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  • Author or Editor: Wojciech Janisiewicz x
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Restrictions on pesticide usage and the occurrence of fungicide resistant strains of postharvest pathogens have necessitated research for alternative methods of disease control. Psuedomonas cepacia was tested for control of Botrytis fruit rot in strawberry. Results of field applications of P. cepacia were variable. A compound isolated from P. cepacia, identified as pyrrolnitrin, was as effective as Benlate/captan (2,000 ppm) sprays in field applications. Postharvest pyrrolnitrin (100 ppm) dip inhibited growth of pathogens for three days at room temperature. A pyrrolnitrin dip followed by storage at 1°C for five days extended the shelf-life for another five days. Preharvest pyrrolnitrin sprays to `Bristol' black raspberry delayed rot development by 4 to 5 days. Captan (2,000 ppm) treatment provided no protection. In vitro tests showed that B. cinerea isolated from the fruit had developed resistance to captan. These results suggest that the use of a naturally-produced compound might afford another opportunity to reduce postharvest rots without the use of synthetic fungicides.

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Postharvest decay represents major losses in the horticultural industry. Synthetic fungicides are an effective tool in controlling postharvest diseases. However, the need for new methods to control postharvest diseases is emphasized because of resistance to certain fungicides, increased incidence of iatrogenic diseases, health risk concerns, and regulatory constraints on pesticide usage.

The use of biologically derived bioactive substances is an alternative approach for the control of postharvest diseases. For example, pyrrolnitrin, a compound produced by Pseudomonas cepacia, has high antifungal activity toward several pathogenic fungi. Chitosan, obtained from deacetylation of chitin, activates the natural defense mechanism in the host tissue. Some volatile compounds from plants and fruits have fungitoxic properties. Hinokitiol, an extract from Japanese cypress trees, is highly effective in extending the shelflife of peaches. The usefulness and limitations of a number of natural bioactive substances will be discussed.

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The viability of Penicillium expansum Link conidia in sporulating culture declined rapidly when exposed to 38 °C, and when conidia were exposed to 38 °C prior to inoculation of apple fruits (Malus ×domestica Borkh.), the resulting lesions were smaller than those on fruit inoculated with nonheated conidia. `Gala' apples were heated after harvest (38 °C for 4 days), pressure infiltrated with a 2% solution of CaCl2, or treated with the antagonist Pseudomonas syringae van Hall, alone or in combinations to reduce postharvest decay caused by Penicillium expansum. After up to 6 months in storage at 1 °C, no decay lesions developed on fruit that were heated after inoculation with P. expansum, or any combination of P. expansum, antagonist, or Ca. Parallel lots of heat-treated and nonheated fruit that were either infiltrated or not infiltrated with Ca were stored up to 6 months. They were then inoculated with P. expansum alone, or with the antagonist followed by P. expansum. Prior heat treatment did not influence lesion size. Calcium alone, the antagonist alone, and heat plus Ca all reduced the incidence of decay by ≈25%, whereas heat plus the antagonist reduced it by 70%. Calcium plus the antagonist or Ca plus the antagonist and heat reduced decay incidence by 89% and 91%, respectively. The integrated strategy of heat-treating fruit, followed by Ca infiltration and then treatment with an antagonist, may be a useful alternative to controlling postharvest decay with fungicides.

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Blue mold of apples, incited by Penicillium expansum, causes extensive losses on stored apples worldwide. Despite the severity of this problem, apple breeders do not evaluate their crosses for resistance to this disease, because there has been little resistance to blue mold in the gene pool of the germplasm used. A new apple germplasm collection from the center of origin in Kazakhstan, maintained in Geneva, NY, and representing a much broader gene pool, was evaluated for resistance to blue mold. Apples were harvested from the Elite collection trees that were clonally propagated from budwood collected in Kazakhstan and from seedling trees originating from seeds of the same trees as the Elite budwood or from other wild seedling trees in Kazakhstan. Fruit from 83 such accessions were harvested at the preclimacteric to climacteric stage, wound-inoculated with P. expansum at 103, 104, and 105 mL−1 conidial suspension, incubated for 5 d at 24 °C, and evaluated for decay incidence and severity. Two accessions were classified as immune (no decay at 103 and 104 mL−1), four as resistant (no decay at 103 mL−1), 53 as moderately resistant (lesions less than 10 mm at 103 mL−1), and 24 as susceptible. There were positive correlations (r = 0.92, 0.86, and 0.91) between decay severity and all three inoculum levels. Our results indicate a greater genetic diversity among the Kazak apple collection than among cultivated apples as evidenced by their broad range of fruit maturity, quality, and disease resistance patterns. The immune and resistant accessions may serve as a source of resistance in breeding programs and can be useful in explaining the mechanism of resistance to blue mold in apples.

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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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