Peat-based Medium Research Articles

Humic and Fulvic Acids Promote Growth and Flowering in Petunias at Low and Optimal Fertility

Humic substances are components of soil organic matter that influence soil structure and fertility. Humic and fulvic acids can be extracted from soil and other organic sources, and are used as biostimulants to promote plant growth and increase nutrient availability and uptake. The goal of this study was to determine whether selected humic and fulvic acid–based commercial products would promote growth and flowering of petunia (Petunia ×hybrida) ‘Picobella Blue’ grown in soilless media with low or optimal fertilizer rates. Plants were grown in 11.4-cm pots filled with peat-based media [80:20 peat:perlite (v/v); pH 5.4]. Three biostimulant products were evaluated at different rates and application frequencies: Huma Pro, a liquid humic acid biostimulant; Fulvi Pro, a liquid fulvic acid biostimulant; and Micromate, a powder containing both humic and fulvic acids. In Expt. 1, Huma Pro and Fulvi Pro were drenched weekly onto the growing media at a rate of 5, 10, or 20 mL⋅L–1; Micromate was drenched weekly at a rate of 5, 10, 20, or 40 g⋅L–1. Plants were fertilized with either 50 mg⋅L–1 nitrogen (N) (low fertility) or 100 mg⋅L–1 N (optimal fertility) from Jack’s Professional 20N–1.3P–15.7K Petunia FeED each irrigation. Control plants received fertilizer but no biostimulant treatments. In Expt. 2, biostimulant treatments were drenched once at transplant, biweekly, or weekly at a rate of 1.25, 2.5, 5, or 10 mL⋅L–1 for Huma Pro and Fulvi Pro; and at 5, 10, 20, or 40 g⋅L–1 for Micromate. All plants received constant liquid feed at the lower fertilizer rate of 50 mg⋅L–1 N. In Expt. 1, plants fertilized with 100 mg⋅L–1 N and treated with 20 g⋅L–1 Micromate had the best performance. The average shoot dry weight was 32% greater than that of the control plants. Micromate (20 g⋅L–1)-treated plants had an average of five more flowers per plant, and they flowered 4 days earlier than untreated control plants. In Expt. 2, plants treated with 40 g⋅L–1 of Micromate weekly had the greatest shoot dry weight compared with the other treatments. Weekly Micromate treatments (40 g⋅L–1) resulted in plants with an average of 13 more flowers per plant, which flowered 7 days earlier than control plants. Plants treated with Fulvi Pro and Huma Pro at 20 mL⋅L–1 had a significantly greater concentration of potassium in shoot tissue, whereas Micromate treatments at 20 and 40 g⋅L–1 resulted in a greater concentration of phosphorous in the shoots. The humic and fulvic acids in Micromate improved petunia crop quality by promoting vegetative growth, increasing flower numbers, and reducing the time to flower.

Dissolution of Silicon from Soilless Substrates and Additives

Silicon (Si) is a beneficial element that is usually ample in mineral soil solution, but it is minimally bioavailable from soilless substrates. Several Si additives are commercially available, but the rate of dissolution of Si is not well-characterized. The ideal additive would steadily release bioavailable Si over the crop lifecycle. We report the long-term (120 days) dissolution of Si from soilless substrates and substrate additives. Studies involving gently agitated containers with deionized water indicated that perlite, sphagnum peat, vermiculite, and coconut coir released less than 0.03 mmol Si per liter of substrate per day. Rice hulls and wollastonite (CaSiO3) had 7- to 130-times faster rates of dissolution in this system; therefore, they were further studied in peat-based media. Dissolution of Si from the addition of 1 g wollastonite per liter of peat peaked at day 10 at 2.1 mmol Si per liter of media per leaching event (15% by volume); then, it gradually decreased over 120 days. The peak dissolution of Si amended with 12% rice hulls was similar, but it gradually increased over time. The concentrations of nine heavy metals in plant tissue were compared with untreated control plants to determine wollastonite and steel slag. The concentration of some elements statistically increased, but all concentrations were well below the legal concentration limits of these elements for human consumption in the United States. These results indicate that both wollastonite and rice hulls steadily release Si for up to 4 months; therefore, they are good sources of Si for container-grown crops in soilless media.

Compensation of adverse growing media effects on plant growth and morphology by supplemental LED lighting.

There is an increasing interest in alternatives to peat in growing media due to environmental constraints. However, plants grown in peat substitutes often show impaired growth compared to plants grown in peat-based media. Hence, it would be interesting to know whether these deficiencies can be compensated by supplementing other growth factors, e.g. light. The present study aims to investigate the interactive nature between growing media and supplemental lighting on plant growth and morphology, and to examine whether supplemental light emitting diode (LED) lighting may compensate adverse growing media effects. Basil (Ocimum basilicum L.) and Chinese cabbage (Brassica rapa subsp. pekinensis) were grown in different growing media consisting of peat, green compost, coconut pulp, wood fibre, perlite and sphagnum moss under blue, red and far-red supplemental LED lighting. We found significant interactions between growing media and supplemental photosynthetically active radiation (PAR) on plant growth, morphology and development. At low light intensities, peat-based and substituted growing media performed similarly, whereas with increasing light intensities the peat-based growing media significantly outperformed their alternatives. The substrate choice determines the required amount of supplemental light to compensate for adverse growing media effects and the amount varies depending on plant species and season. Thereby, it was indicated that red light alleviates adverse growing media effects best. We also found that far-red light is not effective when background PAR is low and becomes more effective under high background PAR. The implications and prospects of the results are discussed.

Copper Can Be Elevated in Hydroponics and Peat-based Media for Potential Disease Suppression: Concentration Thresholds for Lettuce and Tomato

Copper (Cu) is typically adequate at 0.5 μM (0.03 ppm) in hydroponics and at 2 μM (0.125 ppm) in soilless media, but elevated levels can be used to inhibit pathogenic fungal growth. We studied the effect of elevated Cu on the growth of lettuce and tomato in peat-based media and deep-flow hydroponics. Lettuce growth in hydroponics was not hindered until a concentration greater than 4 μM (0.25 ppm) Cu was used, which is eight times greater than the adequate level. Tomato was more tolerant of elevated Cu, with no growth suppression up to 8 μM (0.5 ppm) in hydroponics. Organic matter tightly binds Cu, and bioavailability is thus determined by organic components in soilless media. We confirmed an adsorption capacity of 19 mg Cu per g of peat, which explains why there was no inhibition of lettuce or tomato growth up to 1000 μM (64 ppm) Cu in peat-based media. When chelated with ethylenediaminetetraacetic acid, Cu binding to organic matter was reduced and growth was decreased in lettuce but not tomato. Both species tolerated a 100-fold greater concentration of Cu in peat-based media than in deep-flow hydroponics. Elevated Cu in solution increased concentrations 20 times greater in root tissue than in leaves. These solution and tissue concentrations are greater than identified toxicity thresholds of pathogenic fungal and fungal-like organisms, and could thus be used to suppress root-borne fungal and fungal-like diseases.

Effect of hydroponic and peat-free media in transplant production of Rudbeckia hirta varieties under different photoperiodic lighting and their photosynthetic parameters

The purpose of this research was to determine the effects of varieties, different light conditions (short day, long day, natural short day with light pollution), and different growing media (perlite, peat-free, peat-based, aeroponics system) on Rudbeckia hirta plant production under controlled conditions (greenhouse). The morphological effects of each treatment (photoperiodic lightings and media) on different Rudbeckia varieties determined at 11 weeks-old ’Napfény’, ’Toto Gold’, ’Autumn Colors’, ’Prairie Sun’ and 16 weeks-old ’Napfény’. Plantlets received 12 hours daylight did not initiate flowers, remained stage of the leaf rosette in case of all varieties. The 14 hours light treatment in the aeroponics system and the same treatment in perlite and control (natural short day with 14 hours light pollution) plantlets had developed inflorescences or flower buds. The inflorescence axis of ‘Napfény’ was appeared at 13 weeks under long-day conditions, with 1.7 (perlite) - 2.7 (aeroponics) flower buds in 16 weeks. ’Toto Gold’, ’Autumn Colors’, ’Prairie Sun’ varieties developed inflorescences at 8 weeks, 14 hours aeroponics system resulted in the most of flower buds (’Toto Gold’: 6.5, ’Autumn Colors’: 3.25,’Prairie Sun’: 4.8 flower buds) at 11 weeks. Long daylight manipulation could be minimized crop times and achieved flowering potted plants at 11 weeks. The peat-based and peat-free media effect was observed on ‘Autumn Colors’. The number of leaves of peat-free ‘Autumn Colors’ transplants (16.8-20.3) was significantly higher than peat-based media (13.5-15.5). Other morphological parameters were not affected by the media treatments.

Identification of Plant Growth Promoting Rhizobacteria That Improve the Performance of Greenhouse-Grown Petunias under Low Fertility Conditions.

The production of greenhouse ornamentals relies on high fertilizer inputs to meet scheduling deadlines and quality standards, but overfertilization has negative environmental impacts. The goals of this study were to identify plant-growth-promoting rhizobacteria (PGPR) that can improve greenhouse ornamental crop performance with reduced fertilizer inputs, and to identify the best measurements of plant performance for assessing the beneficial impact of PGPR on ornamentals. A high-throughput greenhouse trial was used to identify 14 PGPR isolates that improved the flower/bud number and shoot dry weight of Petunia × hybrida ‘Picobella Blue’ grown under low fertility conditions in peat-based media. These 14 PGPR were then applied to petunias grown under low fertility conditions (25 mg L−1 N). PGPR-treated plants were compared to negative (untreated at 25 mg L−1 N) and positive (untreated at 50, 75, 100, and 150 mg L−1 N) controls. Multiple parameters were measured in the categories of flowering, vegetative growth, and vegetative quality to determine the best measurements to assess improvements in ornamental plant performance. Caballeronia zhejiangensis C7B12-treated plants performed better in almost all parameters and were comparable to untreated plants fertilized with 50 mg L−1 N. Genomic analysis identified genes that were potentially involved in plant growth promotion. Our study identified potential PGPR that can be used as biostimulants to produce high-quality greenhouse ornamentals with lower fertilizer inputs.

Nutrient Supplementation Configures the Bioactive Profile and Production Characteristics of Three Brassica L. Microgreens Species Grown in Peat-Based Media

Brassica L. microgreens are a fresh microscale vegetable crop of high antioxidant value and naturally dense in nutrients without the intervention of biofortification or genetic engineering. A climate chamber experiment on peat-based substrate was set up to test microgreens growth and accumulation of secondary metabolites in response to nutrient supplementation. Microgreens mineral content was analyzed through ion chromatography and total ascorbic acid through UV-Vis spectrophotometry, while carotenoids and phenolic acids were quantified by HPLC-DAD and UHPLC-HRMS, respectively. Brussels sprouts and cabbage yield was only reduced by 10%, while nitrate was reduced by 99% in the absence of nutrient supplementation. Rocket yield was prominently reduced by 47%, with a corresponding nitrate reduction of 118%. Brussels sprouts secondary metabolites were not improved by the absence of nutrient supplementation, whereas cabbage microgreens demonstrated a 30% increase in total ascorbic acid and a 12% increase in total anthocyanins. As for rocket, the absence of nutrient supplementation elicited an extensive increase in secondary metabolites, such as lutein (110%), β-carotene (30%), total ascorbic acid (58%) and total anthocyanins (20%), but caused a decrease in total phenolic acids. It is hereby demonstrated that growing microgreens on a commercial peat-based substrate without nutrient supplementation can be feasible for certain species. Moreover, it might elicit a species-dependent spike in bioactive secondary metabolites.

Use of a remediated dredged marine sediment as a substrate for food crop cultivation: Sediment characterization and assessment of fruit safety and quality using strawberry (Fragaria x ananassa Duch.) as model species of contamination transfer

A harbour sediment, previously remediated, was tested for soilless strawberry cultivation (Camarosa and Monterey cultivars), as an innovative, cost-effective and environment-friendly approach of sediment management. Sediments were tested as such (TS100) and mixed 1/1 (v/v) with a peat-based commercial substrate (TS50), using the peat-based medium as control (TS0). Substrates were characterized for some physicochemical properties (e.g. density, porosity and water capacity). Minerals (P, Ca, K, Na and Fe), heavy metals (Cu, Zn, Mn, Ni, Cr, Pb and Cd), aliphatic hydrocarbons (C > 12), polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs), dibenzodioxins and dibenzofurans were analysed in substrates and fruits. Sugars and organic acids, including the ascorbic, were also determined in fruits, as quality indicators. Notwithstanding remediation, sediments showed concentrations of Zn (206 mg kg−1), C > 12 (86 mg kg−1) and PAHs (47 mg kg−1) exceeding the limits established by the Italian L.D. 152/2006, regulating the contamination of soil in green areas, thus making its relocation in the environment not permitted as such. No evidence of fruit contamination by Cr, Pb and Cd was highlighted. Moreover, Cu, Zn and Ni fruit concentrations were comparable among treatments. Conversely, Mn showed statistically higher concentrations in TS0 fruits (56–57 mg kg−1) compared to those grown in sediment-based substrates (8–20 mg kg−1). Among organic contaminants, only dioxin-like PCBs were determined in fruits, at toxic equivalent concentrations fourfold lower than the limit established by the European Union. TS100 fruits showed a yield reduction from 40 to 70% for Camarosa and Monterey, but higher sugar and ascorbic acid contents.

Phenolic foam rooting matrices allows faster transfer and more rapid growth of Echinacea plants in greenhouse

Shoot cultures of Echinacea × Sombrero® “Salsa Red” were rooted in vitro in rigid and flexible film vented vessels, in agar-gelled medium, and in phenolic foam plugs (Oasis® InVitro Express [IVE]). Rooted plants were acclimatized to greenhouse conditions in a peat-based, soilless medium or in a larger cellular plug (Oasis® Rootcubes® Wedge®). The size of the plants leaving the laboratory, the speed of planting in greenhouse medium, and plant growth in greenhouse medium were influenced by both the laboratory and greenhouse media in which they were grown. The largest plants leaving the laboratory were from agar medium. The speed of deflasking and medium removal was greatly improved with IVE replacing agar in laboratory vessels. Planting in the Oasis® Rootcubes® Wedge® allowed a further reduction in planting time compared to planting in peat-based medium. In the greenhouse, plants in IVE/Oasis® Rootcubes® Wedge® grew more quickly and had more leaves of better quality than those from agar, planted in peat-based medium. However, the best plants (based on number of leaves, leaf length, and plug quality) in the greenhouse were from IVE, planted in peat-based medium, a treatment that still required less planting time than agar-based medium. Pre-hardening of in vitro-rooted plantlets using vessel systems that allow for ventilation and easily transferred root systems showed superior greenhouse growth simultaneous with improvements in the efficiency of workers that handled the plants. This is the direct impact of vessel systems and matrix purposefully designed to facilitate this stage of growth.

Effects of moderate and high rates of biochar and compost on grapevine growth in a greenhouse experiment

Biochar is used as soil amendment and enhancer of plant growth, but the mechanisms involved in grapevine are not understood. In this study, the short-term effects of amendments were evaluated in a trial combining three substrates (biochar, compost, peat-based media) with three doses (30, 70, 100%) along a time sequence on 1-year-old bare root cuttings of grapevine. Amendments were analyzed for elemental composition. Soil pH, electrical conductivity (EC), chlorophyll (CHL), flavonoids (FL), anthocyans (ANT) and nitrogen balance index (NBI) were measured. Biochar differed from other amendments for stable C structures, where nutrients and lignin residues were high in compost. Biochar increased soil pH, whereas biochar plus compost mixture augmented EC. The amended plants had detrimental effects on root, true and lateral leaves. Nevertheless, at the lowest rate biochar increased the primary shoot and total scion to root biomass ratio. Among biochemicals, ANT and NBI were mostly affected by biochar, while compost gave only slight increments. Thus, although biochar rate was not adequate for the shedding in open field our results suggest that biochar might be useful in nursery when used at low dosages.

Effects of Coconut Husk and Sphagnum Moss-Based Media on Growth and Yield of Romaine and Buttercrunch Lettuce (Lactuca Sativa) in a Non-Circulating Hydroponics System

A comparison was made to investigate the effects of two potting methods: coconut husk/ sphagnum moss and a plastic forestry tube with a peat-based medium (Sunshine® mix #1, Sungro Horticulture, Agawam, MA, USA), on the growth and yield of Romaine ‘Ridgeline’ and Buttercrunch ‘UH Manoa’ lettuce (Lactuca sativa) using a non-circulating hydroponics system. Two-week old lettuce seedlings were transplanted into 5 cm holes, 20 × 30 cm apart on polystyrene bead boards fitted on top of a 0.6 m wide, 1.2 m long and 25 cm deep hydroponics tanks. A standard hydroponics nutrient solution was prepared using Chem Gro® (Hydro-Gardens, Colorado Springs, CO) (8-15-36 + micronutrients), calcium nitrate [Ca(NO3)2] and magnesium sulfate (MgSO4). Each tank contained either one lettuce variety, replicated 12 times in completely randomized design. Growth and yields significantly increased in both lettuce varieties grown in coconut husk/sphagnum moss plugs which were attributed by their relatively greater water holding capacities and a more favorable media that allowed better root growth.

Spatial variation in root system activity of tomato (Solanum lycopersicum L.) in response to short and long-term waterlogging as determined by 15N uptake

Root system activity is affected by abiotic stresses, which often creates spatial differences in root conditions. This is expected to influence plants ability to cope with suboptimal conditions. Changes in root system activity were determined as 15N root uptake in top and bottom layers of potted tomato plants (Solanum lycopersicum L.), after waterlogging the bottom layer for 24 h or 5 d. The plants were grown in peat-based media; non-compacted or highly-compacted, resulting in differences in gas diffusion, air permeability and oxygen availability. The roots were affected by short-term waterlogging (24 h) by decreasing uptake in the bottom layer and increasing uptake in the pot top layer. Long-term waterlogging (5 d) decreased the 15N root uptake more in both layers. Root uptake recovered fast (within 6 h) after short-term waterlogging, whereas recovery of long-term waterlogged roots took more than 24 h, suggesting production of new root biomass. Despite affecting physical properties, medium compaction did not affect root uptake. Aboveground biomass was affected by waterlogging by increasing the dry matter percentage, decreasing nitrogen (N) percentage and increasing starch content. The results confirmed that root uptake in different layers of small pots could be distinguished by the 15N technique, which was applicable under potentially denitrifying conditions. The results demonstrated that during short-term stress in part of the root system plants increased uptake from the non-affected parts of the root system, probably as compensation for suboptimal conditions.

Method for Producing Long-cane Blackberry Plants

The objective of this study was to evaluate primocane cane training and propagation techniques for the production of long-cane blackberry (Rubus spp.) plants. Seventeen to 29 6-ft-long canes were produced from each semierect ‘Triple Crown’ and trailing ‘Siskiyou’ blackberry plant grown on the rotating cross-arm (RCA) trellis and cane training system. By early August, the lateral canes had grown beyond the top wire ≈6 ft above the ground and continued growing downward to the ground. The tips of the lateral canes reached the soil level from mid-August to mid-September at which time they were placed in 1/2-gal pots containing peat-based media. In early Oct. 2009, the tip-rooted lateral canes were cut from the stock plant at the uppermost trellis wire. Among the long-cane plants produced in 2009, 76% of buds in ‘Siskiyou’ broke, but less than 30% of buds in ‘Triple Crown’ broke in a heated greenhouse. Flowering occurred in 15% of the shoots that developed on rooted ‘Siskiyou’ long canes, but the shoots on the long-cane plants of ‘Triple Crown' were morphologically vegetative and flowering did not occur. In 2010–11, the long-cane plants were detached from the stock plants in December, January, and March. The numbers of nodes with a flowering shoot improved to 41% and 16% and the number of flowers per shoot increased to two and five flowers on long-cane plants of ‘Siskiyou’ and ‘Triple Crown’ blackberry, respectively.

Iron-[S,S′]-EDDS (FeEDDS) Chelate as an Iron Source for Horticultural Crop Production: Marigold Growth and Nutrition, Spectral Properties, and Photodegradation

Aminopolycarboxylic acid (APCA) complexones, commonly referred to as ligands or chelating agents, like ethylenediaminetetraacetic acid (EDTA) and diethylenetriaminepentaacetic acid (DTPA), are commonly used in soluble fertilizers to supply copper (Cu), iron (Fe), manganese (Mn), and/or zinc (Zn) to plants. Offsite runoff and contamination of surface waters with these chelating agents is of increasing concern as a result of their reported ability to remobilize heavy metals in sediments and their low susceptibility to biodegradation. The APCA ethylenediaminedisuccinic acid (EDDS) is a structural isomer of EDTA with the [S,S′] stereoisomer of the complexone, a compound naturally produced by actinomycetes, and is biodegradable. Information on the use of [S,S′]-EDDS as a chelating agent in formulating soluble fertilizers for the production of horticultural crops is limited. Therefore, a series of studies were conducted with the objectives of evaluating Fe[S,S′]-EDDS as an Fe-chelate fertilizer agent in the production of marigold and [S,S′]-EDDS (free ligand) and/or Fe[S,S′]-EDDS spectral properties and vulnerability to photodegrdation. Marigold grown in peat-based media were fertilized with complete nutrient solution containing 1 mg·L−1 Fe from FeEDDS, FeEDTA, or FeDTPA. There was no significant difference in foliar Fe or Mn between Fe-chelate treatments, averaging 140 μg·g−1 and 88 μg·g−1, respectively, nor were there significant differences in leaf dry weight (2.30 g) between Fe treatments. Spectra of [S,S′]-EDDS and Fe[S,S′]-EDDS produced from ferrous or ferric sources of Fe absorbed maximally in the 210 to 230 nm and 238 to 240-nm range, respectively. The [S,S′]-EDDS complexone used in the current study, a 30% assay solution, had chromaphoric properties, appearing light yellow in color. When exposed to light, Fe[S,S′]-EDDS quickly degraded at a rate at least twice that of FeEDTA.

CORRELATION BETWEEN TISSUE AND SUBSTRATE SILICON CONCENTRATION OF GREENHOUSE PRODUCED ORNAMENTAL SUNFLOWERS

The beneficial effects of the “nonessential” plant nutrient, silicon (Si), are well documented for several agricultural crops. Soilless growth media used in greenhouse production provides only limited amounts of available Si to container grown plants compared to plants grown in mineral-derived soils. Si supplementation is documented to increase resistance to biotic and abiotic stresses in greenhouse crops, which accumulate Si in their tissues. However, optimum Si fertilization rates and acceptable Si levels in tissues and substrate have not been established for floriculture greenhouse production. For this study ornamental sunflower (Helianthus annuus L. ‘Ring of Fire’) was used to investigate the relationship between substrate Si and accumulation of Si in the tissues of plants grown in a peat-based media. Weekly substrate drenches of potassium silicate (KSiO3), substrate incorporation of KSiO3 hydrous powder, or rice husk ash were used as Si supplements. Overall, leaf, stem, and flower Si concentrations of Si-supplemented plants increased compared to nonsupplemented controls. A positive correlation was observed between substrate Si concentration and leaf Si concentration for all three Si sources used in this study. Therefore, leaf tissue is the most appropriate tissue to sample in order to determine the availability of Si in a substrate and could be used to establish acceptable Si levels for soilless greenhouse floriculture.

First Report of Black Leg of Hydroponic Basil in the United States Caused by Plectosporium tabacinum.

During August 2007 and again in January 2008, compact sweet basil (Ocimum basilicum 'Genovese') plants grown hydroponically in Indiana displayed dark, irregular, stem lesions extending 2 to 3 cm above the interface of the nutrient solution. These necrotic stem lesions (black leg), observed on 20 to 30% of the basil plants caused very weak, brittle stems so that they could not be marketed fresh. Although no wilting was noted, reduced plant height was observed. Similar symptoms of blackleg and poor growth have been reported from Italy on greenhouse-grown basil infected with Microdochium tabacinum (1,2). Diseased plant samples were sent to diagnostic clinics at Purdue University and the University of Massachusetts. Stem samples were surface sterilized and plated on potato dextrose agar (PDA) acidified with 1 ml of 85% lactic acid per liter as well as onto one-quarter-strength PDA. A fungus morphologically consistent with Plectosporium tabacinum (van Beyma) M.E. Palm, W. Gams, & H.I. Nirenberg (synonyms M. tabacinum (von Arx, 1984) and Fusarium tabacinum (Gams & Gerlagh, 1968) (3) was cultured from the basil stems and identified as P. tabacinum by R. Wick. Cultures sent to J. McKemy and J. Bischof (USDA/APHIS/PPQ) and W. Elmer (Connecticut Agricultural Experiment Station) also were identified as P. tabacinum. Amplification of the 323-bp internal transcribed spacer (ITS) region (ITS1, 5.8S rRNA gene, ITS2) and subsequent BLAST alignments of the resulting sequence indicated a 98% match for Plectosphaerella cucumerina (anamorph P. tabacinum) (GenBank Accession No. U17399; MIDI Inc., Newark, DE). Inoculations were performed on basil plants grown in peat-based soilless medium in a greenhouse for 6 weeks. Immediately before inoculation, the roots were washed with tap water to remove the peat-based medium. A single basil plant was placed in each of eight, 125-ml Erlenmeyer flasks. Four flasks were filled with 100 ml of deionized water as negative controls and four were filled with a 1 × 106 CFU/ml water suspension of P. tabacinum so that the liquid reached the crown of the basil plant. Basil plants in the Erlenmeyer flasks were incubated on a laboratory bench at 23°C. After 24 h, the solutions in all flasks were discarded and each flask and root system was rinsed three times with deionized water. The plants were then incubated in deionized water on the laboratory bench for four to five additional days. Within 4 days, dark brown-to-black stem lesions similar to those observed originally on basil plants in the hydroponic production greenhouse developed on the plants at the water interface and extended up the stem. Lesions extended a mean of 22 mm above the water level on inoculated plants. Control plants remained symptomless. P. tabacinum was recovered from symptomatic tissue of inoculated plants to complete Koch's postulates. The experiment was repeated several times with similar results. Further evidence of pathogenicity was obtained by stem inoculation of basil plants growing in a soilless medium. These data indicate that P. tabacinum was the causal agent of the symptoms observed on the hydroponic basil. To our knowledge, this is the first report of P. tabacinum causing 'black leg' and reduced growth on basil in the United States and the first report in the world of P. tabacinum on hydroponic basil.

STRAWBERRY GENOTYPES DIFFER IN THEIR RATIO OF SHOOTS TO ROOTS, BASED ON DRY WEIGHT

Previous observations of strawberry roots of plants grown in peat-based medium in a screenhouse or grown in the field in soil indicated that genotypes differ in root length and volume. This experiment was designed to evaluate a large number of genotypes to better quantify this variability and to identify those genotypes with large root systems. Plant material consisted of 100 cold-stored dormant genotypes and 71 micropropagated genotypes. Plants were grown for 8 weeks in a greenhouse, then dry weights of shoots, roots and stolons were obtained. For the cold-stored plants, root dry weight ranged from 0.74 g for 'K99-5' to 2.18 g for 'Brunswick'. The shoot-to-root ratio ranged from 2.51 for 'K03-2' to 5.43 for 'K99-36', with a mean of 3.51. For the micropropagated plants, root dry weight ranged from 0.26 g for 'BC4-41-67' to 2.14 g for 'WSU2464', with a mean of 1.01 g for 71 genotypes. The shoot to root ratio ranged from 2.01 for 'BC92-20-85' to 6.72 for 'BC4-9-5', with a mean of 4.44 for 70 genotypes. Genotypes identified in this study as having large root systems or small shoot:root ratios can be used to test whether these types are more tolerant of root pathogens or abiotic stresses.

Effects of Light Intensity and Paclobutrazol on Growth and Interior Performance of Pachira aquatica Aubl.

Pachira aquatica Aubl. has recently been introduced as an ornamental foliage plant and is widely used for interiorscaping. Its growth and use under low light conditions, however, have two problems: leaf abscission and accelerated internode elongation. This study was undertaken to determine if production light intensity and foliar application of paclobutrazol [β-(4-chlorophenyl)methyl-α-(1,1-dimethylethyl)-1H- 1,2,4- triazole-1-ethanol] improved plant growth and subsequent interior performance. Two-year-old P. aquatica trunks were planted in 15-cm diameter plastic pots using a peat-based medium and were grown in a shaded greenhouse under three daily maximum photosynthetic photon flux densities (PPFD) of 285, 350, and 550 μmol·m−2·s−1. Plant canopy heights, average widths, and internode lengths were recorded monthly over a 1-year production period. Two months after planting, the plant canopy was sprayed once with paclobutrazol solutions at concentrations of 0, 50, and 150 mg·L−1, ≈15 mL per plant. Before the plants were placed indoors under a PPFD of 18 μmol·m−2·s−1 for 6 months, net photosynthetic rates, quantum yield, and light saturation and compensation points were determined. Results showed that lowering production light levels did not significantly affect canopy height, width, or internode length but affected the photosynthetic light response curve and reduced the light compensation point. Foliar application of paclobutrazol reduced internode length, thereby resulting in plants with reduced canopy height and width and more compact growth form. Paclobutrazol application also reduced the light compensation point of plants grown under 550 μmol·m−2·s−1. Plants with the compact growth form did not grow substantially, dropped fewer leaflets, and thus maintained their aesthetic appearance after placement indoors for 6 months. These results indicated that the ornamental value and interior performance of P. aquatica plants can be significantly improved by producing them under a PPFD range between 285 and 350 μmol·m−2·s−1 and foliar spraying of paclobutrazol once at a concentration between 50 and 150 mg·L−1.

PROPAGATION AND PRODUCTION OF ZAMIOCULCAS ZAMIIFOLIA

PROPAGATION AND PRODUCTION OF ZAMIOCULCAS ZAMIIFOLIA

MICROBIOLOGICALLY IMPROVED PEAT-BASED MEDIA FOR NURSERY PRODUCTION BY ADDITION OF ARBUSCULAR MYCORRHIZAL FUNGI

MICROBIOLOGICALLY IMPROVED PEAT-BASED MEDIA FOR NURSERY PRODUCTION BY ADDITION OF ARBUSCULAR MYCORRHIZAL FUNGI