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  • Author or Editor: Richard J. McAvoy x
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In this paper we review our research of light effects on tomato production. It was demonstrated that, during the production of greenhouse tomatoes, the total fruit yield, as well as time of harvest, was related to light. The date of harvest was inversely correlated with the amount of light the crop received during the seedling phase of growth, while fruit weight was positively correlated with light during the production phase. Additionally, we present information that shows that light was most effective in promoting fruit development between 15 and 45 days after flowering. Some of these relationships were quantified and used to develop a predictive model to help a grower plan a tomato crop to meet market demand. The concept of the Single-cluster Tomato Production System was developed, and the rewards of using our understanding of plant-environment interactions to control plant growth and, therefore maxim&profits were shown. Furthermore, the need to create a more dynamic model and the methods for doing so were discussed.

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Subirrigation for production of potted ornamental plants reduces the waste of water and fertilizer inherent to conventional overhead watering systems used in greenhouses. Ebb and flow watering systems for flooded floors typically operate slowly so that the substrate takes up water to near effective water-holding capacity during each irrigation event. We used a system that rapidly delivered water to and removed water from the production surface to restrict the water provided to the plants. We examined several parameters that vary between this fast-cycle ebb and flow watering on a flooded floor compared with slow-cycle watering. Water and fertilizer use was reduced by 20% to 30% with fast- compared with slow-cycle watering. Biomass and stem height at bloom were also reduced by 10% to 20% under fast-cycle saturation. This watering method did not affect the rate of flower development or plant nutrient composition. Volumetric water content of the substrate was the only measure that was affected by location on the flooded floor. Despite the fast ebb and flow on pitched floors, none of the aspects of plant growth was affected by location on the floor. This method of watering shows promise as a means to produce uniform crops of container-grown plants while conserving water and fertilizer.

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Abstract

Tomato plants (Lycopersicon esculentum Mill. cv. Laura), pruned to a single-flower truss, were exposed to 90 μmol·s−1·m−2 supplemental photosynthetic lighting (0400 to 2200 hr) during the developmental period: a) anthesis to initial fruit set, b) anthesis to mature-green fruit, or c) anthesis to red-ripe fruit. The yield response was compared to plants receiving d) no supplemental photosynthetic lighting after incipient anthesis. The greatest increase in average fruit weight was produced with continued supplemental lighting during the developmental-period initial fruit set to the mature-green stage. Net photosynthetic activity, μmol CO2/min per dm2, was the greatest in the canopy during early anthesis and then steadily declined as the canopy aged. Net whole plant photosynthetic activity, μmol CO2/min per plant, increased steadily after the early anthesis stage of development to a peak rate during the rapid fruit development stage. Net whole plant photosynthetic activity then declined as the plant approached the mature-green and then finally the red-ripe stage of fruit development.

Open Access

Cytokinins play an important role in regulating plant growth and development. The cytokinin gene, isopentenyl transferase (ipt), was placed under the control of the ACC oxidase promoter from the LEACO1 gene from Lycopersicon esculentum and introduced into Nicotiana tabacum (cv. Havana) and chrysanthemum (Dendranthema × grandiflorum `Iridon'). Transformants were confirmed by PCR reaction and Southern blot and analyzed for phenotypical changes under both greenhouse and growth chamber conditions. With both species, LEACO1-ipt transgenic plants displayed a wide range of vegetative and generative phenotypes. With plants growing in the vegetative state, some LEACO1-ipt transgenic lines appeared similar to the non-transgenic wild-type cultivars while other lines showed excessive lateral branch development and short internodes. With plants grown under generative conditions, several LEACO1-ipt transgenic lines showed a 2 to 10-fold increase in the number of flower buds relative to the wild-type cultivars. With chrysanthemum, dramatic increases in bud count were observed on transgenic lines that otherwise displayed a morphology similar to the non-transgenic lines. Analysis of ipt expression indicated a marked change in gene expression between the most extreme phenotypes observed in this study. LEACO1-ipt lines that express normal vegetative development but increased flower bud counts appear to have great potential for ornamental crop improvement.

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It has been reported that constitutive expression of the fatty acid desaturase enzyme increased the trienoic fatty acid content of thylakoid membranes in transgenic tobacco, allowing the membranes to remain fluid under cold conditions. While increased cold tolerance resulted from this genetic modification, plants with a constitutively expressed desaturase enzyme would not be particularly well suited for growth under warm temperatures. To increase the ability of plants to tolerate prolonged cold-storage and still perform under greenhouse production conditions (25 °C), a unique cold-inducible genetic construct was cloned and tested. The FAD7 gene, which encodes an omega-3-fatty acid desaturase enzyme, was put under the control of a cold-inducible promoter (cor15a) from Arabidopsis thaliana. Transgenic petunia plants (cv, Marco Polo Odyssey) harboring cor15a:FAD7 were established and conformed by PCR and Southern analysis. Therefore in our study, FAD7 gene expression was induced by exposure to cold temperatures and down regulated under normal growing conditions. RT-PCR indicated a marked increase in FAD7 expression between transgenic plants exposed to a short (3 days) cold treatment prior to long-term cold storage and those that did not receive a cold induction treatment. Transgenic and wild-type plants were induced in cold (3 °C) for 3 days, returned for normal greenhouse conditions for 5 days and then subjected 3 weeks of continuous cold storage. It was observed that two out of eight transgenic lines showed superior cold tolerance relative to wild-type petunia plants. Additionally, plants that showed cold tolerance completely recovered; growing and flowering normally when returned to the 25 °C greenhouse conditions.

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The bacterial isopentenyl transferase (ipt) gene involved in cytokinin biosynthesis was fused with a promoter from the serine proteinase inhibiter (win3.12) gene of Populus x generosa and introduced into Nicotiana tabacum (cv. Havana). Transformants were confirmed by PCR reaction and Southern blot analysis, and then analyzed for phenotypic characteristics. RT-PCR analysis detected transcripts of the ipt gene following the wounding of win3.12:ipt transgenic plants. In win3.12: ipt transgenic plants, lateral shoot number and the diameter of lateral branches that developed following apical shoot removal increased relative to wild-type plants. However, the increase in cytokinin production following wounding appeared to be short lived. The potential utility of this construct in enhancing lateral branching in ornamental crops will be discussed.

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Poinsettias were grown in a closed hydroponic system with a modified Hoagland's solution concentration of either 1 or 3 mS·cm-1. Water use and whole plant fresh mass were measured gravimetrically at 2 to 3 day intervals over an eleven week period (initial break development through full bract development). At two week intervals, poinsettias were harvested and the fresh and dry mass of leaves, bracts stems, and roots were determined, and total laminar surface area was measured. Leaf temperature (LT), root-zone solution temperature (RZT), and at canopy level, air temperature (CAT), VPD, and photosynthetic photon flux (PPF) were monitored at 1 mm intervals and mean values recorded each 30 mm using a 21X micrologger (Campbell Scientific, Logan Utah). Water use (ml·dm-2·day-1) averaged 15% higher for poinsettias grown in the 1 mS·cm-1 solution than in the 3 mS·cm-1 nutrient solution. Simple linear regression of daily water use with PPF, or VPD, or CAT, while significant, accounted for less than half of the daily fluctuation in water use (r2; PPF= 0.47, VPD=0.21, CAT=0.30). However, multiple regression involving daily PPF, VPD, CAT, RZT and LT accounted for up to 82% of the variation in daily water use.

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Purslane (Portulaca oleracea L.) is an excellent source of the essential fatty acid α-linolenic acid (LNA) but little is known of the effects of cultural conditions on LNA concentration. Purslane seedlings were grown under an instantaneous photosynthetic photon flux [PPF (400 to 700 nm)] of 299 or 455 μmol·m-2·s-1 for a daily duration of either 8, 12, 16, or 20 hours. Thus, plants were exposed to a daily PPF of 8.6, 12.9, 17.2, or 21.5 mol·m-2·d-1 in the low PPF treatment (299 μmol.m-2.s-1) and 13.1, 19.7, 26.2, or 32.8 mol·m-2·d-1 in the high PPF treatment (455 μmol·m-2·s-1). Plants in all treatments received a 20-hour photoperiod by providing ≈5 μmol·m-2·s-1 from incandescent lamps starting at the end of the photosynthetic light period. At low PPF, purslane grown under a 16 hour PPF duration produced the highest concentrations of total fatty acids (TFA) and LNA per unit leaf dry weight (DW), but at high PPF, concentrations of these compounds were highest under 8 and 12 hour PPF duration. Trend analysis indicated that maximum TFA and LNA concentrations occurred with a daily PPF of 14.1 and 17.2 mol·m-2·d-1, respectively; and in the thylakoids, protein, chlorophyll, and LNA concentrations peaked at a PPF of 21.8, 19.9, and 16.1 mol·m-2·d-1, respectively. LNA as a percentage of TFA was unaffected by treatment. Shoot DW increased with PPF up to the highest PPF exposure of 32.8 mol·m-2·d-1.

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The early onset of bract necrosis in poinsettia (Euphorbia pulcherrima Willd. ex. Klotzch) is characterized by small dark-stained spots that precede the development of enlarged necrotic lesions. Electron micrographs of adaxial epidermal and subepidermal tissues with early symptoms of necrosis revealed large, electron-dense deposits in cell vacuoles. These spherical bodies resembled condensed tannins observed in the epidermal tissues of peach and apple fruit. Chemical analysis of bract tissues confirmed the presence of condensed tannins. Furthermore, there were higher concentrations of condensed tannin in bract samples with 2-mm-diameter lesions than in samples with lesions <0.5 mm (equivalent to catechin concentrations of 59 and 13 mg·g-1 fresh mass, respectively). No tannin bodies were observed in parallel samples of healthy-appearing bracts in which only trace concentrations of condensed tannins were measured (0.2 mg·g-1 fresh mass). The evidence suggests an association between condensed tannin accumulation in localized areas of the bract and the early appearance of bract necrosis symptoms.

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