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Matthew D. Taylor, Paul V. Nelson and Jonathan M. Frantz

The cause of sudden substrate pH decline by geranium is unknown. Low Fe and low P have been shown to cause many plant species to acidify the substrate. Research was done to determine if low Fe or P stresses caused four geranium (Pelargonium ×hortorum Bailey) cultivars to acidify nutrient solution. Two cultivars were susceptible and two resistant to substrate acidification based on a grower survey. Rooted geranium cuttings were transferred to 4-L containers containing modified Hoagland's solution with N supplied as 15% NH4 and 85% NO3. The plants were grown in a greenhouse for 44 days. Treatments consisted of a complete nutrient solution and two similar solutions devoid of either Fe or P. Solutions pH was set at 5.8, changed weekly, and tested 3 and 6 days after each change. Because all cultivars showed similar responses, results were combined. Twenty days after transplanting (DAT), plants in all treatments, including control, caused solution pH to fall below 5. At 37 DAT, the solution pH levels for control, minus Fe, and minus P treatments were 4.1, 3.7, and 3.6, respectively. Results indicated that geranium is an acidifying plant when N is supplied as 15% NH4 and 85% NO3. Additionally, low Fe and low P stresses increase the acidification rate. Total dry weights of minus-P plants were about half that of minus-Fe plants. This indicated that plants under P stress had a higher specific rate of acidification than plants under Fe stress.

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Patricia R. Knight, D. Joseph Eakes, Charles H. Gilliam and Harry G. Ponder

Seed geranium (Pelargonium × hortorum Bailey `Scarlet Elite') were grown in subirrigation troughs in 10-cm pots from 25 June to 3 August 1993. Production medium was a 1 pine bark:3 peat moss:1 perlite (v:v:v) mixture. Plants were irrigated using fresh or recycled solutions and fertilized using Peter's Geranium Special 15N-6.5P-12.5K or Osmocote 14N-6.1P-11.6K. Controlled release fertilizer produced greater shoot dry weights and foliar color ratings than plants receiving water soluble fertilizer. Plants receiving a controlled release fertilizer had lower shoot N concentrations than plants receiving water soluble fertilizer. Recycled irrigation solutions reduced plant quality regardless of method of fertilization.

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Dharmalingam S. Pitchay and B.C. Bearce

Petunia and impatiens seedlings were planted in cell packs containing 0%, 25%, or 50% (by volume) coal bottom ash (CBA) mixed with peat: vermiculite. High soluble salts caused fresh and dry weights to be greatly reduced in 25% and 50% CBA. This was thought to be due to insufficient drainage in the shallow cell packs. Subsequent crops were grown in 4-inch pots. Double Pink impatiens in 4-inch pots showed no significant difference between control and ash media in the number of buds and flowers, plant heights and diameters, and fresh and dry weights. For `Mixed Shady Lady' impatiens, the number of flowers, and fresh and dry weights were greater in the control and 50% CBA. Plant heights were reduced in 25% and 50% CBA media. There were no differences in plant diameters among the media. Ivy geraniums showed no significant difference in the number of days from planting to first bloom and 50% florets opening; number of florets, buds, and inflorescences; and stem lengths. Shoot numbers were reduced in 25% and 50% CBA. There was also no significant difference in number of days from planting to first bloom and 50% florets opening, or number of buds and inflorescences for zonal geraniums. Number of florets increased for zonal geraniums in 25% CBA.

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Bridget Behe, Robert Nelson, Susan Barton, Charles Hall, Steve Turner and Charles Safley

Consumers in five U.S. markets evaluated photographs of geranium plants with regard to purchase likelihood. Photographic images were colored electronically to produce uniform geranium plants with five flower colors (pink, white, red, lavender, and blue) and three leaf variegation patterns (dark zone, white zone, and no zonal pattern). Photographs were mounted on cards with five selected price points ranging from ($1.39 to $2.79). We randomly generated an orthogonal array, partial-factorial design for consumers to rate a reduced number of choices. Consumers shopping in cooperating garden centers located in Dallas, Texas; Montgomery, Ala.; Athens, Ga.; Charlotte, N.C.; and Wilmington, Dela., rated 25 photographs on the basis of their likelihood to purchase the plants shown. Conjoint analysis revealed that customers in the Georgia garden center placed the highest proportion of their decision to buy on leaf variegation (29%), while customers in the Alabama outlet placed the most emphasis on price (46% of the decision). Shoppers in Texas valued flower color most highly (58% of their decision to buy). Demographic characteristics and past purchase behavior also varied widely, suggesting diverse marketing strategies for geraniums.

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D.G. Clark, C. Dervinis, T.A. Nell and J.E. Barrett

In this study, the temporal and spatial regulation of putative ethylene receptor genes was examined during ethylene and pollination-induced flower petal abscission of zonal geranium (Pelargonium × hortorum L.H. Bailey). We used the Arabidopsis thaliana ETR1 gene as a heterologous probe to isolate two full-length cDNA clones, GER1 and GER2, from an ethylene-treated geranium pistil cDNA library. Both cDNAs share a high degree of DNA sequence similarity to ETR1, and examinations of deduced amino acid sequences indicate that the proteins encoded by each gene have the conserved ethylene binding and response regulator domains found in ETR1. Experiments focused on determining the temporal regulation of these genes revealed that both genes are expressed in geranium florets much earlier than when the florets become responsive to ethylene treatment, which is sufficient to cause petal abscission in 1 hr. Both genes are expressed in pistils throughout floret development. Experiments focused on determining the spatial regulation of these genes revealed that both genes are expressed at moderate levels in leaves, pistils, anthers, and petals, and are expressed at very low levels in roots. Preliminary evidence suggests that GER2 is transcriptionally regulated by ethylene in pistils after exogenous ethylene treatment. Currently, the transcriptional regulation of these genes in pistils after pollination is unknown.

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J.E. Flaherty, B.K. Harbaugh, J.B. Jones, G.C. Somodi and L.E. Jackson

Bacteriophages specific to Xanthomonas campestris pv. pelargonii (Xcp), the causal agent of bacterial blight of geranium, Pelargonium ×hortorum L.H. Bailey, were isolated from soil and sludge samples from Florida, California, Minnesota, and Utah. Sixteen phages were evaluated for their potential to lyse 21 Xcp strains collected from around the world. The Xcp strains varied in their susceptibility to the phage isolates with 4 to 14 phages producing a lytic or highly virulent reaction. A mixture of five h-mutants was developed from phages that exhibited the broadest host-ranges and tested against the same Xcp strains. The h-mutant phage mixture lysed all 21 Xcp strains. Three experiments were designed to determine the efficacy of using a mixture of four h-mutant phages to control the spread of the bacterial blight pathogen on potted and seedling geraniums under greenhouse conditions. Plants surrounding diseased inoculated plants were treated with a phage mixture at 5 × 108 pfu/mL daily, biweekly, or triweekly, or treated with Phyton-27®, at 2.0 mL·L-1 every 10 or 14 days. In potted geraniums, daily foliar sprays of the phage mixture had reduced disease incidence and severity by 50% and 75%, respectively, relative to control plants after 6 weeks. In two plug experiments, the phage mixture applied daily also had reduced disease incidence and severity by 69% and 86%, and 85% and 92%, respectively, when compared with controls after 5 weeks. In all three experiments, disease incidence and severity were less for plants treated daily with phages than for those treated less frequently with phages or with Phyton-27®. Chemical name used: copper sulfate pentahydrate (Phyton-27®).

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Dharmalingam S. Pitchay, Jonathan M. Frantz and James C. Locke

Geranium (Pelargonium ×hortorum) is considered to be one of the top-selling floriculture plants, and is highly responsive to increased macro- and micronutrient bioavailability. In spite of its economic importance, there are few nutrient disorder symptoms reported for this species. The lack of nutritional information contributes to suboptimal geranium production quality. Understanding the bioenergetic construction costs during nutrient deficiency can provide insight into the significance of that element predisposing plants to other stress. Therefore, this study was conducted to investigate the impact of nutrient deficiency on plant growth. Pelargonium plants were grown hydroponically in a glass greenhouse. The treatment consisted of a complete modified Hoagland's millimolar concentrations of macronutrients (15 NO3-N, 1.0 PO4-P, 6.0 K, 5.0 Ca, 2.0 Mg, and 2.0 SO4-S) and micromolar concentrations of micronutrients (72 Fe, 9.0 Mn, 1.5 Cu, 1.5 Zn, 45.0 B, and 0.1 Mo) and 10 additional solutions each devoid of one essential nutrient (N, P, Ca, Mg, S, Fe, Mn, Cu, Zn, or B). The plants were photographed and divided into young, maturing, and old leaves, the respective petioles, young and old stems, flowers, buds, and roots at “hidden hunger,” incipient, mid- and advanced-stages of nutrient stress. Unique visual deficiency symptoms of interveinal red pigmentation were noted on the matured leaves of P- and Mg-deficient plants, while N-deficient plants developed chlorotic leaf margins. Tissue N concentration greatly influenced bioenergetic construction costs, probably due to differences in protein content. This information will provide an additional tool in producing premium geraniums for the greenhouse industry.

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Serge Gagnon and Blanche Dansereau

Geranium seedlings (Pelargonium ×hortorum Bailey `Smash Hit Red') were given various cold pretreatments (CP) to obtain more rapid adaptation to constant or split-night temperature regimes. The six following CP were used: either 13C or 17/13C for 5, 10, or 15 days. The effect of these CP given at seedling stage was compared with that of control plants held at 17C at night. The CP did not significantly increase the time to first visible flower buds or to anthesis. The number of flowering stems, plant height, shoot dry weight, and leaf area of control plants were not significantly different from plants receiving CP.

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Patricia R. Knight, D. Joseph Eakes, Charles H. Gilliam and Harry G. Ponder

Seed geraniums (Pelargonium × hortorum Bailey `Scarlet Elite') were grown in 10-cm pots in a 1 pine bark : 3 peat moss : 1 perlite medium from 18 March until 5 May 1993. Plants received Osmocote 14N-6.1P-12.5K and either conventional overhead (CO), drip (DI), or subirrigation (SI). Subirrigation produced greater shoot and root dry weights than CO or DI. Plants grown using DI produced fewer branches than plants grown using CO or SI. Plants receiving SI reached anthesis before plants receiving CO or DI. Method of irrigation had no influence on total root, soil, or leachate N, but SI did increase total shoot N.

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Rita L. Hummel, Shiou Kuo, Diane Winters and Eric Jellum

A fish waste/hemlock-fi r sawdust compost (FWC) was evaluated as a container growth medium and N source for the greenhouse production of marigold (Tagetes patula `Queen Sophia') and geranium (Pelargonium xhortorum `Sprinter Scarlet') in 10-cm containers. Treatments were a factorial set of three Douglasfir bark (B)/three FWC mixtures (100% FWC; 50% FWC/50% B; 100% B) and three rates of N fertilizer (0, 300 and 600 ppm N) applied every 2 weeks. After the initial irrigation, plants were drip-irrigated to negate leaching from the containers.

Weekly measurements of leachate conductivity, pH, and inorganic N were made on additional replications of the 0-ppm N plants in all growing media. Plant height and width were measured at 2-week intervals and, at the end of the production cycle, flower number, shoot fresh and dry weight, visual quality, and root dry weight were measured. The growing medium by N interaction was significant for all variables. Results indicated that plants receiving 0 ppm N in 100% FWC were larger and of higher quality than plants in 100% B receiving 600 ppm N. In 100% FWC, marigold shoot growth, dry weight, and quality were not influenced by N rate. The observed geranium and marigold growth response indicated that FWC was an effective N source and growing medium when leaching was minimized with drip irrigation.