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C. Stevens, C. L. Wilson, J. Y. Lu, V. A. Khan, E. Chalutz, M. K. Kabwe, Z. Haung, S. Droby, and L. Pusey

Low doses of ultraviolet light (254nm UV–C) irradiation reduced postharvest rots of pome, stone and citrus fruits. Brown rot (Monilinia fructicola) of `Elberta' and `Loring' peaches was significantly reduced by UV–C. Alternaria rot (Alternaria spp.) and bitter rot (Colletotrichum spp.) the principal storage rots of `Golden Delicious apples showed significant reduction following UV–C treatment. Further application of UV–C was effective in controlling green mold rot (Penicillium digitatum) of `Dancy' Tangerines and `Marsh Seedless' grapefruits, stem end rot (Alternaria citri), as well as sour rot (Geotrichum candidum) of `Dancy' tangerines after irradiation.

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J. Liu, C. Stevens, V.A. Khan, J.Y. Lu, C.L. Wilson, O. Adeyeye, M.K. Kabwe, L. Pusey, E. Chalutz, T. Sultana, and S. Droby

The application of low hormetic low-dose ultraviolet light (WV-C, 254 nm) on fruits and vegetables to stimulate beneficial responses is a new method for controlling storage rots and extending the shelf-life of fruits and vegetables. The present study was aimed at treating tomatoes (lycopersicon esculentum) with different UV-C dosages (1.3 to 40 KJ/m2) to induce resistance to black mold (Alternaria alternata), gray mold (Boytris cinerea), and Rhizopus soft rot (Rhizopus stolonifer). Thesediseases were effectively reduced when tomatoes were artificially inoculated following UV-C irradiation UV-C treated tomatoes were firmer in texture and less red in color than the control tomatoes, indicating a delay in ripening. Slower ripening and resistsace to storage rots of tomatoes are probably related. The positive effect of UVC on tomatoes decreased as treatments were performed at stages of increased ripeness.

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C. Stevens, P. L. Pusey, V. A. Khan, J. Y. Lu, C. L. Wilson, E. Chalutz, M. K. Kabwe, Z. Haung, O. Adeyeye, and J. Lin

Low hormetic doses of ultraviolet light (UV-C) stress on exposed peaches (Prunus persica). reduced brown rot resulting from field and artificial inoculation from Monilinia fructicola. To test the hypothesis that UV-C induced resistance through host responses the following tests involving biochemical changes (phenlyalanine ammonia-lyase activity (PAL) and ethylene production (EP)), bioassay of antifungal activity of tissue extracts to the fungus, and latent infection of rot free peaches previously treated with and without UV-C were determined. Exposure of peaches to UV-C dose of 7.5×104 ergs/mm2 promoted an increase in PAL and EP compared to the control. As the PAL activity increased, percent storage rots decreased. Antifungal activity to the fungal conidia in UV-C treated peach extract showed that the percent conidia germination was reduced 3 folds. Preharvest infection of brown rot which indicated latent infection was significantly reduced. To test for the germicidal effect of UV-C on M. fructicola on the surface of peaches, an artificial epiphytic population of the fungus was deposited on the peaches. A negative relationship between UV-C dose of 1.3 to 40×104 ergs /mm2, colony forming units and number of decaying brown rot lesions were found.

Open access

Karl N. Nilsen

Abstract

Although man has effectively accelerated genetic alteration among crop plants in the direction of greater suitability for intensive culture, this has been a comparatively recent and minor genotypic rearrangement as compared to the accumulated contribution of millions of years of prior evolutionary selection. Man's concern with plants has from the beginning been based on their unique photosynthetic capability through which light energy, the ultimate source of life-sustaining free energy, is converted to biologically available chemical energy. In addition, light has been a primary environmental factor within the total regime of selection pressures which have shaped the morphogenic character of plants. It is permissable to anticipate terrestrial plants as responsive in a variety of ways (many yet undescribed) to all wavelength regions of the earth-impinging solar irradiance spectrum. This could be especially true within the shorter wavelength regions (ultraviolet) due to greater photon energies enabling greater possible photochemical and thus greater photobiological activity (39). With the foregoing in mind, how do common light sources vary and is this of any consequence?

Open access

Heidi C. Anderson, Mary A. Rogers, and Emily E. Hoover

the spectral range important for photosynthesis, 400–700 nm ( Björn, 2015 ). The standard films most commonly used in horticultural production transmit lower levels of ultraviolet light, allowing little or no transmission of ultraviolet-B (280–315 nm

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Fouad M. Basiouny and R. H. Biggs

Abstract

Effects of UV-B radiation (280-310 nm) and Zn deficiency on photosynthesis and carbonic anhydrase (CA) activity in peach seedlings (Prunus persica (L.) Batsch) were studied. Low Zn markedly reduced CA activity; however, the reduction was not proportional to the reduction in leaf Zn content. Zn-deficient leaves irradiated with UV-B had lower CA activity, chlorophyll content, spectral reflectance and rates of photosynthesis. The reduction was more pronounced when leaves were distinctly chlorotic. Higher CA activity was not necessary for maintaining high rates of photosynthesis. Target areas in the leaf for UV-B absorption are discussed.

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Abby Pace, Bruce L. Dunn, and Charles Fontanier

, Cupertino, CA). Images were collected before black light exposure (flower mean without ultraviolet) and again while a 365-nm black light was used (Sunlite Industrial Corp., El Monte, CA); the results were reported as the flower mean with ultraviolet light

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C L. Wilson, B. Upchurch, A. El Ghaouth, C. Stevens, V. Khan, S. Droby, and E. Chalutz

An apparatus was designed to deliver low-dose UV-C light to the surface of fruit on a processing line and tested for its control of postharvest decay. It consisted of a row of UV-C emitting lamps mounted on a frame above a conveyer belt that transported the fruit. The dosage of the UV-C light delivered to the fruit surface was regulated by varying the speed of the conveyor belt. Postharvest decay after 28 days storage of `Empire' apples was reduced 52% relative to the untreated checks when the fruit were conveyed at 6.2 m·min−1 (1.38 kJ·m−2 dose) under the UV-C apparatus. Factors affecting the practical application of UV-C irradiation of fruit for controlling postharvest decay are discussed.

Open access

Kristine R. Buckland, Cynthia M. Ocamb, Ann L. Rasmussen, and Lloyd L. Nackley

Widespread outbreaks of tomato powdery mildew (Leveillula taurica and Oidium neolycopersici) are problematic in fresh market tomato (Solanum lycopersicum) crops in western Oregon, USA. In western Oregon, fresh market tomatoes are frequently grown in greenhouses or high tunnels where conditions can promote diseases such as powdery mildew. Heightened concerns about worker safety limit the pesticides available for use in enclosed systems. We studied the efficacy of ultraviolet-C (UV-C) light applications under high-tunnel conditions compared with a standard fungicide program. Plants treated with UV-C had zero incidence of powdery mildew on all sample dates in the first trial. In trial 2, disease incidence was lower on UV-C treated plants than both grower standard and nontreated control early in the study while disease severity remained lower in UV-C than nontreated control and similar to grower standard treatment. Additional research is needed to optimize UV-C treatment intervals to minimize negative effects on plant growth and maximize powdery mildew control.

Free access

Yi hu Dong, Deepali Mitra, Arend Kootstra, Carolyn Lister, and Jane Lancaster

The red color of Royal Gala apple (Malus domestics Borkh.) skin increased in intensity following irradiation with ultraviolet (UV) and white light. The enhanced red apple color was due to an increase in anthocyanin concentration and the increase was dose dependent. High-performance liquid chromatography analysis showed that the composition of flavonoids in UV treated and natural red colored apple skins was similar. The red apple skin color further increased after storage at 4C in the dark. During the course of irradiation the enzymatic activities of phenylalanine ammonia lyase (PAL) and chalcone isomerase (CHI) increased 10-to 20-fold. Northern analysis showed an increase in PAL transcripts during the irradiation treatment, suggesting that the increase in PAL enzymatic activity was due to de novo synthesis of the enzyme in apple skin cells.