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  • Author or Editor: Philip E. Hammer x
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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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Cold storage of cut ‘Sonia’, ‘Royalty’, and ‘Gold Rush’ roses (Rosa hybrida L.) at reduced humidities (50% to 80% RH) significantly decreased the severity of Botrytis cinerea Pers. infections that developed from naturally occurring or experimentally applied inocula, compared to storage at saturated humidity. The disease reduction was attributed to the absence of free water on the petals. Wrapping the flowers in cellophane sleeves before reduced-humidity storage decreased water loss but also impaired disease control. No deleterious effects of reduced-humidity storage on poststorage fresh weight gain or visual quality were observed, whether the wrapped flowers are stored with or without vase solutions. Two biological control agents, the yeast Exophiala jeanselmei and a Coryneform-type bacterium, controlled B. cinerea infections during storage at 2.5°C when applied 0 to 48 hr after inoculation with the pathogen. The level of disease control achieved with the biological antagonists during storage was comparable to that achieved with the fungicide vinclozolin, but the biological antagonists did not control poststorage disease development as well.

Open Access

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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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).

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The effectiveness of fungistatic atmospheres for postharvest control of Botrytis cinerea Pers. infections on cut rose flowers (Rosa hybrids L.) was investigated. Storing cut `Sonia', `Royalty', and `Gold Rush' roses at 2.5C with 10% CO2 for 5 days, followed by 2 days of cold storage in air, reduced the number of B. cinerea lesions that developed on inoculated and noninoculated flower petals by 77% and 82%, respectively, compared to cold storage for 7 days in air. Higher CO2 concentrations and longer CO2 treatment times reduced disease severity further, but resulted in unacceptable leaf discoloration on some cultivars. No deleterious effects of CO2-enriched storage atmospheres on flower quality, weight gain, or vase life were observed. Storage at 2.5C for 7 days in 2 μl SO2/liter reduced B. cinerea infections on inoculated and noninoculated flowers by 53% and 43%, respectively. No deleterious effects on flower quality, weight gain, or vase life were observed. Higher SO2 levels reduced disease severity further, but caused bleaching of the petal margins and necrosis around leaf wounds.

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