of organized shoot development in somatic embryos of sweetpotato was attributed to the following abnormalities: 1) lack of an organized apical meristem, 2) sparsity of dividing cells in the apical region, 3) flattened apical meristem, 4) multiple meristemoids and/or diffuse meristematic activity throughout the embryo. A morphological fate map of most of the torpedo and cotyledonary embryo variants was identified, which will be beneficial in synthetic seeding and transgenic research and development of sweetpotato.
A system and methodology were developed for the nondestructive qualitative and quantitative analysis of volatile emissions from hydroponically grown `Waldmann's Green' leaf lettuce (Lactuca sativa L.). Photosynthetic photon flux (PPF), photoperiod, and temperature were automatically controlled and monitored in a growth chamber modified for the collection of plant volatiles. The lipoxygenase pathway products (Z)-3-hexenal, (Z)-3-hexenol, and (Z)-3-hexenyl acetate were emitted by lettuce plants after the transition from the light period to the dark period. The volatile collection system developed in this study enabled measurements of volatiles emitted by intact plants, from planting to harvest, under controlled environmental conditions.