Growth and photosynthetic parameters were measured in Eustoma grandiflorum (Raf.) Shinn. ‘Umihonoka’ grown hydroponically under nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), or magnesium (Mg) deficiency in 1/2 strength of modified Johnson’s solution. Plant height, node number, and leaf area were all reduced under N, P, K, and Ca deficiencies but not under Mg deficiency as compared with plants grown in the complete nutrient solution. Shoot and root dry weight were reduced in the N-, P-, K-, and Ca-deficient treatments, whereas root but not shoot dry weight was lowered by Mg-deficient treatment. Shoot-to-root dry weight ratio decreased under N and P deficiencies, increased under K and Mg deficiency, but was not altered under Ca deficiency. Decreased net photosynthetic rate (Pn) of N-, P-, and K-deficient leaves was all related to lower stomatal conductance (g S), whereas N-deficient leaves also accompanied by a higher intercellular carbon dioxide concentration (Ci). The Mg-deficient treatment did not alter chlorophyll fluorescence Fv/Fm, maximal fluorescence (Fm), or minimal fluorescence (Fo). Decreased Fv/Fm of N-, P-, K-, and Ca-deficient leaves was all related to lower Fm, whereas N- and P-deficient leaves also accompanied by lower Fo. A key was developed for the identification of N, P, K, Ca, and Mg deficiency symptoms.
Host nutritional variables were evaluated for their effects on the severity of crown and root rot of tomato caused by Fusarium oxysporum f.sp. radicis-lycopersici. Tomato (Lycopersicon esculentum Mill.) seedlings (cv. Bonnie Best) were grown in a pathogen-infested, soilless rockwool system in the greenhouse and were fertilized with a nutrient solution that was amended with macro- and microelements at various rates. Disease was evaluated after 2 weeks using an index of 0 to 4, and plant fresh weight was measured. Regression analysis indicated that disease severity was significantly increased by ammonium-nitrogen [NH4Cl, (NH4)6Mo7O24, and (NH4)2SO4], NaH2PO4·H2O, Fe-EDDHA, MnSO4, MoO3, and ZnSO4·7H2O. Disease severity was reduced by nitrate-nitrogen [Ca(NO3)2·4H2O] and CuSO4·H2O. Low rates of NH4NO3 (39 to 79 mg·L-1 N) reduced disease, but rates above 100 mg·L-1 N increased it. Disease was not affected by MgSO4·7H2O. In all cases, plant growth was inversely related to disease severity. Mineral fertilizers had no effect on nutrient solution pH. This information sheds new light on environmental factors that influence plant-pathogen interactions, and may be applied to develop a management strategy for Fusarium crown and root rot based on host nutrition.
Sweet corn (Zea mays L.) cultivars containing the shrunken-2 (sh2 ) gene have superior kernel quality but often germinate poorly and display poor seedling vigor. The transplanting of sh2 sweet corn was investigated as a method to improve stand establishment and hasten maturity. Three-week-old plants (sh2 cv. Krispy King) were raised in 200-cell polystyrene trays in either plug-trays (PT), float beds (FB), or ebb-and-flood (EF) production systems and compared with direct-seeded (DS) controls for transplant quality, successful establishment, and early harvest. In 1994, when plants were established in early June, PT plants matured 1 week earlier than DS and FB plants, which had similar mean times to harvest. In 1995, when field planting occurred in July, all plants flowered prematurely when only 60 cm tall. In 1996, the experiment was begun in early May, and survival of all transplants was >85% vs. 54% for DS plants. In 1996, transplants matured 10 to 13 days earlier than DS plants, however, >90% of DS plants produced marketable ears vs. 63%, 49%, and 44% of EF, FB, and PT plants, respectively. The DS plants were also taller with better root development than transplants in all years. Transplants produced smaller, lower-quality ears than did DS plants, thus nullifying the benefits of greater plant populations and earlier maturity. The EF system produced high-quality seedlings because of the greater control of water availability during seedling development. In some areas, the increased value of early sh2 sweet corn may be worth the additional cost of transplanting and greater percentage of unmarketable ears.
We recently showed that spinach (Spinacia oleracea L.) transplants produced under a short photoperiod and low air temperature were characterized by a delay of bolting and short flower-stalk length at harvest (Chun et al., 2000a). The present study was conducted to determine whether these changes are caused by the short photoperiod itself or by the lower integrated photosynthetic photon flux (IPPF). Shoot and root dry weights of transplants increased significantly with increasing IPPF, but were not affected by a change in the photoperiod. However, the floral development indices of transplants were significantly greater under a 16-than under a 10- or 13-hours/day photoperiod, but were not affected by a change in IPPF. The percentage of bolted plants 3 days after transplanting (DAT) increased significantly with increasing photoperiod (from 0% at 10 hours/day to more than 85% at 16 hours/day). Flower-stalk length increased with increasing photoperiod (e.g., at 14 DAT, from 15 mm at the shorter photoperiods to 80 mm at 16 hours/day), but was not affected by a change in IPPF. These results show that the delay of bolting that occurs when the photoperiod is reduced during transplant production is due to the delay of floral development and not to retarded vegetative growth as a result of reduced IPPF.
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.
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.