Soilless Mix Research Articles

Indoor Vegetable Production: An Alternative Approach to Increasing Cultivation.

As the world's population is increasing exponentially, human diets have changed to less healthy foods resulting in detrimental health complications. Increasing vegetable intake by both rural and urban dwellers can help address this issue. However, these communities often face the challenge of limited vegetable supply and accessibility. More so, open field vegetable production cannot supply all the vegetable needs because biotic and abiotic stress factors often hinder production. Alternative approaches such as vegetable production in greenhouses, indoor farms, high tunnels, and screenhouses can help fill the gap in the supply chain. These alternative production methods provide opportunities to use less resources such as land space, pesticide, and water. They also make possible the control of production factors such as temperature, relative humidity, and carbon dioxide, as well as extension of the growing season. Some of these production systems also make the supply and distribution of nutrients to crops easier and more uniform to enhance crop growth and yield. This paper reviews these alternative vegetable production approaches which include hydroponics, aeroponics, aquaponics and soilless mixes to reveal the need for exploring them further to increase crop production. The paper also discusses facilities used, plant growth factors, current challenges including energy costs and prospects.

Suppression of Hemp Powdery Mildew Using Root-Applied Silicon

Powdery mildew (Golovinomyces spadiceus) is the most common disease of greenhouse cannabis. Most hemp grown for cannabinoid production is propagated by cuttings or started from feminized seed in greenhouses and then moved outdoors, while most marijuana and some hemp are grown entirely indoors. To determine the effects of silicon on powdery mildew in the greenhouse, silicon was applied to hemp roots in a peat-based soilless mix and evaluated for plant uptake and disease suppression over a 6-week period. This study confirmed that there was a negative linear relationship between percent silicon accumulation in leaf tissue and the percent powdery mildew per leaf area. Mildew severity in the upper canopy was significantly reduced at 300 kg/ha of silicon, while 600 kg/ha was needed for the mid canopy. Results confirmed that silicon may be a useful tool for the integrated management of powdery mildew. As the cannabis market expands, silicon can serve as a viable option for greenhouse growers, especially for plants grown in soils or soilless mixes low or limiting in soluble silicon.

Dimethenamid Persistence and Leaching Potential in a Soilless Mix1

Abstract Dimethenamid and the granular combination product pendimethalin plus dimethenamid are herbicides registered for use in nursery production and landscape maintenance. The objectives of this study were: (1) to compare the effectiveness of sprayed dimethenamid and the granular combination of pendimethalin plus dimethenamid in container nursery production, (2) to determine the impact of formulation on leaching of dimethenamid in soilless media versus field soil and (3) to determine the influence of irrigation volume on herbicide leaching. Dimethenamid is less mobile in pine bark than field soil, while pendimethalin is more mobile in pine bark. The leaching profile for the granular pendimethalin plus dimethenamid combination product was similar to dimethenamid in field soil and similar to pendimethalin in pine bark. There was no significant difference in herbicide movement in pine bark or field soil after doubling the irrigation volume from 17.8 cm (7 in) to 35.6 cm (14 in). Compared to pendimethalin, dimethenamid leaches less in pine bark, explaining its greater effectiveness for weed control in container production. Index words: Herbicide leaching, soilless mix, pine bark, ornamentals, adsorption. Species used in this study: southern crabgrass [Digitaria ciliaris (Retz.) Koel.]; spotted spurge [Chamaesyce maculata (L.) Small]. Chemicals used in this study: dimethenamid (Tower); dimethenamid plus pendimethalin (FreeHand); pendimethalin (Pendulum 2G).

Nitrogen Dynamics of Strawberry Cultivation in Vermicompost-Amended Systems

ABSTRACTThe use of vermicompost as a soil amendment is suggested as a method to reduce nitrogen (N) losses in crop production; however, it is unclear whether and how vermicompost can affect water quality after a significant irrigation or rainfall event. Bare-root strawberry plugs were grown in 1-gallon plastic pots. The treatments consisted of two media: (1) a peat:perlite soil-less mix and (2) a fine sand soil. Each media was amended with three levels of dairy manure vermicompost: 0, 10, and 25% by weight, and a biweekly synthetic fertilizer treatment of 150 mg N-P-K L−1 evaluated in a full factorial randomized block design. Drainage water from each plant was collected each week for 18 weeks and analyzed for NO3− concentration. In the first 2 weeks, high (1000–5000 mg L−1) amounts of NO3− leaching occurred in all vermicompost-amended media relative to non vermicompost-amended media, but this leaching significantly (p < 0.01) decreased over time across all vermicompost treatments. Strawberry growth response to 10% vermicompost was similar to synthetic fertilizer only treatments. Plants grown with vermicompost at 25% with synthetic fertilizer had the highest above-ground vegetative biomass (15.3 g) relative to plants with synthetic fertilizer only (5.3 g). These data suggest vermicompost addition rates of 10 and 25% by weight promote high vegetative biomass in greenhouse strawberry but may facilitate high initial nitrate leaching, which can negatively affect water quality and environmental health.

Biochar Rate and Transplant Tray Cell Number Have Implications on Pepper Growth during Transplant Production

Biochar, a carbon-rich material derived from the pyrolysis of organic matter, exhibits beneficial chemical and physical properties when added to a soilless medium. Research on the use of biochar to improve plant productivity and growth has increased over the past decade, and has focused on using biochar as an alternative to sphagnum peatmoss. However, little work has been done to determine whether biochar can be used to partially replace commercially available sphagnum peatmoss–based greenhouse medium in vegetable transplant production. This study investigated the potential for supplementing a greenhouse growing medium with biochar for ‘Paladin’ pepper (Capsicum annuum) transplant production. Biochar was added to a soilless mix at rates of 0%, 20%, 40%, 60%, or 80% (by weight). Pepper seedlings were grown for 56 days in 50-, 72-, or 98-cell transplant trays at each of the five levels of biochar concentration. Germination increased in the 50- and 72- cell trays with 20%, 40%, and 60% biochar; however, biochar had no effect on germination in the 98-cell tray. Seedling height and dry weight decreased as biochar concentration and cell number increased. Seedling stem diameter also decreased with increasing cell number and biochar concentration. Leaf SPAD readings (indirect measurement of chlorophyll) decreased with increasing biochar rate. Medium pH increased with increasing biochar application rates. Higher rates of biochar (60% and 80%) increased pH well beyond 7.0 and negatively affected transplant growth. Overall results indicate positive effect of biochar in sphagnum peatmoss–based growing mix on seedling growth characteristics; although higher biochar concentrations could negatively affect seedling growth. Biochar can successfully replace up to 40% of sphagnum peatmoss–based growing medium and serve as a sustainable alternative medium in vegetable transplant production.

Method to evaluate the efficiency of manual overhead irrigation in citrus rootstock liner production

Brazil produces grafted citrus seedlings in closed screen houses to reduce pest and disease incidence. Irrigation is usually performed by hand using either breaker nozzles or drilled polyvinyl chloride (PVC) pipe wands on garden hoses. Rootstocks are produced in cone-shaped containers filled with soilless potting mix. Since the containers have a small upper diameter, nutrient solution capture is reduced with the potential to cause environmental contamination from inefficient fertigation. This study provides a method to assess the efficiency of manual overhead irrigation systems used in liner production. The method consists of determining both the volume of water applied and volume lost (i.e., directly and by percolation) in order to obtain an estimate of the percentage of water loss, irrigation efficiency, and the drainage fraction. The method was tested in a commercial facility under standard production practices. The method’s attributes included simplicity, quick sampling and data collection, and accuracy. The evaluated nursery was found to have low irrigation efficiency (27.14%) and excessive nutrient solution losses (72.86%). Considering an average production of 300,000 liners per year on 20,000 m2, we determined an annual solution loss of 221.8 m3 with an average environmental release of 158.9 kg of fertilizer. Therefore, more efficient irrigation systems are necessary for sustainable citrus rootstock liners production.

Development of an in vitro propagation method for the classified New York State-threatened native species Agrimonia rostellata

We developed an in vitro micropropagation protocol for Agrimonia rostellata Wallr. (Rosaceae), a New York State–threatened native plant species. For initial experiments, we investigated methods for disinfection of nodal sections from field-grown plants before transfer to culture medium to generate contaminant-free plant material. Fungal contamination was most prevalent. The only effective treatment was a combination of washes in a detergent solution followed by treatment with 70% ethanol, 10% bleach, plus vacuum infiltration with a solution of the antifungal compound Miconazole. We also found it was necessary to include 20 mg/l Miconazole in the culture medium to prevent fungal contamination. A Murashige and Skoog–based medium supplemented with 0.1 mg/l indole-3-butyric acid (IBA), 5 g/l charcoal, and 7 g/l agar was the only medium tested that resulted in both the development of multiple shoots and rooting. A starting population of 35 contaminant-free, in vitro plants was scaled up to 1013 plants in 6 mo. All rooted plantlets were successfully established in a soilless mix and then transferred to the field. These methods proved to be effective for generating a large population of A . rostellata for replicated field studies to identify the cause(s) of its decline.

Water use efficiency, nutrient leaching, and growth in potted marigolds affected by coconut coir dust amended in substrate media

Coconut coir dust amended in substrate had effects on water use and some growth in potted marigolds (Tagetes erecta ‘Antigua Yellow’). This study was performed to clarify the effect of coir dust amended in substrate media on water use efficiency and nutrient leaching in potted marigold. ‘Antigua Yellow’ seeds were sown in peat moss to develop 2 pairs of true leaf, then seedlings were randomly transplanted into 15 cm plastic pots containing soilless mix media (40% rice husk charcoal, 20% rice husk, 20% sand and 20% compost leaves; by volume) and followed by coconut coir dust amended treatments with 0, 25, 50 and 75% (v/v). The results exhibited that all amended coconut treatments could improve the physical properties of mix media by decreasing the estimated bulk density, but increased the total porosity (%) and water filled pore (%). Fifty percent coir dust treatment seems to reduce accumulated ET, crops evapotranspiration (ETc) and transpiration per leaf area unit per day. Hence, 50% coir dust portion gave the highest water use efficiency (WUE) and the lowest crop co-efficient (Kc) parameter. Nevertheless, 75% coir dust portion also reduced some nutrient leachate in the runoff solution; nitrate (NO3−) leachate at early growth stage and phosphate leachate (PO43−) at flowering and senescence. Positive correlation was observed between total leachate volume and total phosphate concentration leachate (R = 0.98). Almost all plant growth parameters had diverse responses during the comparison of each different coconut coir dust portion, but flowering yield (total FW and total number) were prone to be promoted by 75% coir dust treatment.

Longevity of Uromyces transversalis, Causal Agent of Gladiolus Rust, under Various Environmental Conditions

To help determine if gladiolus rust may spread to new areas of the United States, we studied effects of different temperature and moisture conditions on longevity of Uromyces transversalis urediniospores. Treatments consisted of gladiolus leaf pieces, with actively sporulating uredinia, placed in mesh bags in a plastic beaker without soil (dry) or plastic bags covered in damp soil (damp). These treatments were either held in a greenhouse at 22–26°C (warm) or refrigerator at 4°C (cool). After 14 days, 59% of urediniospores maintained under warm, dry conditions were viable compared to only 1% under warm damp conditions. After 56 days, viability dropped to 3% and near 0%, respectively. Under cool conditions, by 91 days germination dropped to 0.7% and 0%, respectively. To determine the potential for corms or soilless mix from infected plants to harbor inoculum, infected gladiolus plants were maintained in a growth chamber progressively simulating fall and winter. Following foliage senescence, corms from infected plants were removed from the soilless mix, stored 11 months at 4°C, and planted in noninfested soilless mix in the greenhouse. The pots containing soilless mix in growth chambers, upon removal of corms present on infected plants, were maintained in the chambers until fall and then replanted with healthy corms. No pustules developed on either set of plants, indicating that corms from infected plants had not been infected, urediniospores had not survived in the soilless mix, and urediniospores on or in soil did not perpetuate the disease. Accepted by publication 15 January 2015. Published 6 April 2015.

First Report of Clubroot on Canola Caused by Plasmodiophora brassicae in North Dakota.

North Dakota leads the United States in canola (Brassica napus L.) production (4). A canola field with a distinct patch of dead plants spreading over an area of approximately 0.4 ha was detected in Cavalier County, North Dakota, in early September 2013. Numerous spots within the patch had plant mortalities >80%. Dead plants pulled from the soil had roots with severe galling and clubbing. Clubbed roots were brittle and disintegrated easily when pressed between fingers. Root and soil samples collected at several locations within and outside the affected patch were pooled in separate groups. All plants collected in the patch were symptomatic but those collected outside were not. In the lab, total genomic DNA from three symptomatic and two healthy root samples was extracted using standard procedures and freehand slices were prepared for observation with a compound microscope. Also, DNA from pooled soil samples was extracted using FastDNA Spin Kit for Soil (MP Biomedicals, Solon, OH). Round resting structures ranging from 2.2 to 4.2 μm in diameter were observed by microscopic examination of symptomatic root tissues. These structures resembled those typically produced by Plasmodiophora brassicae Woronin. This initial identification was later confirmed through PCR analysis using the species specific primers TC1F/R and TC2F/R (1). PCR products of 548 bp (TC1F/R) and 519 bp (TC2F/R) were produced in the three symptomatic and two infested soil samples, confirming the presence of P. brassicae. PCR amplicons were not detected in healthy root and soil samples. Pathogenicity tests were conducted in greenhouse to fulfill Koch's postulates. Briefly, five square plastic pots (10 × 10 × 13 cm) were filled with a 10-cm layer of Sunshine Mix #1 potting mix (Fison Horticulture, Vancouver, BC, Canada) and then 1 g of ground root galls (approximately 5 × 105 resting spores) was spread evenly on its surface and covered with 2 cm of soilless mix. A similar number of pots were filled only with soilless mix and used as controls. All pots were planted with two seeds of canola cv. Westar and incubated in greenhouse conditions at 21°C and 16 h light daily. The experiment was conducted twice. Four weeks after planting, all plants in the inoculated pots had developed galls while plants in control pots were symptomless. Presence of P. brassicae resting spores in the newly developed galls was confirmed by microscopic observations and PCR. Based on the symptoms, morphology of resting spores, PCR reactions, and pathogenicity tests, we confirm the presence of P. brassicae on canola. While P. brassicae has been reported as widespread in North America (2), to our knowledge, this is the first report of clubroot on canola in North Dakota and the United States. Clubroot became the most important disease affecting canola production in central Alberta, Canada, within 5 years of its discovery in 2003 (3); since then, the disease has been detected in Saskatchewan and Manitoba (3), Canadian provinces that share borders with North Dakota. Considering the difficulties in management of clubroot, measures should be initiated to limit the spread of the disease before it could pose a threat to United States canola production.

Investigation of Seed Treatments and Fertilizer on Growth ofPenstemon tubaeflorus

Penstemon tubaeflorus is a North American prairie forb of conservation concern. Protocols for seed germination and transplant production involving fertilization are needed for conservation purposes. Our objectives were to compare techniques for breaking seed dormancy and increasing germination, and to investigate fertilizer on growth of Penstemon tubaeflorus. Seed treatments were hickory smoke seasoning solution (1:10, 1:100, 1:500, and 1:1,000), light vs. dark, prairie plant ash solution (2, 4, 8, and 16 g/L), and cold moist stratification (1 or 2 mo at 4°C). Seeds were germinated in Petri dishes in germination chambers and counted for 21 d. For hickory solutions, 1:100 had the highest germination (51%), and seeds germinated in light, but not in the dark. For ash solutions, 8 g/L (6%) and control (4%) germinations were higher than 2 g/L with 4 g/L and 16 g/L being intermediate. Germination increased for both stratification durations (37%) compared to control (2%). For fertilizer studies, seeds were planted in soilless mix with no fertilizer, liquid fertilizer (20–20–20 at 1.25 g/L water), or solid fertilizer (14–14–14 slow release at 14.6 g/L mix) in growth chambers. After 7 wk, shoot fresh mass, leaf number, leaf area, crown diameter, root length, and shoot dry mass were measured. Seedling growth was greatest with solid fertilizer compared to control and liquid fertilizer, which were similar. Overall, hickory solution at 1:100 with light produced the highest percent germination among all treatments, and solid fertilizer was most effective for transplant development. These findings are useful for management or restoration of P. tubaeflorus populations.

Effect of inoculum density and quantitative PCR-based detection of Rhizoctonia solani AG-2-1 and Fusarium avenaceum on canola

Canola seedling blight, caused by Rhizoctonia solani, and Fusarium spp., can result in large yield losses to canola (Brassica napus) at high inoculum pressure. The effect of inoculum density was studied by mixing different amounts of R. solani AG-2-1 and Fusarium avenaceum into a sterilized natural soil and soil-less mix (2:1, v:v) separately, and recording seedling emergence, damping-off and seedling height within ten days after seeding; root rot severity at 12 days after seeding and seed yield at harvest on canola cultivars ‘45H29’ and ‘73-77RR’. Root rot severity increased and emergence, plant height and seed yield decreased with increased inoculum density of both R. solani and F. avenaceum. For quantification of R. solani AG-2-1, a primer and TaqMan probe set (Rs21F/Rs21R/Rs21P) was designed based on the nuclear ribosomal internal transcribed spacer (ITS) region of R. solani AG-2-1. From a conventional PCR amplification, an 88-bp product was amplified from all isolates classified as AG-2-1 with the primers Rs21F and Rs21R. No product was amplified with DNA from isolates belonging to other anastomosis groups of R. solani, other pathogens or the host plant. By using quantitative PCR, DNA amounts as low as 100 fg of R. solani AG-2-1 were detected. The quantity of DNA from soil samples with different inoculum densities estimated using qPCR was highly correlated to the number of colony-forming units (cfu) obtained from the same soil samples for both R. solani AG-2-1 and F. avenaceum.

First Report of Fusarium cuneirostrum Causing Root Rot Disease in Dry Bean (Phaseolus vulgaris) in Canada.

Root rot is a major disease of dry bean and can cause significant yield reductions due to weakened root systems and poor plant stands. An in-depth study on root rot pathogen identification was conducted in 2011 in three commercial dry bean fields from the major production areas in Manitoba. Ten plants, sampled at each of four random sites within each field, were rated for disease severity. Twenty roots were processed for pathogen isolation and identification in the laboratory. Roots were cut into eight sections (~1 cm) and surface-sterilized in a laminar flow bench. Four root sections were placed on potato dextrose agar plates amended with 0.02% streptomycin sulfate (PDA-Strep) and four root sections were placed on peptone-pentachloronitrobenzene agar amended with 0.1% streptomycin sulfate and 0.012% neomycin sulfate. Afterward, 960 monosporic cultures were obtained representing 320 single spore isolates of potential root rot pathogens per commercial field. Common monosporic cultures from each field were subcultured on PDA-Strep and Spezieller Nährstoffarmer Agar (SNA) media. Based on morphological characteristics, 74 isolates were identified as Fusarium cuneirostrum (1). Colonies grew slowly on PDA-Strep with undulated margins, radial cream-grey mycelia, and conidia pustules with a cream-greyish pigmentation. Sporodochial conidia were falcate, mostly 5-septate, with a wedge shape and slightly protruding basal foot cell (56.3 to 71.8 × 4.6 to 6.2 μm on average). Species identity was confirmed for two isolates by sequencing the translation elongation factor 1 alpha (EF1-α) gene (2), the internal transcribed spacer (ITS) region (4), and the ribosomal intergenic spacer (IGS) (3) (GenBank Accession Nos. KF530848, KF530849, and KF025648 to 51). Sequence homology was compared using BLAST analysis and the FUSARIUM-ID database. The F. cuneirostrum isolates were deposited at the Canadian Collection of Fungal Cultures (DAOM 242540 and 242541). Pathogenicity screenings of two isolates was performed using sterilized seed of navy bean cv. Envoy. Seeds were germinated on moist filter paper for 3 days at 25°C and then inoculated by immersion in a prepared conidial suspension (2.5 × 105 conidia/ml) for 5 min. Seeds of the controls were immersed in sterile water. After inoculation, the germinated seeds were planted in 10-cm diameter pots, filled with sterile soilless mix (Sunshine #3). In the greenhouse, the experiment was arranged as a completely randomized design with three replicates with four germinated seeds per isolate, and was repeated twice. Disease assessment was performed 14 days after inoculation. Infected plants displayed dark brown lesions on the hypocotyl and primary root with a disease severity of 4 scored on a 0 to 5 scale. Fusarium cuneirostrum was re-isolated from roots of symptomatic plants. To our knowledge, this is the first report of F. cuneirostrum causing root rot of dry bean in Canada. It has been previously isolated from mung bean (Vigna radiata) in Ontario (1).

Seed ecology ofSynthyris bullii(Plantaginaceae), a rare endemic of the midwestern USA

Many rare plant species are declining owing to habitat destruction and degradation. Because many populations of rare species suffer low recruitment, a good understanding of seed ecology is crucial for developing effective conservation and management plans. In this study, we examine the effects of shading, seed longevity, and soilless mixes on seed germination for the rare midwestern USA endemic Synthyris bullii (Eaton) A. Heller. Seed germination studies were conducted in a greenhouse environment utilizing seeds from populations collected in Illinois in 2008, 2009, and 2010. In the shading study, both control (66.7% ± 1.3%) and green wrap (63.7% ± 1.3%) had similar and greater percent seed germination than the solid white wove paper (59.5% ± 1.3%). Percent seed germination was similar for seeds collected in 2010 and 2009 (59.5% ± 3.3% and 55.1% ± 4.4%, respectively) in the longevity study, but germination was lower for seeds collected in 2008 (27.1% ± 4.0%) compared with both of the other years. For the soilless mixes study, seeds sown in only one of the three media, Fafard Super-Fine Germinating Mix, emerged (3.5% ± 1.0%). Results from these studies suggest that for S. bullii, (i) seeds may be shade tolerant, (ii) seed viability lessens with age, and (iii) seedlings require a special soilless mix to grow. The information generated by this study can provide guidelines for better seed storage and germination protocols for the conservation of this rare plant species.

Undergraduate Sustainable Learning: Effects of Sustainable Soilless Media on Production and Sensory Evaluation of Cucumbers, Basil, Parsley, and Lettuce

Modern greenhouse production has been ~100% reliant on fossil fuels for all inputs (glazing, heating, fertilization, lighting, post-harvest). Recent innovations may reduce fossil fuel dependence but their effectiveness may not be thoroughly tested. To promote education in sustainable production, undergraduate students in Greenhouse Management class (Hort 3002W; University of Minnesota) tested the effectiveness of two organic or ‘sustainable’ soilless media (Sunshine Natural and Organic Growing Mix, Sungro Metro-Mix Special Blend) with a control (Sunshine LC8 Professional) for crop production (height, leaf/flower number, yield) and sensory evaluations (appearance, texture, taste, purchase) of cucumbers (‘Big Burpless Hybrid’, ‘Sweet Burpless Hybrid’), basil (‘Opal Purple’, ‘Redleaf’), parsley (‘Green River’, ‘Extra Curled Dwarf’, ‘Hamburg’), and lettuce (Flying Saucer ‘Green’, ‘Red’). Significant differences between sustainable vs. control soils occurred for plant growth, depending on vegetative or reproductive traits, crops, and cultivars. These differences occasionally disappeared for sensory evaluation of edible components. In most crops, however, cultivars were highly significant factors. Undergraduate research can be used to provide directionality for future vegetable and herb plant breeding to focus on creating cultivars with increased yield and high consumer acceptance when grown in sustainable greenhouse soilless mixes.

Seedling age and inoculum density affect clubroot severity and seed yield in canola

Hwang, S. F., Ahmed, H. U., Strelkov, S. E., Gossen, B. D., Turnbull, G. D., Peng, G. and Howard, R. J. 2011. Seedling age and inoculum density affect clubroot severity and seed yield in canola. Can. J. Plant Sci. 91: 183–190. Clubroot, caused by Plasmodiophora brassicae, is a serious threat to canola (Brassica napus, B. rapa) production in western Canada because of its long-lived resting spores, high spore production potential, and negative impact on seed yield when inoculum pressure is high. The effect of inoculum density was studied by diluting heavily infested field soil with pathogen-free soil-less potting mix at seven increments, ranging from completely pathogen-free to 100% infested soil, and also by incorporating resting spores into the soil-less mix at concentrations of 1×105to 1×108spores cm−3, along with a non-inoculated control. Seed of the susceptible canola cultivar 34 SS 65 was planted in soil of each treatment, grown to maturity, and rated for plant height, seed yield, and clubroot severity (0–3 scale) at harvest. Clubroot severity increased and plant height and seed yield decreased with increasing inoculum density. To assess the effect of seedling age on reaction to clubroot, resting spores of P. brassicae were inoculated onto roots of 1-, 2-, 3- and 4-wk-old seedlings of 34 SS 65. In addition, seed (i.e., 0-wk-old seedlings) was sown into infested soil. Inoculation of young seedlings resulted in higher clubroot severity, shorter plants and lower yield than inoculation of older seedlings. These results indicate that seed treatment fungicides with a long residual period (4 wk or more) may be useful for the management of clubroot.

EFFECT OF NPK LEVELS ON GROWTH AND BULB QUALITY OF SOME GEOPHYTES IN SUBSTRATE CULTURE

EFFECT OF NPK LEVELS ON GROWTH AND BULB QUALITY OF SOME GEOPHYTES IN SUBSTRATE CULTURE

Response of Six Begonia Species to Fertilizer Concentration and Substrate pH

Begonia albopicta, B. cucullata var. cucullata, B. echinosepala var. elongatifolia, B. holtonis, B. foliosa var. miniata and B. 'Fuchsifoliosa' are conserved at the Ornamental Plant Germplasm Center (OPGC), in Columbus Ohio as a source of germplasm for breeders and researchers. No cultural information for these species is available. Our objective was to evaluate the response of the above mentioned species to different fertilizer concentrations and substrate pH levels. Rooted cuttings were transplanted into plastic containers using a soilless mix. One of five concentrations ranging from 20 to 600 mg·L -1 N of 17-5-17 water soluble fertilizer were applied in irrigation water for 12 weeks. We found significant responses to the fertilizer concentrations and differences among species on weekly measured substrate EC, shoot length, leaf area, dry weight, average number of inflorescences, and SPAD readings. Growth parameters and visual observations were used to determine optimal fertilizer concentration. High quality B. albopicta, B. cucullata var. cucullata, B. echinosepala var. elongatifolia, and B. holtonis plants were obtained with 200 to 300 mg·L -1 N. On the other hand, low fertilizer concentration was found to be better for B. foliosa var. miniata and B. 'Fuchsifoliosa' in order to avoid high salt stress causing plant death. Seven different pH ranges of the peat-based substrates were obtained by adding different rate of dolomitic hydrated lime ranging from 1.0 to 2.6 kg·m 3 . pH was monitored weekly and maintained accordingly by adding flowable lime or a diluted sulfuric acid solution. The inflorescence number and SPAD readings were significantly different among six species, but there was no significant effect of substrate pH. Significant interaction between species and substrate pH was found in shoot length, leaf area, and dry weight. Substrate pH between 5.6 and 6.0 was found to be adequate for B. albopicta, B. echinosepala var. elongatifolia and B. holtonis. B. foliosa var. miniata plant mortality was observed when grown at a substrate pH below 5.2. The information presented in this work will be useful to OPGC personnel in the maintenance of these species at their facilities, as well as to begonia breeders and collectors.

First Report of Bipolaris oryzae Causing Leaf Spot of Switchgrass in Mississippi.

'Alamo' switchgrass (Panicum virgatum L.) seedlings growing in a soilless mix exhibiting dark brown, irregular-shaped foliar lesions with black borders were submitted to the Mississippi State University Plant Disease Diagnostic Laboratory in the summer of 2009 from a local forest products company. Symptomatic tissues were plated onto water agar (WA) and incubated for 21 days on a laboratory bench top with a 12-h photoperiod at 22°C. An asexual, sporulating, dematiaceous hyphomycete identified as Bipolaris oryzae (Breda de Haan) Shoemaker was observed. Conidiophores were single, mostly straight, multiseptate, brown, and ranging from 138 to 306 × 7.7 to 15.3 μm and averaged 221.6 × 10.7 μm. Conidia were golden brown, multiseptate, ranging from 3 to 10 septa, straight to slightly curved to fusoid, wider midway, and tapering toward the terminal cells. Conidia measured 40.8 to 109.7 × 10.2 to 20.4 μm and averaged 75.8 × 13.8 μm. Morphological characteristics of B. oryzae were similar to those described by Drechsler (1) and Sivanesan (3). The internal transcribed spacer (ITS) region of ribosomal DNA from four pure culture colonies derived from single conidia was amplified by PCR using ITS1 and ITS4 primers. The resultant 572 bp was sequenced for isolates 86 through 89 (GenBank Accession Nos. GU222690-93). The sequences were 99% similar to the sequence of B. oryzae strain ATCC-MYA 3330 (GenBank No. FJ746665) isolated from P. virgatum. Pathogenicity of isolates 86 and 88 was confirmed by inoculating sterile potting mix with a fungal slurry. Sterile Alamo switchgrass seeds were sown into the infested soil in Magenta boxes and incubated for 6 weeks in a growth chamber with a 14-h photoperiod at 30°C. Leaf lesions and leaf blight were observed in seedling stands growing in B. oryzae-infested soil. Lesions were excised and plated onto WA. Sporulation of B. oryzae was observed on symptomatic tissue. In the interim, 300 nonsterilized Alamo switchgrass seeds of the same seed lot as the original symptomatic seedlings and originating from Oklahoma were plated onto WA (10 seed per plate). The seeds were incubated on the bench top as previously described. The experiment was repeated and B. oryzae colonized 1.4% of the total switchgrass seeds evaluated, indicating seed transmission and subsequent seedling infection as previously observed in the original seedlings. Leaf spot, caused by B. oryzae, was first reported as a new disease of switchgrass in North Dakota (2). In the summer of 2009, the authors observed leaf spot in four cultivars of switchgrass, including Alamo, growing in research plots in Webster County, MS. Twenty-two isolates of B. oryzae were recovered from diseased leaves of these switchgrass cultivars. To our knowledge, this is the first report of B. oryzae causing leaf spot of switchgrass in Mississippi, which broadens the natural distribution of this disease.

EVALUATING PERFORMANCE AND STABILITY OF POLYETHYLENE TEREPHTHALATE (PET) AND CELLULOSE POLYMER AS SOILLESS MIX COMPONENTS

In the U.S., concerns over the long-term sustainability of peat, perlite, and other media components have led to searches for alternative materials. FiberFill, a synthetic fiber made of recyclable polyethylene terephthalate, and Tencel, a cellulose fiber, are new materials with potential as substrate components. FiberFill blocks have already been used for hydroponic vegetable production, but its suitability as well as the suitability of Tencel has not yet been tested as soilless mix components. The growth of several floriculture crops was tested using substrates containing different proportions of the two polymers. Furthermore, the long-term stability of the materials was tested by measuring respiration rates of the different components by themselves or as blends with peat. A peat- or coir-based mix was amended with the polymers up to 100% of the final volume and fertigated with water-soluble fertilizer as needed. Visual observations of plants, dry weight (DW), leaf area (LA), and consumer preference were measured. Plants grown in 100% FiberFill or Tencel were shorter and had smaller DW and LA than plants grown in partially-amended substrates with the exception of begonia, which were largest in 100% and 75% FiberFill. Substrates containing 50% FiberFill produced plants that were equal to or larger than substrates containing less polymer. Plants grown in Tencel-containing mixes were consistently smaller than plants grown in substrates containing an equal amount of FiberFill. Initial respiration rates of Tencel were lower than those of peat or peat:perlite blends, but after only ten days, respiration rates of Tencel increased after saprophytic organisms colonized the material. These results indicate that FiberFill has potential as soilless mix component, but the high respiration rates suggest Tencel would not be suitable for long-term (>6 months) production. However, the movement of the U.S. floriculture industry towards sustainability likely favors the adaptation of the cellulose-based component, Tencel.