The effect of fruit orientation of postharvest commodities following low dose ultraviolet light-C treatment on host induced resistance to decay

doi:10.1016/j.cropro.2004.12.008

Crop Protection

Volume 24, Issue 8, August 2005, Pages 756-759

https://doi.org/10.1016/j.cropro.2004.12.008 Get rights and content

Abstract

The possibility of inducing resistance to bitter rot (Colletotrichum gloeosporioides), brown rot (Monilinia fructicola), and green mold (Penicillium digitatum) in apples, peaches, and tangerines, respectively, by treating them with ultraviolet light-C (UV-C light) at the stem end in a stationary position without rotation was investigated. This approach was compared with the conventional procedure where fruits were rotated four times, thereby exposing the entire surface area to the full effects of the UV-C light. Results revealed that when the stem ends of apples, peaches, and tangerines were exposed in a stationary position to dosages of 7.5, 7.5 and 1.3 kJ m⁻² of UV-C light, respectively, induced host resistance to postharvest decay which was equal to, or slightly better than when fruits were rotated four different times. When fruits were rotated, exposing only one or two different sides to UV-C light, the percent infection appeared to increase, compared to treating only the stem ends or when fruits were rotated four times.

Introduction

A relatively new crop protection technology that involved exposing fruits and vegetables to low dose hormetic (adj. of hormetin, the agent of hormesis) ultraviolet light (UV-C, 254 nm) has been reported in two reviews, to produce biopositive effects such as induce resistance to postharvest decay (Stevens et al., 1996b; Wilson et al., 1994). This phenomenon is termed radiation hormesis (Luckey, 1980). This contrasts to the germicidal effect of similar UV-C dosage, which showed an inverse relationship between UV-C doses and the amount of propagule of the fungus and number of infected wound lesions found on the surface of a fruits (Stevens et al., 1998).

The development of a hormetic low-dose UV-C on-line apparatus to treat harvested fruits, is being considered as a commercial alternative to chemical fungicide applications to treat fruits to control postharvest decay (Wilson et al., 1997). However, further studies of UV-C application to harvested commodities need to be conducted before a commercial on-line operation can become a reality. At this time the effectiveness and reliability of UV-C treatment needs improvement (Wilson et al., 1997). All postharvested commodities studies in the past have used low hormetic doses of UV-C to induce host postharvest decay resistance, by manually exposing the entire fruit surface to UV-C light by rotating the treated commodities four times (Stevens et al., 1996a, Stevens et al., 1998). This manual rotation system to ensure proper low-dose UV-C coverage to harvested fruits is not practical for an on-line apparatus.

The objective of this study was to determine the effects of only exposing the stem end, and one side (used as a UV-C control) of the fruit in a stationary position without rotation to low-dose UV-C light, to evaluate the effects on induced resistance to bitter rot of apples (caused by Colletotrichum gloeosporioides [Penz.] Sacc.), brown rot of peaches (caused by Monilinia fructicola [Wint.]) and green mold of tangerines (caused by Penicillium digitatum [Sacc.]). These different fruit orientation positions were compared with the conventional four time rotation procedure normally used to treat postharvest commodities (Stevens et al., 1996a, Stevens et al., 1998).

Section snippets

Fruits used

“Elberta” peaches [Prunus persica (L.) Batsch var. Persica] were harvested from E.V. Smith Research Center, Alabama Agriculture Experiment Station Auburn University, Shorter, Alabama. “Golden Delicious” apples (Malus domestica Bork.) were shipped from the Appalachian USDA/ARS Fruit Research Station, Kearneysville, West Virginia. “Dancy” tangerines were (Citrus reticulata Blanco) obtained from Whitmore Citrus Foundation Farm, USDA/ARS, Clearmont, Florida.

UV-C irradiation method

The UV-C application procedure of using a

Results and discussion

Results revealed that when just the stem ends of apples, peaches, and tangerines were treated with UV-C light in a stationary position, they resisted postharvest decay. The results obtained were equal to or slightly better than when the fruits were rotated four times (Table 1, Table 2, Table 3) as required in the conventional orientation method (Stevens et al., 1996a, Stevens et al., 1996b, Stevens et al., 1998). However, when the fruits were not rotated and only one side was exposed or when

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UV-B radiation (UVBR) treatment, previously standardized in our laboratory, contributes to prevent green mold caused by Penicillium digitatum on postharvest lemons. Here, antifungal activity of flavedo extracts from irradiated and non-irradiated lemons was assayed against P. digitatum; also, compounds that could be responsible for this action were searched. The flavedo extracts from UV-B exposed lemons (UVBLE) exhibited a higher antimicrobial activity than extracts from control lemons (CLE). Conidia treated with UVBLE showed a time dependent inhibition of germination and oxygen consumption, a markedly increase in ROS and TBARS production and in membrane permeability. By chemical analysis of lemon extracts, two fractions (A and B) that responded to the irradiation were detected, showing a decrease in Fraction A and an increase in Fraction B. Fraction B showed higher antioxidant and antifungal activities in comparison to Fraction A. Both fractions were complex samples enriched in flavonoids. The specific composition of each fraction could explain the difference in the biological activities, and also the higher efficiency of UVBLE to inhibit in vitro the pathogen compared to CLE. Based on our results, UV-B radiation treatment can intensify natural defenses of flavedo lemon by eliciting phenolic compounds synthesis, among other processes.
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Several attempts with promising results were performed using both organic and inorganic chemicals [8,9,38]. On the other hand, natural resistance in citrus fruit can be elicited by physical treatments, such as heat [20], low temperature [33], UV-C radiation [39], and mechanical injury [6]. The hypothesis of this work was that UVBR induces changes on postharvest lemon peel, representing an acclimation response that enhances fruit resistance against P. digitatum.
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Short communicationThe effect of fruit orientation of postharvest commodities following low dose ultraviolet light-C treatment on host induced resistance to decay

Abstract

Introduction

Section snippets

Fruits used

UV-C irradiation method

Results and discussion

Crop Prot.

Crop Prot.

On the anatomy of the sweet potato root, with notes on internal breakdown

J. Agr. Res.

Penetration of UV-B radiation in foliageevidence that the epidermis behaves as a nonuniform filter

Plant Cell Environ.

Control of development in plants and fungi by far-UV radiation

Physiol. Plantar.

Hormesis with Ionizing Radiation

Short communication
The effect of fruit orientation of postharvest commodities following low dose ultraviolet light-C treatment on host induced resistance to decay