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.
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.
Omega-3 fatty acids (O3FA) are essential for normal human growth, development, and disease prevention. Purslane (Portulaca oleraceaeL.) is an excellent source of the O3FA α-linolenic acid (LNA)—with higher concentrations than any green leafy-vegetable examined to date—and is being considered for cultivation (by USDA-ARS) in an effort to improve the balance of essential fatty acids in the western diet. Twenty-fi ve-day-old seedlings of both a green-leafed and a golden-leafed type of purslane were transplanted into a closed hydroponic system. Nitrogen, at 200 ppm, was provided as NO3 and NH4 forms to yield NO3: NH4 ratios of 1:0, 0.25:0.75, 0.5:0.5, and 0.75:0.25. Treatments were arranged in a randomized complete-block design with five replications. The experiment was repeated. Young, fully expanded leaves were harvested 18 days after treatment initiation, frozen (–60°C), and then analyzed for fatty acids using gas chromatography. Although the two types of purslane did not differ in LNA concentration, the green-leafed purslane produced greater total dry mass than the golden-type. On a leaf dry mass basis, plants grown with a NO3:NH4 ratio of 0.5:0.5 produced 241% and 53% greater LNA than plants grown with NO3:NH4 ratios of 1:0 and 0.75:0.25, respectively. Plants grown with NO3:NH4 ratios of 1:0 and 0.25:0.75 produced similar leaf LNA concentrations. Total dry mass was not affected by the nitrogen treatments.
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.
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.
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.
Purslane (Portulaca oleracea L.) has been identified as an exceptionally rich source of α-linolenic acid (LNA), an essential fatty acid that is beneficial in reducing the incidence of coronary heart disease and certain cancers. In general, about two thirds of the LNA in terrestrial plants is associated with chloroplasts. A green-leafed unnamed cultivar of purslane and a golden-leafed cultivar `Goldberg' were grown hydroponically in a complete nutrient solution with 14.3 mm nitrogen provided as nitrate (NO3-) and ammonium (NH4+) forms to yield NO3--N: NH4+-N ratios of 1:0, 0.75:0.25, 0.5:0.5, and 0.25:0.75. Young leaves, harvested 18 days after treatment initiation, were analyzed to determine the fatty acid composition and concentrations, and thylakoid protein and chlorophyll concentrations. Although the leaves of plants grown with a NO3--N: NH4+-N ratio of 0.5:0.5 contained 239% and 114% more LNA than plants grown with ratios 1:0 and 0.75:0.25, respectively, they contained only 41% and 26% more chlorophyll. The green-leafed cultivar had higher (39%) chlorophyll concentrations than `Goldberg', but both cultivars had similar LNA concentrations [per g dry weight (DW)]. These results suggest that the LNA concentration in the fatty acid-rich species P. oleracea may not be as closely associated with chlorophyll concentration as reported earlier for other plants. Leaves of plants grown in solutions with 0.25:0.75 NO3--N: NH4+-N ratio contained 35% less LNA per g leaf DW than the leaves of plants grown in nutrient solutions with a 0.5:0.5 ratio. Although total DW production was not affected by the NO3--N: NH 4+-N ratios in the nutrient solutions, the green-leafed cultivar produced higher fresh weight, leaf area, total DW, and number of shoots than `Goldberg'.
A study was initiated to identify cultural conditions that optimize the production of important chemopreventive agents in watercress. Chemopreventatives are chemical compounds that reduce or prevent diseases such as cancer. Watercress (Nasturtium officinale) contains phenylethyl glucosinolate that, on hydrolysis, yields PEITC, and PEITC is one of the most-important anti-carcinogens among the cruciferous chemopreventatives tested. Watercress was grown in closed hydroponic systems containing 200 ppm nitrogen and either 64, 128, and 192 ppm sulfur to yield N:S ratios of 1:0.3, 1:0.6, and 1:0.9. The experiment was laid out as RCBD in the greenhouse with six replications. PEITC levels in leaf and stem tissue was assayed using gas chromatograph. After 36 days in the treatment solutions, watercress grown at a N:S ratio of 1:0.6 produced 90.1% and 65.3% (in repeated experiments) more PEITC than plants grown at a N:S ratio of 1:0.3. Plants grown in nutrient solution with a N:S ratio of 1:0.9 produced 57.4% and 24.2% greater PEITC than those grown with a N:S ratio of 1:0.3. Plants grown in a nutrient solution with a N:S ratio of 1:0.9 produced 17.2% to 24.2% less PEITC than those grown with a N:S ratio of 1:0.6. Leaves contained 54% to 70% more PEITC per unit dry mass than stems, suggesting that the leaf is the major site of synthesis and storage of PEITC.
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.