Plant growth regulators (PGRs) are chemicals used on a wide range of horticultural crops. These exogenous chemicals, similar to endogenous plant hormones, regulate plant development and stimulate a desired growth response, such as control of plant height. One such PGR is abscisic acid (ABA), which has been used effectively to improve fruit quality, specifically sugars and phytonutrients. The purpose of this study was to examine the effects of exogenous applications of ABA on tomato (Solanum lycopersicum) fruit quality, such as carotenoids, soluble sugars and organic acids, and ABA on tomato leaf chlorophylls and carotenoids. Furthermore, this study compared how ABA and calcium (Ca) treatments together affect fruit quality and whether there are added benefits to treating plants with both simultaneously. ABA treatments proved effective in increasing tomato fruit soluble sugars and decreasing organic acid concentrations. This study demonstrated that ABA is a viable PGR to significantly improve tomato fruit quality, specifically pertaining to carotenoids, soluble sugar, and organic acid concentrations.
Purslane (Portulaca oleracea) is a succulent weedy annual in much of the United States. In other parts of the world, purslane is grown as a specialty crop, valued for its nutritional quality. As a leafy crop, purslane contributes carotenoid phytochemicals in the typical Mediterranean diet. Nitrogen (N) influences plant growth and alters pigment composition and accumulation. However, little is known about the impact N fertility may have on pigment concentrations in purslane shoot tissues. The objective of this study was to evaluate the influence of N fertility levels on biomass and concentrations of nutritionally important carotenoid and chlorophyll pigments in purslane. Green Leaf and Golden Leaf purslane cultivars were grown in nutrient solution culture under N concentrations of 13, 26, 52, or 105 mg·L−1. Plants were harvested at 45 days after planting (DAP), and measured for concentrations of shoot pigments using high-performance liquid chromatography (HPLC) methodology. There was no influence of N treatment concentration on purslane shoot tissue fresh weight (FW) accumulation. Nitrogen treatment significantly influenced shoot tissue β-carotene (BC), lutein (LUT), neoxanthin (NEO), total carotenoids, chlorophyll a, chlorophyll b, total chlorophyll, and the chlorophyll a to b ratio in purslane shoot tissues. Concentrations of LUT, NEO, violaxanthin (VIO), chlorophyll b, total xanthophyll cycle pigments, and the chlorophyll a to b ratio differed between the purslane cultivars. Increases in N concentrations acted to increase concentrations of nutritionally important shoot tissue carotenoid pigments in only the Green Leaf purslane cultivar. Therefore, N fertility management and cultivar selection should be considered when producing purslane as a nutritious specialty vegetable crop.
Ethylene effects were investigated on two tulip (Tulipa gesneriana L.) cultivars, Markant and Carreria. Pre-cooled bulbs were treated with ethylene (flow-through) for 1 week at 0, 0.1, 1.0, or 10 μL·L−1 (± 10%) in a modified hydroponic system. After ethylene exposure, plants were either destructively harvested for root measurements or forced in a greenhouse for flower measurements. Ethylene exposure at concentrations as low as 1 μL·L−1 during the first week of growth reduced shoot and root elongation and subsequently increased flower bud abortion. At 10 μL·L−1, root growth was essentially eliminated. In a second experiment, bulbs were treated overnight with 1-methylcyclopropene (1-MCP) before a 7-day exposure to 1 μL·L−1 ethylene. 1-MCP pretreatment eliminated the harmful effects of ethylene on root and shoot growth. This study illustrates the effects of ethylene exposure during hydroponic tulip production and demonstrates a potential benefit to treating bulbs with 1-MCP before planting.
Copper (electrolytically generated or from cupric sulfate) is increasingly used to control diseases and algae in the greenhouse industry. However, there is a shortage of information regarding appropriate management strategies for Cu2+ (Cu) in greenhouse hydroponic production. Three greenhouse studies were conducted to examine the growth and yield responses of sweet pepper (Capsicum annuum L., Triple 4, red) to the application of Cu in hydroponic production systems. In the first two experiments, plants were grown on rockwool and irrigated with nutrient solutions containing Cu at concentrations of 0.05, 0.55, 1.05, 1.55, and 2.05 mg·L–1. Copper treatments were started either when plants were 32 days old and continued for 4 weeks, or when plants were 11 weeks old and continued for 18 weeks, respectively. In the third experiment, roots of solution cultured pepper seedlings were exposed to Cu (1.0, 1.5, and 2.0 mg·L–1) containing nutrient solutions for 2 hours per day for 3 weeks. Higher Cu treatment initialized when plants were 32 days old significantly reduced plant leaf number, leaf area, leaf biomass, specific leaf area, stem length and shoot biomass. The calculated Cu toxicity threshold was 0.19 mg·L–1. However, when treatment initialized at plants were 11 weeks old, Cu did not have significant effects on leaf chlorophyll content, leaf area or specific leaf area. Copper started to show significant negative effects on leaf biomass and shoot biomass at 1.05 mg·L–1 or higher levels. Copper treatments did not have any significant effect on fruit number, fresh weight or dry weight. Under all the Cu levels, fresh fruit copper contents were lower than 0.95 mg·kg–1 which is below the drinking water standard of 1.3 mg·kg–1. Seedling growth was significantly reduced by exposing roots to Cu (≥1.0 mg·L–1) containing solutions even for only 2 h·d–1.
The present study was conducted to determine the critical optimum and toxic concentrations of potassium (K) using segmented analysis and its relationship with some physiological, anatomical, and nutritional responses to increasing K in hydroponically grown Lilium sp. L. cv. Arcachon. Plants were fertigated with nutrient solutions containing K (Kext) at 0, 2.5, 5.0, 7.5, 12.5, 17.5, 22.5, and 30 mmol·L−1. Maximum flower diameter occurred when, on a dry mass basis, shoot K (Kint) ranged from 504 to 892 mmol·kg−1; however, a lower Kint was required to obtain maximum biomass accumulation and shoot length (384 and 303 mmol·kg−1, respectively). Potassium increased in all plant organs as K in the nutrient solution increased. Nitrogen increased in young leaves and magnesium (Mg) decreased as Kext increased. Concentrations of Kext from 5 to 17.5 mmol·L−1 increased the size of chlorenchyma and occlusive cells; however, metaxylem vessels were unaffected. Net photosynthetic rate was higher in young leaves, whereas water potential increased in both young and mature leaves when Kext was greater than 22.5 mmol·L−1. Critical concentrations varied according to the growth parameter. Optimum Kint ranged from 303 to 384 mmol·kg−1 for vegetative parts, whereas parameters related with flower growth ranged from 427 to 504 mmol·kg−1. Concentration of 504 mmol·kg−1 Kint was associated with optimum growth for all the parameters assessed, whereas a Kint greater than 864 mmol·kg−1 was associated with a decline in growth; thus, these concentrations were considered as the critical optimum and critical toxicity levels, respectively. The optimum and toxicity critical Kint were estimated when Kext in the nutrient solutions was 5.6 and 13.6 mmol·L−1, respectively.
The evolution of plastic uses (excluding glazing) in the production of greenhouse vegetables is presented. Plastics are used in almost every aspect of crop production, including providing a barrier to the soil, lining crop production troughs, holding soil and soilless media, and providing a nutrient film channel. Irrigation systems have become very elaborate, with various plastic products used to transport water and nutrients and to provide a means of emitting nutrient solution to the crop. The greenhouse environment is managed from several plastic components, including air distribution tubes, shade materials, and energy curtains. Plastics are now common in greenhouse vegetable crop training, insect monitoring, postharvest handling, storage, and marketing.
Completely enclosed screen houses can physically exclude contact between the asian citrus psyllid [ACP (Diaphorina citri)] and young, healthy citrus (Citrus sp.) trees and prevent huanglongbing (HLB) disease development. The current study investigated the use of antipsyllid screen houses on plant growth and physiological parameters of young ‘Ray Ruby’ grapefruit (Citrus ×paradisi) trees. We tested two coverings [enclosed screen house and open-air (control)] and two planting systems (in-ground and container-grown), with four replications arranged in a split-plot experimental design. Trees grown inside screen houses developed larger canopy surface area, canopy surface area water use efficiency (CWUE), leaf area index (LAI) and LAI water use efficiency (LAIWUE) relative to trees grown in open-air plots (P < 0.01). Leaf water transpiration increased and leaf vapor pressure deficit (VPD) decreased in trees grown inside screen houses compared with trees grown in the open-air plots. CWUE was negatively related to leaf VPD (P < 0.01). Monthly leaf nitrogen concentration was consistently greater in container-grown trees in the open-air compared with trees grown in-ground and inside the screen houses. However, trees grown in-ground and inside the screen houses did not experience any severe leaf N deficiencies and were the largest trees, presenting the highest canopy surface area and LAI at the end of the study. The screen houses described here provided a better growing environment for in-ground grapefruit because the protective structures accelerated young tree growth compared with open-air plantings while protecting trees from HLB infection.
Responses of two hydroponically grown marigold species, Tagetes erects L. `pumpkin Crush' and T. patula L. `Janie Yellow', to Mn concentrations of 0.5 mg·liter-1 or 10 mg·liter-1 with KNO3 and Ca(NO3)2 (NO3 source) or NH4N O3 as the N source were investigated. In both species, Mn uptake was enhanced with the NO3 source while reduced with NH4NO3. With Mn supplied at 0.5 mg·liter-1 and NO3 as the N source, T. erects absorbed twice the Mn per gram of dry matter as T. patula. T. erecta accumulated higher concentration of Mn in the shoot than in the root irrespective of the N source. T. patula accumulated higher concentration of Mn in the roots with the NO3 source while NH4NO3 shifted the Mn accumulation to the shoot. Growth of both species was suppressed with 10 mg Mn/liter and the suppression was greater with the NO3 source than with the NH4NO3. These results indicate an interspecific response to Mn concentration as well as an N source influence on the uptake of Mn in marigold grown under hydroponic conditions.
This study evaluated the potential of high photosynthetic photon flux (PPF) from high-pressure sodium (HPS) lamps, alone or in combination with metal halide (MH) plus quartz iodide (QI) incandescent lamps, to support lettuce growth, with or without N supplementation. Varying exposures to radiation from combined HPS, MH, and QI lamps influenced dry weight gain and photosynthetic pigment content of hydroponically grown `Black-Seeded Simpson' lettuce (Lactuca sativa L.) seedlings. Cumulative leaf dry weight declined with increasing exposure, up to 20 hours per day, to 660 μmol·m-2·s-1 of photosynthetically active radiation (PAR) from HPS lamps concomitant with constant 20 hours per day of 400 m mol·m-2·s-1 from MH + QI lamps. Leaves progressively yellowed with increasing exposure to radiation from the three-lamp combination, corresponding to lower specific chlorophyll content but not to specific carotenoid content. Lettuce grown under 20-hour photoperiods of 400, 473, or 668 μmolm·m-2·s-1 from HPS radiation alone had the highest leaf dry weight at a PPF of 473 μmol·m-2·s-1. Chlorophyll, but not carotenoid specific content, decreased with each incremental increase in PPF from HPS lamps. Doubling the level of N in nutrient solution and supplying it as a combination of NH4 + and NO3 - partially ameliorated adverse effects of high PPF on growth and pigment content relative to treatments using single-strength N as NO3 –.