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Boron (B) is an essential plant micronutrient. Two major B-transport proteins have been recently identified and partially characterized: BOR1, a high-affinity B efflux transporter involved in xylem loading, and NIP5;1, a plasma-membrane boric-acid channel involved in B uptake. To date, studies of these B transporters have investigated their expression individually (mainly as mRNA), and only in response to variation in B availability (mostly B deficiency); the influence of other factors, such as plant resource status, has not been studied. To address this, we grew geranium (Pelargonium × hortorum cv. Maverick White) plants under ambient or elevated CO2 concentration, different sub-saturating irradiances, and different B availability. For comparison we also grew three other species (Arabidopsis thaliana, Azolla caroliniana, and Hordeum vulgare) under broad range of B supply. Relative accumulation of BOR1 and NIP5;1 proteins were measured using protein-specific antibodies and Western blotting or ELISA. Elevated CO2 significantly increased content of NIP5;1, while increases in irradiance increased BOR1 content, but decreased NIP5;1 content. Across species, content of both transporters often decreased with increasing B availability, but sometimes remained unchanged or even increased, depending on CO2, irradiance, species, or transporter. Content of BOR1 and NIP5;1 was correlated with root proteins, B content, and sugar content (for high CO2 only), as well as B uptake, but CO2 and irradiance often affected these relationships. Thus, relative accumulation of BOR1 and NIP5;1 is influenced not only by B content, as expected, but by other environmental factors as well.

‘Bouquet Purple’ pinks (Dianthus sp.) were grown in silica-sand culture to induce and photograph symptoms of nutritional disorders. Plants received a complete modified Hoagland's all-nitrate (NO3) solution. Nutrient-deficient treatments were induced with a complete nutrient formula minus one of the nutrients, and a boron (B)-toxicity treatment was induced by increasing B 10-fold in the complete nutrient formula. Plants were monitored daily to document sequential series of symptoms as they developed. Typical symptomology of nutrient disorders and corresponding tissue concentrations were determined. All treatments exhibited deficiency symptomology. Disorders for nitrogen (N), iron (Fe), calcium (Ca), and sulfur (S) were the first to manifest in pinks. Unique symptomology was observed for plants grown under potassium- (K), B-, copper- (Cu), and molybdenum- (Mo) deficient conditions, which supported the need for a species-specific approach when characterizing nutrient disorders of floriculture crops.

The 5-day sodium carbonate-ammonium nitrate extraction assay (5-day method) has been recognized by the American Association of Plant Food Control Officials as a validated test method to identify fertilizers or beneficial substances that provide plant-available silicon (Si). The test method used the molybdenum blue colorimetric assay to quantify percentage Si; however, laboratories may use inductively coupled plasma optical emission spectroscopy (ICP-OES) for elemental analysis. To examine the use of either colorimetric or ICP-OES methods for Si determination, the 5-day method was performed on the following Si-containing compounds; wollastonite, sand, biochar, and a basic oven furnace (BOF) slag. Grow-out studies using Zinnia elegans were also performed using varying rates of the wollastonite, biochar, and BOF slag. Our results show using the 5-day method, wollastonite had the highest extracted amounts of silicic acid (H4SiO4) at 4% followed by biochar (2%), BOF slag (1%), and sand (0%). Extraction values calculated using either the molybdenum blue colorimetric assay or ICP-OES for detection of the H4SiO4 had a significant correlation, supporting the application of either detection method for this type of analysis. However, when extracted values were compared to amounts of Si taken up by the plants, the 5-day method overestimated both wollastonite and biochar. While this method is a valid indicator test for determining a soluble Si source, other plant species and methods should be perused to potentially provide more quantitative analyses for plant-available Si content of all materials.

Senecio cineraria ‘Silver Mist’ plants were grown in silica sand culture to induce and photograph nutritional disorder symptoms. Plants were grown with a complete modified Hoagland’s all nitrate solution: (macronutrients in mM) 15 NO3-N, 1.0 PO4-P, 6.0 K, 5.0 Ca, 2.0 Mg, and 2.0 SO4-S, plus µM concentrations of micronutrients, 72 Fe, 18 Mn, 3 Cu, 3 Zn, 45 B, and 0.1 Mo. The nutrient deficiency treatments were induced with a complete nutrient formula minus one of the nutrients. Reagent grade chemicals and deionized water of 18-mega ohms purity were used to formulate treatment solutions. Boron toxicity was also induced by increasing the element 10A— higher than the complete nutrient formula. The plants were automatically irrigated. The solution drained from the bottom of the pot and was captured for reuse. A complete replacement of nutrient solutions was done weekly. Plants were monitored daily to document and photograph sequential series of symptoms as they developed. Typical symptomology of nutrient disorders and critical tissue concentrations are presented.

Dahlia A— hybrida ‘Maxi Morelia’ plants were grown in silica sand culture to induce and photograph symptoms of nutritional disorders. Plants were grown with a complete modified Hoagland’s all nitrate solution: (macronutrients in mM) 15 NO3-N, 1.0 PO4-P, 6.0 K, 5.0 Ca, 2.0 Mg, and 2.0 SO4-S, plus µM concentrations of micronutrients, 72 Fe, 18 Mn, 3 Cu, 3 Zn, 45 B, and 0.1 Mo. The nutrient deficiency treatments were induced with a complete nutrient formula minus one of the nutrients. Reagent grade chemicals and deionized water of 18-mega ohms purity were used to formulate treatment solutions. Boron toxicity was also induced by increasing the element 10A— higher than the complete nutrient formula. The plants were automatically irrigated. The solution drained from the bottom of the pot and was captured for reuse. A complete replacement of nutrient solutions was done weekly. Plants were monitored daily to document and photograph sequential series of symptoms as they developed. Typical symptomology of nutrient disorders and critical tissue concentrations are presented.

Fuchsia A— hybrida ‘Gartenmeister Bonstedt’ plants were grown in silica sand culture to induce and photograph nutritional disorder symptoms. Plants were grown with a complete modified Hoagland's all nitrate solution: (macronutrients in mM) 15 NO3-N, 1.0 PO4-P, 6.0 K, 5.0 Ca, 2.0 Mg, and 2.0 SO4-S, plus µM concentrations of micronutrients, 72 Fe, 18 Mn, 3 Cu, 3 Zn, 45 B, and 0.1 Mo. The nutrient deficiency treatments were induced with a complete nutrient formula minus one of the nutrients. Reagent grade chemicals and deionized water of 18-mega ohms purity were used to formulate treatment solutions. Boron toxicity was also induced by increasing the element 10A— higher than the complete nutrient formula. The plants were automatically irrigated. The solution drained from the bottom of the pot and was captured for reuse. A complete replacement of nutrient solutions was done weekly. Plants were monitored daily to document and photograph sequential series of symptoms as they developed. Typical symptomology of nutrient disorders is presented.

In our previous study on geranium, we showed that increases in growth irradiance from sub-optimal to near-optimal could delay boron deficiency effects on photosynthesis. In this study, we further investigated the effects of growth irradiance on tolerance to B stress by growing geranium (Pelargonium × hortorum cv. Maverick White) under sub- to supra-optimal B concentrations (4.5, 45, and 450 μM) and under three irradiances of 100, 300, or 500 μmol m−2 s−1 PAR for 30 d. In general, at low and medium irradiances, sub- and supra-optimal B availability decreased root and shoot dry masses, but at high irradiance, the B stress was prevented. Net photosynthetic rate decreased by the supra-optimal B concentration at the high irradiance only suggesting B-related photoinhibition. Tissue B content and root specific B uptake only modestly decreased by the low B treatment, but increased greatly by the high B availability, and the higher irradiance decreased the tissue B content and the root B uptake only at the low and medium B supplies. Interestingly, the increases in irradiance decreased the content and uptake of all other nutrients, except Fe uptake. Effects of the B stress on the content of other nutrients were variable, but the B stress often exacerbated decreases in nutrient content with the increasing irradiance which would be especially important under nutrient-limiting conditions. Hence, in this study, the B stress effects on growth were mitigated by the increases in growth irradiance, which offset negative effects on physiology, and the protective effects of irradiance were likely caused by its positive effects on plant carbon/energy status rather than on tissue B content or B uptake.

Global warming will increase heat waves, but effects of abrupt heat stress on shoot–root interactions have rarely been studied in heat-tolerant species, and abrupt heat-stress effects on root N uptake and shoot C flux to roots and soil remains uncertain. We investigated effects of a high-temperature event on shoot vs. root growth and function, including transfer of shoot C to roots and soil and uptake and translocation of soil N by roots in the warm-season drought-tolerant C 4 prairie grass, Andropogon gerardii . We heated plants in the lab and field (lab = 5.5 days at daytime of 30 + 5 or 10 °C; field = 5 days at ambient (up to 32 °C daytime) vs. ambient +10 °C). Heating had small or no effects on photosynthesis, stomatal conductance, leaf water potential, and shoot mass, but increased root mass and decreased root respiration and exudation per g. 13 C-labeling indicated that heating increased transfer of recently-fixed C from shoot to roots and soil (the latter likely via increased fine-root turnover). Heating decreased efficiency of N uptake by roots (uptake/g root), but did not affect total N uptake or the transfer of labeled soil 15 N to shoots. Though heating increased soil temperature in the lab, it did not do so in the field (10 cm depth); yet results were similar for lab and field. Hence, acute heating affected roots more than shoots in this stress-tolerant species, increasing root mass and C loss to soil, but decreasing function per g root, and some of these effects were likely independent of direct effects from soil heating.

Gazania rigens ‘Daybreak White’ plants were grown in silica sand culture to induce and photograph symptoms of nutritional disorders. Plants were grown with a complete modified Hoagland’s all nitrate solution: (macronutrients in mM) 15 NO3-N, 1.0 PO4-P, 6.0 K, 5.0 Ca, 2.0 Mg, and 2.0 SO4-S, plus µM concentrations of micronutrients, 72 Fe, 18 Mn, 3 Cu, 3 Zn, 45 B, and 0.1 Mo. The treatments causing nutrient deficient symptoms were induced with a complete nutrient formula minus one of the nutrients. Boron toxicity was also induced by increasing the element 10× higher than the complete nutrient formula. Reagent grade chemicals and deionized water of 18-mega ohms purity were used to formulate treatment solutions. The plants were automatically irrigated. The solution drained from the bottom of the pot and was captured for reuse. A complete replacement of nutrient solutions was done weekly. Plants were monitored daily to document and photograph sequential series of symptoms as they developed. Typical symptomology of nutrient disorders and critical tissue concentrations are presented. Out of the thirteen treatments, eleven exhibited symptoms. Deficiency symptoms of N, S, and Ca were first to manifest. Should nutritional disorders arise growers should first consider these three problems when trying to determine the possible cause.

Solenostemon scutellarioides ‘Lime Light’ were grown in silica-sand culture to induce and catalog nutritional disorder symptoms. Plants were grown with a complete, modified Hoagland’s solution (macronutrients in mM, micronutrients in µM): 15.0 NO3-N, 1.0 PO4-P, 6.0 K, 5.0 Ca, 2.0 Mg, 2.0 SO4-S, 72.0 Fe, 18.0 Mn, 3.0 Cu, 3.0 Zn, 45.0 B, and 0.1 Mo. The control plants were grown using a nutrient formula containing all essential nutrients. Each nutrient deficiency treatment was induced by using the complete formula minus only one essential nutrient. Reagent grade chemicals and deionized water of 18-mega ohms purity were used to formulate treatment solutions. Toxicity of boron was also induced by increasing the element 10X higher than the complete formula. Plants were automatically irrigated every 2 hours, drained from the pot bottom and solution captured for reuse. The nutrient solutions were replaced weekly. Researchers monitored plants daily to document and catalog sequential onset of symptoms. Symptoms of N, P, Ca, Fe deficiency and B toxicity were the first disorders to exhibit in Solenostemon scutellarioides ‘Limelight’. The chartreuse coloration of this cultivar compounded difficulties in assessing symptomology of some nutrient disorders, particularly those that manifested with yellowing discoloration or chlorosis.

Two warm-season bedding plant species, zinnia (Zinnia elegans) and vinca (Catharanthus roseus), were used to determine if phosphorus (P) supply should be adjusted with light supply, and if deficiency and/or oversupply symptoms were apparent at different P rates when growth rates were altered by light levels. An additional goal was to determine the influence of P and light on overall P uptake efficiencies and water use efficiencies. Plants were grown in a greenhouse with or without shade over portions of the bench and supplied 0.1, 0.2, 0.5, 1, 2, or 4 mm P along with complete nutrient solution as needed with no leaching fraction. Optimum plant growth and flower development rate occurred at a P supply of 0.5 mm regardless of the light supply. Plant growth was greatly reduced by P supply below 0.5 mm regardless of shade conditions. Tissue P concentration was not influenced by light, but overall P content (mg P per plant) was higher when plants were grown without shading as a result of larger plants in higher light environments. The appearance or severity of deficiency symptoms also was not influenced by light. Water use efficiency was maximized when growth was not limited by P supply (at or above 0.5 mm). One hundred percent recovery of applied P was obtained at the 0.5 mm P supply in vinca, whereas recovery was less at the same P supply in zinnia. These results indicate no benefit for plant growth and flowering to P supply above 0.5 mm and illustrate how P content is demand-driven. However, there was no induction or delay of nutrient stress symptoms as a result of different plant growth rates in the different light differences environments.

In spite of several published studies we have an incomplete understanding of the ion-release mechanisms and characteristics of polymer-coated fertilizers (PCF). Here we extend current conceptual models describing release mechanisms and describe the critical effects of substrate moisture and temperature on macro- and micronutrient release of three PCF types: Polyon ® , Nutricote ® , and Osmocote ® . Nutrient release was quantified at weekly intervals for up to 300 d from 5°C to 40°C in water and chemically inert sand, substrates that allowed release quantification without confounding effects of ion sorption/desorption. At least two release-timeframe formulations of each PCF type were studied and all products had similar nutrient concentrations to allow isolation of the effect of coating technology. Contrary to several studies, our data and model indicate that there is no significant difference in nutrient-release rates in water and a moist, solid substrate. This means that release rates determined in water can be used to model bio-available nutrient concentrations in moist soil or soilless media where sorption/desorption properties alter concentrations after release. Across all PCF, the nutrients most affected by temperature were typically N, K, B, Cu, and Zn, while the least affected were P, Mg, and Fe. We also found consistent differences among the coating technologies. Osmocote fertilizers released faster than specified at both high and low temperatures. Nutricote had relatively steady release rates over time and a nonlinear response to temperature. Polyon released more slowly than specified but replicate samples were highly uniform.

In temperate climates, annual bedding plant crops are typically produced in heated greenhouses from late winter through early summer. Temperature, photoperiod, light intensity, and transplant date are commonly manipulated during commercial production so that plants are in flower for predetermined market dates. We used nine flowering models that predict the effect of mean daily temperature on time from transplant until first flowering, which can be used to identify the combinations of transplant dates and growing temperatures necessary for flowering to occur on chosen market dates. The computer program Virtual Grower was also used to estimate greenhouse heating costs based on user-defined inputs such as building material, construction style, temperature set point, heating system, and typical weather at the selected locations. Using the flowering models and Virtual Grower, the temperatures and transplant dates that consumed the least amount of energy for heating, on a per-crop basis, were estimated for two market dates and three U.S. locations. For flowering on March 15, the estimated energy consumption for heating per crop decreased in Michigan as the greenhouse setpoint increased from 15 to 24°C for all species. In contrast, the temperature that elicited the lowest heating cost per crop in North Carolina for a March 15 finish date varied among species. This kind of analysis allows the determination of the most energy-efficient production schedule for greenhouse- and crop-specific situations.

Studies aimed at understanding Escherichia coli O157:H7 soil survival dynamics are paramount due to their inevitable introduction into the organic vegetable production systems via animal manure-based fertilizer. Therefore, a greenhouse study was conducted to determine the survival of E. coli O157:H7 in highly controlled soil matrices subjected to two variable environmental stressors: (1) soil volumetric water content (25 or 45 % VWC), and (2) the growth of clover (planted or unplanted). During the 7-week study, molecular-based qPCR analyses revealed that E. coli O157:H7 survival was significantly lower in soils maintained at either near water-holding capacity (45 % VWC) or under clover growth. The significant reduction under clover growth was only observed when E. coli populations were determined relative to all bacteria, indicating the need to further study the competition between E. coli O157:H7 and the total bacterial community in organic soils. Given the significant effect of clover on E. coli O157:H7 survival under different moisture conditions in this greenhouse-based study, this work highlights the antimicrobial potential of clover exudates in arable soils, and future work should concentrate on their specific mechanisms of inhibition; ultimately leading to the development of crop rotations/production systems to improve pre-harvest food safety and security in minimally processed, ready-to-eat and organic production systems.

Phosphorus (P) fertilization is frequently needed for profitable crop production. Modified Morgan P (MMP) is a soil test P used to estimate plant available P in soils. The critical values of MMP for P fertilization and maintenance recommendations are based on the P concentrations measured by a common colorimetric molybdenum blue method although other P quantification methods have also been used for MMP measurements. In this study, we collected 120 surface soil samples of Caribou Sandy loam under potato cultivation or its rotation crops from Maine, USA, and 72 soil samples of Cecil sandy loam with cotton/corn crops under conventional tillage and no-till management with chemical and poultry litter fertilization in Georgia, USA. The MMP levels in all 192 dry samples were greater when they were measured by an inductively coupled plasma (ICP)-based method, compared to the corresponding data produced from colorimetry. Our results show the two sets of data were positively and significantly correlated (r = 0.93, P –1 with standard deviation of 12.9, compared to the average of colorimetric MMP level of 14.9 mg P kg–1 with standard deviation of 8.8. Based on the observations in this work, both colorimetric and ICP-based methods can be used for P fertilizer recommendation, but a conversion factor should be applied for ICP data as the current recommendation systems are based on colorimetric M&R data.

Greenhouses that are well sealed can result in carbon dioxide (CO2) drawdown and suppressed plant growth. While growers can add supplemental CO2, it is unknown how supplemental CO2 fits within the framework of sustainable crop production in greenhouses. In this study, supplemental CO2 was used in combination with reduced temperatures to evaluate the productivity of ‘Grand Rapids’ lettuce (Latuca sativa) compared with a traditionally maintained, warmer, and well-insulated greenhouse without supplemental CO2 at a commercial facility. Simulations using Virtual Grower software based on identical greenhouses compared fuel use and carbon (C) consumed because of heating and CO2 supplementation. Models were verified with measurements in a well-sealed commercial greenhouse; CO2 quickly decreased to below 300 ppm in a nonsupplemented greenhouse containing plants. Supplemental CO2 boosted total leaf number and mass of lettuce even though temperatures were maintained 3 °F lower in elevated CO2 than in the traditional management scenario. Maintaining a cooler greenhouse but adding CO2 decreased total carbon (C) consumed (by combined fuel use and CO2 supplementation) by 7% during the 3-month season that required a well-sealed greenhouse. Additionally, fuel savings because of lower temperature set points paid for the cost of adding CO2. The use of CO2 enrichment should be considered as a tool in sustainable systems when its use can counteract the plant growth and development reductions brought on by lowered temperatures.

The use of copper (Cu) in agriculture is widespread as a pesticide, and it is present in high concentrations in certain types of manures. As the use of Cu continues and manure management is incorporated into sustainable systems, the likelihood of Cu toxicity increases. Supplemental silicon has been used to successfully counteract potential micronutrient toxicity. There is currently considerable debate regarding the value of including silicon (Si) as a nutrient in fertility programs and as such, it is not part of a typical management practice in floriculture crop production in the United States. We investigated the potential for Si to ameliorate the effects of Cu toxicity in both a Si-accumulating [zinnia (Zinnia elegans)] and a Si-non-accumulating [snapdragon (Antirrhinum majus)] species. Using visible stress indicators and dry weight analysis, it initially appeared that Si was a significant benefit to only zinnia under Cu toxicity. Enzymatic assays and elemental analysis of leaves, stems, and roots revealed that both species responded to supplemental Si, showing evidence of reduced stress and nutrient concentrations more similar to healthy, control plants than plants exposed to Cu toxicity. Although there appear to be differences in the extent of Si-mediated amelioration of Cu toxicity between these two plants, both responded to supplemental Si. This adds to the growing body of evidence that all plants likely have Si-mediated responses to stress, and its inclusion into fertility programs should be more broadly considered than current practices.

Aim Effects of elevated CO2 on N relations are well studied, but effects on other nutrients, especially micronutrients, are not. We investigated effects of elevated CO2 on response to variation in boron (B) availability in three unrelated species: seed geranium (Pelargonium x hortorum), barley (Hordeum vulgare), and water fern (Azolla caroliniana).

Clerodendrum thomsoniae plants were grown in silica sand culture to induce and photograph nutritional disorder symptoms. Plants were grown with a complete modified Hoagland's all nitrate solution. The nutrient deficiency treatments were induced with a complete nutrient formula minus one of the nutrients. Boron toxicity was also induced by increasing the element ten times higher than the complete nutrient formula. Reagent grade chemicals and deionized water of 18-mega ohms purity were used to formulate treatment solutions. The plants were automatically irrigated and the solution drained from the bottom of the pot and captured for reuse. The nutrient solutions were completely replaced weekly. Plants were monitored daily to document and photograph sequential series of symptoms as they developed. Typical symptomology of nutrient disorders and critical tissue concentrations are presented. Plants were harvested for nutrient analysis when initial symptoms were expressed. Nutrient deficiency symptoms were describ...

Dairy cow manure compost (DMC) was evaluated as a soilless substrate substitute for dolomitic limestone and peat moss in two experiments. The objectives were 1) to quantify the impact of DMC on substrate pH establishment and stabilization throughout crop time and 2) to test the effect of DMC on physical properties of substrate. Peat moss plus DMC (at 5 to 30% by volume) was held constant at 75% volume and perlite at 25% without limestone. Two additional control treatments of 75% sphagnum peat moss and 25% perlite were formulated with and without agricultural dolomitic limestone. Pot chrysanthemum ‘Kory’ plants were transplanted into 16.5-cm diameter (1.4 L) plastic pots and fertilized at each irrigation with 17N-2.2P-14.1K neutral fertilizer. Additions of 0 to 30% DMC resulted in initial substrate pH levels of 3.1 to 6.5. Although pH declined during plant production, the decline was similar in the agricultural limestone and the 20 to 30% DMC treatments that had similar initial pH levels. Thus, pH buffering capacity of DMC was similar to the limestone. The initial EC levels for all substrates were within the acceptable range for seedlings and bedding plants. Magnitude of shrinkage did not relate to addition of DMC and was of little commercial significance. Irrespective of time in the cropping cycle, DMC resulted in increased dry bulk density (Db), decreased total porosity (TP) and container capacity (CC), and little effect on air space (AS). AS levels were in a good range of 15% and above for the 7.6 cm tall test cylinders. End of crop tissue analysis indicated that DMC resulted in higher leaf concentrations of potassium, sulfur, copper, iron, and manganese, lower, but adequate, calcium and magnesium, and similar nitrogen, phosphorus, boron, and zinc concentrations. Maximum plant growth (dry weight) occurred with 15% DMC in Experiment 1 and with 10% DMC in Experiment 2. All limestone and a portion of peat moss were effectively replaced with DMC.

Fuel prices have fluctuated wildly in the last several years, and faced with unpredictable or rising fuel costs, growers often lower temperature set points to decrease fuel use. However, plant growth and development are influenced by lower temperatures and may actually cause increases in fuel use as a result of longer production times. Alternative strategies to efficient crop production are needed. Fertility, light, and CO2 are other environmental factors that can be manipulated within a greenhouse but how all three interact together on growth and development are surprisingly not well known. Petunia ×hybrida Vilm. were grown in controlled environments in a 2 × 2 × 2 factorial study investigating how light, fertility, and CO2 influence growth and development, including shoot partitioning, nutrient uptake, and carbohydrate concentration. Generally, light enhanced flowering, both mass and fraction of total biomass, whereas increased fertility was detrimental to the proportion of biomass allocated to flowers. The influence of CO2 was complex with high CO2 suppressing flowering and enhancing leaf growth, but only midway through the 7-week experiment. Carbohydrate concentration remained high in elevated CO2, even when light and fertility were not limiting. This suggests a sink limitation, so even in high light and fertility, crop response to enhanced CO2 was low. Although CO2 had no size effect late in growth, CO2 suppressed nutrient concentrations. Together, these data suggest strategies that growers may have in controlling their crop growth and development and indicate that enhanced growth (leaf and steam mass) may be at the detriment of development (flowering mass and allocation).

Greenhouses are used in many climates for season extension or year-round production and can be expensive to heat. Greenhouse users and growers are often faced with management decisions that rely on an understanding of how temperature settings, heating systems, fuel types, and construction decisions influence overall heating costs. There are no easy-to-use programs to calculate heating costs associated with these factors over full cropping seasons. A computer program called Virtual Grower was created that helps calculate heating costs at many U.S. sites. The program uses a weather database of typical hourly temperature, light, and wind information of 230 sites from the National Renewable Energy Laboratory in the calculations. A user can define unique design characteristics such as building material and construction style. The user also defines the type of heating system and heating schedule, and then the program will predict heating costs based on typical weather at the selected location. Shorter-term predictions with weather forecasts of 2 days or less can be made with the software if there is an internet connection through integration with local weather forecasts. Virtual Grower can serve as a platform from which many other features can be added, such as plant growth and scheduling. Continued development will improve the software and allow users to perform baseline analysis of their heating costs, identify areas in their production to improve efficiency, and take some of the guesswork out of energy analysis in unique greenhouses.

Polyacrylamide (PAAm) hydrogels are commonly employed to ensure soil hydration in horticulture, but studies have shown that they have a minimal effect on crop life and quality. The reasons for this poor performance are not understood since the commercial hydrogels have not been adequately characterized. PAAm hydrogels were synthesized and their properties were measured along with those of commercial hydrogels. Hydrogel swelling, density, and SEM analyses showed that the commercial hydrogels were most likely a derivative of PAAm with ionic groups and they were able to retain moisture for only a few hours.

Pansy (Viola ×wittrockiana Gams.), petunia (Petunia ×hybrida hort. Vilm.), and gerbera daisy (Gerbera jamesonii Bol. ex Adlam.) plants were grown hydroponically to characterize the deficiency symptoms caused by the absence of calcium (Ca) or boron (B). Primary symptoms occurred on the youngest tissue for both elements, but distinct differences between Ca and B deficiencies were observed. Plants responding to Ca deficiency exhibited discoloration and upward rolling of leaves and ultimately necrosis. Plants responding to B deficiency exhibited minor chlorosis, upward curling, and thickening of leaves, distorted meristems, and strap-like leaves. A second experiment investigated how a temporary disruption of Ca or B affects the plant throughout the crop cycle. Either Ca or B was removed from the nutrient solution for a 7-day period from Day 15 to Day 21, Day 22 to Day 28, or Day 29 to Day 35 after sowing. After the 7-day disruption, the respective element was reintroduced to the plants. Regardless of when the plants were deprived of Ca or B, the symptoms of the respective deficiency were present at the end of the experiment. These studies have shown that a temporary disruption of either Ca or B can cause lasting symptoms throughout the plug production cycle. Also, the symptoms that have been observed in plug production were most similar to those symptoms caused by B deficiency, not Ca deficiency.

Apart from a role in cell wall structure, specific functions for boron (B) in plants are unclear; hence, responses and adaptations to B stress are incompletely understood. We tested hypotheses that net photosynthesis (Pn) decreases with B deficiency before visible foliar symptoms and that higher nonphotoinhibitory light levels enhance soluble carbohydrate status and therefore mitigate B deficiency. Geranium (Pelargonium ×hortorum L.H. Bailey cv. Nittany Lion Red) plants were grown hydroponically and were then exposed to normal (45 μm) or deficient (0 μm) B at two light levels [100 or 300 μmol·m−2·s−1 photosynthetically active radiation (PAR)]. Photosynthesis [net CO2 uptake, carboxylation, and photosystem II (PSII) efficiency] was monitored for 5 days, as were concentrations of B, chlorophyll, soluble sugars, total protein, and several photosynthetic and stress proteins [ribulose 1,5-bisphospate carboxylase oxygenase (rubisco), rubisco activase, oxygen-evolving complex-23 (OEC23), Cu/Zn-superoxide dismutase (SOD), Mn-SOD, and eukaryotic translation initiation factor 5A-2 (eIF5A-2)]. Biomass and sugar concentration were greater in high light, and mass was decreased by B deficiency only in leaves in high light. Boron deficiency decreased [B] in all tissues, especially in new leaves. Carboxylation efficiency and Pn decreased within 1 day of B deficiency in low light, but not until 5 days in high light. Chlorophyll concentration decreased, and Mn-SOD increased transiently, with B deficiency in both light levels, but no other effects of low B were observed. Protection of Pn by higher light was confirmed in a different cultivar (Maverick White) grown at 100, 300, and 500 μmol·m−2·s−1 PAR. Thus, in geranium, photosynthesis is affected by B deficiency before effects on leaf growth, and higher light can at least temporarily ameliorate B deficiency, perhaps partly due to enhanced carbohydrate status.

Humans are increasing atmospheric CO2, ground-level ozone (O3), and mean and acute high temperatures. Laboratory studies show that elevated CO2 can increase thermotolerance of photosynthesis in C3 plants. O3-related oxidative stress may offset benefits of elevated CO2 during heat-waves. We determined effects of elevated CO2 and O3 on leaf thermotolerance of field-grown Glycine max (soybean, C3). Photosynthetic electron transport (et) was measured in attached leaves heated in situ and detached leaves heated under ambient CO2 and O3. Heating decreased et ,w hich O3 exacerbated. Elevated CO2 prevented O3-related decreases during heating, but only increased et under ambient O3 in the field. Heating decreased chlorophyll and carotenoids, especially under elevated CO2. Neither CO2 nor O3 affected heat-shock proteins. Heating increased catalase (except in high O3) and Cu/Zn-superoxide dismutase (SOD), but not Mn- SOD; CO2 and O3 decreased catalase but neither SOD. Soluble carbohydrates were unaffected by heating, but increased in elevated CO2. Thus, protection of photosynthesis during heat stress by elevated CO2 occurs in field-grown soybean under ambient O3, as in the lab, and high CO2 limits heat damage under elevated O3, but this protection is likely from decreased photorespiration and stomatal conductance rather than production of heat-stress adaptations.

Silicon (Si) detection, distribution, and quantification in plants was compared using electron beam analysis (EBA; scanning electron microscopy coupled with energy dispersive X‐ray analysis), colorimetric analysis, and inductively coupled plasma–optical emission spectroscopy (ICP‐OES) in 14 economically important floriculture species. Using EBA, Si was identified most commonly around the base of trichomes and along the leaf margins. The ICP‐OES processing and analysis for Si using sodium hydroxide (NaOH) resulted in damaged torches and microwavable Teflon® vessels that required expensive replacement at the end of each run, but this was not the case in the colorimetric method or with a potassium hydroxide (KOH)–based matrix in the ICP‐OES. The results of these analyses suggest there is agreement between quantification methods, and EBA has a lower detection limit of about 300 mg kg−1 dry weight of Si. Several new floriculture species (zinnia, impatiens, verbena, and calibrachoa) were identified that take up...

Copper (Cu) is an essential micronutrient for plants and is the a.i. in pesticides for some pathogens and algae. Elevated doses of Cu can cause toxicity in plants. While silicon (Si) is reported to alleviate the toxicity of some heavy metals, its role in reducing the symptoms induced by excess Cu is unclear. Therefore, the role of Si in plant response to Cu stress was investigated in arabidopsis [Arabidopsis thaliana (L.) Heyn.]. Based on plant symptoms (a reduction of leaf chlorosis as well as increased shoot and root biomass) and a reduction of phenylalanine ammonia lyase [PAL (EC 4.3.1.5), a stress-induced enzyme] activity in the shoot, Si was found to alleviate copper stress. Real-time reverse transcriptase-polymerase chain reaction analyses indicated that the RNA levels of two arabidopsis copper transporter genes, copper transporter 1 (COPT1) and heavy metal ATPase subunit 5 (HMA5) were induced by high levels of Cu, but were significantly decreased when Si levels were also elevated. Taken together, our findings indicate that Si addition can improve the resistance of arabidopsis to Cu stress, and this improvement operates on multiple levels, ranging from physiological changes to alterations of gene expression.

Sudden pH decline (SPD) describes the situation where crops growing at an appropriate pH rapidly (within 1–2 weeks) cause the substrate pH to shift downward one to two units. ‘Designer Dark Red’ geraniums (Pelargonium ×hortorum Bailey) were grown in three experiments to assess possible effects of light on SPD and phosphorous (P) uptake. The first experiment tested the effect of four light intensities (105, 210, 575, and 1020 ± 25 μmol·m−2·s−1) on substrate acidification. At 63 days, substrate pH declined from 6.0 to 4.8 as light intensity increased. Tissue P of plants grown at the highest two light levels was extremely low (0.10%–0.14% of dry weight). P stress has been reported to cause acidification. Because plants in the two lowest light treatments had adequate P, it was not possible to determine if the drop in substrate pH was a direct light effect or a combination of light and P. The second experiment used a factorial combination of the three highest light levels from Expt. 1 and five preplant P rates (0, 0.065, 0.13, 0.26, or 0.52 g·L−1 substrate) to assess this question. When tissue P concentrations were deficient, pH decreased by 0.6 to 1.0 pH units within 2 weeks and deficiency occurred more often with high light intensity. These data indicated that P deficiency caused substrate acidification and indicated the possibility that P uptake was suppressed by high light intensity. The third experiment was conducted in hydroponics to determine the direct effect of high light intensity on P uptake. In this experiment, cumulative P uptake per gram root and the rate of P uptake per gram root per day both decreased 20% when light intensity increased from 500 to 1100 μmol·m−2·s−1. It is clear from this study that P deficiency causes geraniums to acidify the substrate and that high light suppresses P uptake.

Sudden pH decline (SPD) describes the situation where crops growing at an appropriate pH rapidly (within 1–2 weeks) cause the substrate pH to shift downward one to two units. ‘Designer Dark Red’ geraniums (Pelargonium ×hortorum Bailey) were grown in three experiments to assess possible effects of temperature on SPD. The first experiment tested the effect of four day/night temperature regimes (14 °C day/10 °C night, 18 °C day/14 °C night, 22 °C day/18 °C night, and 26 °C day/22 °C night) on substrate acidification. At 63 days after transplanting (DAT), substrate pH declined from 6.8 to 4.6 as temperature increased. Tissue phosphorus (P) of plants grown at the highest three temperatures was extremely low (0.10%–0.14% of dry weight), and P stress has been reported to cause acidification. It was not possible to determine if the drop in substrate pH was a singular temperature effect or a combination of high temperature and low P. To resolve this, a second experiment tested a factorial combination of the three highest temperatures from the first experiment and five preplant P rates (0, 0.065, 0.13, 0.26, or 0.52 g·L−1 substrate). Regardless of tissue P concentrations, which ranged from deficient to above adequate, substrate pH decreased with increasing temperature. At 63 DAT, in the 0.065 and 0.13 P treatments, tissue P was deficient and pH decreased with increasing temperature from 5.6 to 4.7 and 5.9 to 4.7, respectively. In the 0.26 P treatment, tissue P was adequate at the lowest temperature and there was no acidification. At the mid- and highest temperatures, tissue P was deficient and statistically equivalent, yet pH decreased to 5.2 and 4.7, respectively. In the highest P treatment, tissue P levels were unaffected by temperature, above adequate, and pH declined with each increase in temperature from 6.5 to 5.0. The results at 63 DAT once more showed that temperature acted independent of tissue P and caused geraniums to acidify the substrate. In the third experiment, the amount of acidity produced by roots of plants grown at the two highest temperatures used in the first two experiments was quantified. Plants grown at the higher temperature produced 28% more acid per gram dry root. The results herein indicate that high temperature can induce SPD by geranium.

Arsenic (As) contamination is widespread in the industrial areas of northwest Ohio. Plant species that both take up As and are appropriate for the climate and growth conditions of the region are needed for phytoremediation to be successfully employed. Actively growing plants from 22 species of native genera were exposed to As in hydroponics systems (either 0, 10, or 50 mg As L−1; 1 week) and commercially available potting mix (either 0, 10, 25, 100, or 250 mg As L−1; 2 weeks), depending on their growth conditions. Aboveground plant tissues were harvested and digested, and concentrations of As were determined by inductively coupled plasma–optical emission spectrometry. The highest tissue concentrations of As (mg As kg−1 dw) were recorded in seven plant species: Rudbeckia hirta (661), Helenium autumnale (363 in tissues formed after exposure to As), Lupinus perennis (333), Echinacea purpurea (298), Coreopsis lanceolata (258), Lepidium virginicum (214), and Linum lewisii (214). These seven species ar...

Unique growing containers and nontraditional types of plant presentation may lead to new production problems for growers. This study was conducted to evaluate the growth of a popular container plant, calibrachoa (Calibrachoa ×hybrida), produced in hanging flower pouches using different growing substrate compositions, polymer amendments, and the layering of substrate types of differing moisture holding capacity with the goal of achieving more uniform plant growth and improved after-sale maintenance. Plastic cylindrical hanging pouches were filled with one of nine hydrated substrate types or combinations. Rooted cuttings of ‘Colorburst Violet’ calibrachoa were planted as indicator plants to identify treatment effects because of their susceptibility to iron deficiency-induced chlorosis of new leaves. Daily measurements of substrate moisture were taken to determine the need for irrigation. Chlorophyll content was estimated nondestructively with a hand-held chlorophyll meter to determine the impact of moisture content. Light, porous substrates resulted in the most uniformly green plants and high numbers of flowers from top to bottom. A layered pouch with heavy, compost-amended substrate above a light, porous layer also produced high-quality, uniform plants. This enabled water to be distributed more uniformly throughout the container volume. This study provides fundamental information on how container geometry and soil moisture retention can influence water management decisions by the grower.

Plant performance and appearance in deficient and toxic levels of nutrients are well characterized. However, less is known about the potential subtleties of plant growth, form, development, nutrient uptake, and biotic stress tolerance in the broad tolerable range. Begonia [Beg (Begonia × tuberhybrida Voss)] and new guinea impatiens [NGI (Impatiens hawkeri Bull.)] were grown over a wide range of N (from 1.78 to 57.1 mm NH4:NO3 ratio at a 1:1 ratio supplied as nutrient solution) in a peat:perlite soilless substrate in greenhouse conditions. Plant growth, development, chlorophyll content, leaf angle, nutrient uptake, tissue caloric value, and susceptibility to Botrytis cinerea Pers.:Fr. disease were evaluated in two experiments. Elevated N supply resulted in decreased plant height (16% in Beg and 7% to 16% in NGI), flower count (3% to 48% in Beg and 7% to 49% in NGI), bud numbers (23% to 80% in Beg), canopy area (11% to 33% in NGI), and mass (21% to 33% in Beg and 18% to 58% in NGI). Chlorophyll content saturated at an N supply of 28.6 mm. N uptake efficiency, shoot N use efficiency, and shoot N utilization efficiency decreased with increasing N supply. Elevated levels of N supply from 7.15 to 57.1 mm also increased the susceptibility of Beg to B. cinerea disease by 10% to 80% in stems and 3% to 14% in leaves. The increase in susceptibility also corresponded with increased tissue energy content (kJ·g−1) and altered leaf orientation. This study indicates many plant changes occur between nutrient extremes that can have a significant impact on growth, development, and the ability to withstand disease.

Cumulative absorbed radiation is highly correlated with crop biomass and yield. In this chapter we describe the use of a digital camera and commercial imaging software for estimating daily radiation capture, canopy photosynthesis, and relative growth rate. Digital images were used to determine percentage of ground cover of lettuce (Lactuca sativa L.) communities grown at five temperatures. Plants were grown in a steady-state, 10-chamber CO2 gas exchange system, which was used to measure canopy photosynthesis and daily carbon gain. Daily measurements of percentage of ground cover were highly correlated with daily measurements of both absorbed radiation (r(sup 2) = 0.99) and daily carbon gain (r(sup 2) = 0.99). Differences among temperature treatments indicated that these relationships were influenced by leaf angle, leaf area index, and chlorophyll content. An analysis of the daily images also provided good estimates of relative growth rates, which were verified by gas exchange measurements of daily carbon gain. In a separate study we found that images taken at hourly intervals were effective for monitoring real-time growth. Our data suggests that hourly images can be used for early detection of plant stress. Applications, limitations, and potential errors are discussed. We have long known that crop yield is determined by the efficiency of four component processes: (i) radiation capture, (ii) quantum yield, (iii) carbon use efficiency, and (iv) carbon partitioning efficiency (Charles-Edwards, 1982; Penning de Vries & van Laar, 1982; Thornley, 1976). More than one-half century ago, Watson (1947, 1952) showed that variation in radiation capture accounted for almost all of the variation in yield between sites in temperate regions, because the three other components are relatively constant when the crop is not severely stressed. More recently, Monteith (1977) reviewed the literature on the close correlation between radiation capture and yield. Bugbee and Monje (1992) demonstrated the close relationship between absorbed radiation and yield in an optimal environment.

An appropriate blend of growing media components increases water holding capacity and reduces irrigation frequency. Synthetic commercial materials, referred to as hydrogels, have remarkable hydrating properties, but can add significantly (about 15%) to the cost of growing media. The literature generally states that the physical characteristics of hydrogels, such as polyacrylamide (PAM), are altered by the presence of divalent cations (Ca2+ and Mg2+). Few studies, however, have simultaneously investigated plant growth and development and media characteristics on a daily basis throughout plant production. Thus, the mechanisms explaining the reported beneficial and/or detrimental effects from PAM incorporation remain hidden. In this study, canopy ground cover of two species [pansy (Viola ×wittrockiana Gams) and new guinea impatiens (Impatiens hawkeri Bull)] was measured daily, from transplanting to marketable size, using digital imaging to determine growth differences of plants grown in media containing different amounts of PAM. Media water content was determined with time-domain reflectance probes every 10 minutes in media treatments. Total number of irrigation events, time between irrigation events, root development after 4 and 8 weeks of growth, flower number, flower longevity, and dry masses of the shoot were also measured. Scanning electron microscopy revealed significant structural differences in hydrated PAM depending on water quality. The pansy canopy coverage was significantly greater with hydrogels, and root growth early in production was enhanced with PAM. No such effect was observed for new guinea impatiens. Total flower numbers and flower longevity of new guinea impatiens decreased with increasing amount of PAM (16.7% or higher) in the media. PAM incorporation reduced the need for irrigation early in production for both species, but by the end of production, those new guinea impatiens plants were smaller (less shoot dry mass) and required irrigation as often as plants grown without PAM. This effect coincided with reduced media volume, air capacity, and total porosity in PAM-containing media. Theoretical analysis of the potential benefits from hydrogels confirms the potential benefit early in production with little to no benefit later in production and in post-production. These data will assist growers in determining if the benefits derived from the use of PAM justify the added cost of medium.

Cloudy days cause an abrupt reduction in daily photosynthetic photon flux (PPF), but we have a poor understanding of how plants acclimate to this change. We used a unique 10-chamber, steady-state, gas-exchange system to continuously measure daily photosynthesis and night respiration of populations of a starch accumulator [tomato (Lycopersicon esculentum Mill. cv. Micro-Tina)] and a sucrose accumulator [lettuce (Lactuca sativa L. cv. Grand Rapids)] over 42 days. All measurements were done at elevated CO2 (1200 μmol·mol-1) to avoid any CO2 limitations and included both shoots and roots. We integrated photosynthesis and respiration measurements separately to determine daily net carbon gain and carbon use efficiency (CUE) as the ratio of daily net C gain to total day-time C fixed over the 42-day period. After 16 to 20 days of growth in constant PPF, plants in some chambers were subjected to an abrupt PPF reduction to simulate shade or a series of cloudy days. The immediate effect and the long term acclimation rate were assessed from canopy quantum yield and carbon use efficiency. The effect of shade on carbon use efficiency and acclimation was much slower than predicted by widely used growth models. It took 12 days for tomato populations to recover their original CUE and lettuce CUE never completely acclimated. Tomatoes, the starch accumulator, acclimated to low light more rapidly than lettuce, the sucrose accumulator. Plant growth models should be modified to include the photosynthesis/respiration imbalance and resulting inefficiency of carbon gain associated with changing PPF conditions on cloudy days.

High relative humidity (RH) can cause lower concentrations of boron (B) accumulating in plants. The common greenhouse practice of controlling excess temperatures by applying mist irrigation to young plants (plugs) can result in elevated RH levels, especially with plugs grown in high heat and humidity conditions of summer. ‘Dynamite Yellow’ pansy (Viola ×wittrockiana Gams.), ‘White Storm’ petunia (Petunia ×hybrida Vilm.), and ‘Festival Apricot’ gerbera (Gerbera jamesonii Bolus) plugs were grown in high or ambient RH conditions to determine the effect RH had on B uptake. Results indicate that an increase in RH decreased the amount of water the plant lost as a result of transpiration resulting in lower concentrations of B in shoot tissue. Boron concentrations in leaf tissue were 9.43, 10.56, and 17.81 mg·L−1 in pansy, petunia, and gerbera plants, respectively, grown in high RH conditions. These values were significantly lower than pansy, petunia, and gerbera plants grown in ambient RH conditions (19.94, 25.49, and 42.71 mg·L−1, respectively). Leaf distortion, consistent with B deficiency symptoms, was present in petunia and gerbera plants. Similar trends were observed when the experiment was repeated and leaf distortion was present in all species. This provides convincing evidence that the distorted growth observed in pansy, petunia, and gerbera plug production is the result of limited B caused by excessive humidity.

Rice (Oryza sativa L.) is a useful model crop plant. Rice was the first crop plant to have its complete genome sequenced. Unfortunately, even semi-dwarf rice cultivars are 60 to 90 an tail, and large plant populations cannot be grown in the confined volumes of greenhouses and growth chambers. We recently identified an extremely short (20 em tall) rice line, which is an ideal model for larger rice cultivars. We called this line "Super Dwarf rice." Here we report the response of Super Dwarf to temperature, photoperiod, photosynthetic photon flux (PPF), and factors that can affect time to head emergence. Vegetative biomass increased 6% per degree Celsius, with increasing temperature from 27 to 31 C. Seed yield decreased by 2% per degree Celsius rise in temperature, and as a result, harvest index decreased from 60 to 54%. The time to heading increased by 2 d for every hour above a 12-h photoperiod. Yield increased with increasing PPF up to the highest level tested at 1800 micro-mol/sq m/s (12-h photoperiod; 77.8 mol/sq m/d). Yield efficiency (grams per mole of photons) increased to 900 micro-mol/sq m/s and then slightly decreased at 1800 micro-mol/sq m/s . Heading was delayed by addition of gibberellic acid 3 (GA,) to the root zone but was hastened under mild N stress. Overall, short stature, high yield, high harvest index, and no extraordinary environmental requirements make Super Dwarf rice an excellent model plant for yield studies in controlled environments.

Background and aims Carbon gain depends on efficient photosynthesis and adequate respiration. The effect of temperature on photosynthetic efficiency is well understood. In contrast, the temperature response of respiration is based almost entirely on short-term (hours) measurements in mature organisms to develop Q(10) values for maintenance and whole-plant respiration. These Q(10) values are then used to extrapolate across whole life cycles to predict the influence of temperature on plant growth. Methods In this study, night temperature in young, rapidly growing plant communities was altered from 17 to 34 degrees C for up to 20 d. Day temperature was maintained at 25 degrees C. CO(2) gas-exchange was continuously monitored in ten separate chambers to quantify the effect of night-temperature on respiration, photosynthesis and the efficiency of carbon gain (carbon use efficiency). Key results Respiration increased only 20-46 % for each 10 degrees C rise in temperature (total respiratory Q(10) of between 1.2 to about 1.5). This change resulted in only a 2-12 % change in carbon use efficiency, and there was no effect on cumulative carbon gain or dry mass. No acclimation of respiration was observed after 20 d of treatment. Conclusions These findings indicate that whole-plant respiration of rapidly growing plants has a small sensitivity to temperature, and that the sensitivity does not change among the species tested, even after 20 d of treatment. Finally, the results support respiration models that separate respiration into growth and maintenance components.

The productivity of lettuce in a combination of high light, high temperature, and elevated CO2 has not been commonly studied because rapid growth usually causes a calcium deficiency in meristems called tipburn, which greatly reduces quality and marketability. We eliminated tipburn by blowing air directly onto the meristem, which allowed us to increase the photosynthetic photon flux (PPF) to 1000 μmol·m-2·s-1 (57.6 mol·m-2·d-1); two to three times higher than normally used for lettuce. Eliminating tipburn doubled edible yield at the highest PPF level. In addition to high PPF, CO2 was elevated to 1200 μmol·m-2·mol-1, which increased the temperature optimum from 25 to 30 °C. The higher temperature increased leaf expansion rate, which improved radiation capture and more than doubled yield. Photosynthetic efficiency, measured as canopy quantum yield in a whole-plant gas exchange system, steadily increased up to the highest temperature of 32 °C in high CO2. The highest productivity was 19 g·m-2·d-1 of dry biomass (380 g·d-1 fresh mass) averaged over the 23 days the plants received light. Without the limitation of tipburn, the combination of high PPF, high temperature, and elevated CO2 resulted in a 4-fold increase in growth rate over productivity in conventional environments.

Dwarf plants are useful in research because multiple plants can be grown in a small area. Rice (Oryza sativa L.) is especially important since its relatively simple genome has recently been sequenced. We are characterizing a gibberellic acid (GA) mutant of rice (japonica cv 'Shiokari,' line N-71) that is extremely dwarf (20 cm tall). Unfortunately, this GA mutation is associated with poor germination (70%) under aerobic conditions. Neither exogenous GA nor a dormancy-breaking heat treatment improved germination. However, 95% germination was achieved by germinating the seeds anaerobically, either in a pure N2 environment or submerged in unstirred tap water. The anaerobic conditions appear to break a mild post-harvest dormancy in this rice cultivar. Copyright 2002 Crop Science Society of America.

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.

Traditional overhead lighting of dense crop stands in controlled environments favors development of upper leaf layers to maximize interception of light incident at the top of the foliar canopy. The resultant mutual shading of lower leaves in the understory of the canopy can severely limit productivity and yield of planophile crops. Intracanopy lighting alleviated the effects of mutual shading in dense, vegetative stands of cowpea [Vigna unguiculata (L.) Walp ssp. unguiculata] growing in a controlled environment by sustaining irradiance within the understory throughout development of this edible-foliage crop. For an overhead lighting system, photosynthetic photon flux (PPF) in the understory was reduced to 1% of its initial value by 35 days of growth. PPF in an intracanopy-lighted stand remained within 30 μmol·m-2·s-1 of initial values throughout the 50-day cropping period. Spectral distribution of radiation within the intracanopy-lighted stand also remained relatively constant throughout canopy development. In the overhead-lighted stand, violet and blue radiation in the understory decreased as much as 60% from initial values. Stability of the radiation environment within the intracanopy-lighted stand delayed leaf senescence 27 days beyond when interior leaves of the overhead-lighted canopy began to turn yellow on day 16. The intracanopy-lighted stand produced twice as much edible biomass per unit electrical energy consumed by lamps as for the overhead-lighted system. The treatment differences were due to the continuous presence of understory irradiation when using intracanopy lighting but not when using overhead lighting, and they underscore the importance of the entire foliar canopy in realizing the full productivity potential of dense crop stands in controlled environments.