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Kathleen B. Evensen and Karen M. Olson

Postproduction quality, net C exchange, and petal abscission in response to ethylene were compared following forcing at 21(day)/16C(night) or 18/13C(18-hour photoperiod) of two cultivars of Pelargonium × domesticum L.H. Bailey. Fewer petals of 2- to 6-day-old florets abscised in response to 60 minutes of 0.7 μl ethylene/liter on plants forced at low temperature than on plants forced at 3C higher temperature. Forcing temperature did not affect floret longevity or the number of florets opening during forcing, but the floral display under simulated consumer conditions was prolonged in low-temperature plants by the continued development of buds. Dark respiration rates at 21C were lower in leaves from plants forced at low temperature than in leaves of plants forced at the higher temperature. Differences in postproduction quality between plants forced at high and low temperatures may have been related to the reduced rate of carbohydrate depletion in low-temperature plants.

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David G. Clark and Kathleen B. Evensen

Ethylene-regulated gene expression is being studied in several plant systems, but the exact mechanism of ethylene action during plant development and senescence is poorly understood. When geranium (Pelargonium Xhortorum) flowers are exposed to 1 μ1/L of ethylene gas for 1 hour, petals begin to abscise within 60-90 minutes from the start of treatment, The rapidity of the response implies that it must be very direct. We now demonstrate that ethylene acts at the level of message accumulation. We have constructed a cDNA library from mRNA isolated from ethylene-treated geranium gynoecia. Ethylene-induced clones have been isolated by differential screening of this library with cDNA probes synthesized from ethylene-treated and untreated geranium gynoecia mRNA. Identification and characterization of these clones will be discussed.

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Philip E. Hammer and Kathleen B. Evensen

We studied the effects of environmental conditions during production on susceptibility of roses to postharvest infection by B. cinerea. For flowers harvested from a commercial greenhouse, susceptibility was linearly correlated (r = 0.97) with mean air velocity during the 5-week periods before each harvest. Susceptibility was also correlated with mean leaf to air temperature gradient (r = 0.83) and inversely correlated with wetness measured on an electronic leaf (r = -0.92), but these correlations were interpreted as secondary effects of the correlation with air movement. Susceptibility was not correlated with temperature, relative humidity (RH), or the other factors measured. In growth chamber experiments, flowers grown under high wind speed (0.55 m·s-1) were significantly more susceptible to infection than flowers grown under low wind speed (0.18 m·s-1). High relative humidity during production increased background infection levels (i.e., those infections not caused by laboratory inoculation) but did not affect susceptibility.

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Kristian Borch, Kathleen B. Evensen, and Jonathan Lynch

Impatiens (Impatiens × hybrida `Impulse Orange'), and marigold (Tagetes × hybrida `Janie Tangerine') plants grown under low phosphorus were more resistant to drought stress than plants grown with a conventional, high-P fertilization program. Low concentrations of P were supplied using alumina-buffered P incorporated into the peat media. Alumina was charged with two levels of P, giving two levels of P-desorption. The alumina-buffered P amendment amounted to 2% by volume of the medium. Control plants (high-P treatment) were fertilized with a nutrient solution containing a P concentration of 1.5 mm. Phosphorous leaching was reduced by 96% to 99.4% in the low-P treatments compared with controls. Low-P plants showed no signs of P deficiency or aluminum toxicity. Impatiens plant diameter was significantly reduced by low-P fertilization, and leaf area was reduced by low P in both species. In marigold plants, roots were confined to a small volume beneath the drip tube in high-P plants, while in low-P plants they were well distributed through the medium. Impatiens roots showed no obvious differences in root distribution. Plants at the marketing stage were exposed to drought. The low-P plants of both species wilted more slowly and recovered more quickly when irrigated than the high-P controls. The reduced leaf area on the low-P plants may account for the improvement in drought tolerance.

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Kathleen B. Evensen, Joseph M. Russo, and Harriet Braun

Grading criteria are proposed for judging potatoes (Solanum tuberosum) for chip quality and yield. The criteria were derived from a decision-making scheme developed from expert opinions, U.S. Dept. of Agriculture grades, and a statistical evaluation of stored potatoes. The criteria are presented as ranges of acceptable values for a limited set of variables found to be important for chip quality and yield. These variables include bruising, cracks, cuts, fusarium dry rot, lesions, and scab. The proposed criteria, besides being a practical decision-making tool for processors, could serve as a knowledge base for potato expert systems and the development of mechanized sorting equipment.

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Philip E. Hammer, Kathleen B. Evensen, and W.J. Janisiewicz

Pyrrolnitrin, an antibiotic isolated from Pseudomonas cepacia, was used for postharvest control of B. cinerea infections on cut `Sonia' and `Royalty' rose flowers. Pyrrolnitrin was applied as a bud dip and followed by inoculation with B. cinerea conidia. Dip treatments of 12 to 200 mg·liter-1 pyrrolnitrin significantly reduced disease severity during storage at 2C and promoted post-storage fresh weight gain (an index of cut flower quality). No phytoxicity was observed on leaves or petals at concentrations of up to 200 mg/liter. Dip treatment with 100 mg/liter pyrrolnitrin reduced disease severity to <10% of that on control flowers and prevented post-storage flower rot. This level of disease control was comparable to that achieved with 1800 mg/liter vinclozolin.

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C. Fred Deneke, Kathleen B. Evensen, and Richard Craig

The postharvest quality of regal pelargoniums [Pelargonium × domesticum L. H. Bailey] is limited by petal abscission. Cultivars that have diverse postharvest longevities were selected to study ethylene sensitivity and endogenous ethylene production. Petals of both intact and detached inflorescences abscised in response to low dosages of exogenous ethylene (0.5 μl·liter-1 for 1 hour). Ethylene sensitivity varied among cultivars and increased with floret age. Silver thiosulfate reduced ethylene sensitivity and often extended floret longevity beyond that of the controls. A climacteric-like rise in endogenous ethylene production occurred in excised gynoecia (including the receptacle) as floret age increased from 1 to 12 days postanthesis. Ethylene production increased a few days earlier and achieved a higher maximum rate in `Parisienne' than in `Virginia'; `Parisienne' also abscised petals earlier. Relatively low levels of endogenous ethylene may regulate petal abscission, since inflorescences were very sensitive to exogenous ethylene, and increased endogenous ethylene production preceded petal abscission.

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C. Frederick Deneke, Leon J. Glicenstein, Kathleen B. Evensen, and Richard Craig

The postproduction quality of 33 cultivars and 178 Pennsylvania State Univ. breeding lines of Pelargonium ×domesticum L.H. Bailey was evaluated in a simulated consumer environment. Petal abscission was the primary factor that reduced postproduction ratings (PPR). The heterozygosity of some cultivars was indicated by the range of PPR of progeny from self-pollinations. This range of PPR implies that P. ×domesticum has genetic variation for postproduction quality that can be used in a breeding and selection program. Few progeny with high PPR were produced from either self- or cross-pollinations involving parents with low PPR. Many of the superior progeny resulted from parents with high PPR. Therefore, progeny with improved postproduction quality can be developed by selecting parents with high PPR.

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Barbara L. Goulart, Philip E. Hammer, Kathleen B. Evensen, Wojciech Janisiewicz, and Fumiomi Takeda

The effects of preharvest applications of pyrrolnitrin (a biologically derived fungicide) on postharvest longevity of `Bristol' black raspberry (Rubus occidentals L.) and `Heritage' red raspberry [R. idaeus L. var. strigosus (Michx.) Maxim] were evaluated at two storage temperatures. Preharvest fungicide treatments were 200 mg pyrrolnitrin/liter, a standard fungicide treatment (captan + benomyl or iprodione) or a distilled water control applied 1 day before first harvest. Black raspberries were stored at 18 or 0 ± lC in air or 20% CO2. Red raspberries were stored at the same temperatures in air only. Pyrrolnitrin-treated berries often had less gray mold (Botrytis cinerea Pers. ex Fr.) in storage than the control but more than berries treated with the standard fungicides. Storage in a modified atmosphere of 20% CO2 greatly improved postharvest quality of black raspberries at both storage temperatures by reducing gray mold development. The combination of standard fungicide or pyrrolnitrin, high CO2, and low temperature resulted in more than 2 weeks of storage with less than 5% disease on black raspberries; however, discoloration limited marketability after≈ 8 days under these conditions. Chemical names used: 3-chloro-4-(2'-nitro-3'-chlorophenyl) -pyrrole (pyrrolnitrin); N-trichloromethylthio-4-cyclohexene-l12-dicarboximide (captan); methyl 1-(butylcarbamoyl) -2-benzimidazolecarbamate) (benomyl); 3-(3,5 -dichlorophenyl) -N-(l-methylethyl -2,4-dioxo-l-imi-dazolidinecarboxamide (Rovral, iprodione).