Ozonated water combined with heat treatment to control the stem-end rot of papaya

doi:10.1016/j.scienta.2019.108722

Scientia Horticulturae

Volume 257, 17 November 2019, 108722

https://doi.org/10.1016/j.scienta.2019.108722 Get rights and content

Highlights

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Papaya stem-end rot control by heat and ozonated water was investigated.
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The combination of heat and ozonated water in postharvest treatments is effective in controlling stem-end rot of papaya.
•
High temperatures (˃ 60 °C) for short exposure times (up to 30 s) are sufficiently lethal for fungi causing stem-end rot of papaya.
•
Higher efficiency to control stem-end rot of papaya was observed when treatments combined heat and ozonated water.
•
Postharvest treatment using heat combined with ozonated water extended shelf-life of papaya.

Abstract

Stem-end rot is the major postharvest disease of papaya in Brazil, causing significant losses, specially, during long-term transportation and storage. The infection occurs mainly during the flowering period and remains quiescent, without showing any symptom, until the fruit ripening stage begins. The current method of control, using fungicides, has not been effective, besides contaminating the fruit. The aim of the present research was to evaluate the combined treatment using hot water followed by ozonated water to control the disease. The results showed that, as stand-alone treatment, heat and ozone treatment significantly reduced the stem-end rot, controlling around 50% of the severity, and delaying the onset of the symptoms in 3 and 4 days, respectively. A synergistic effect was observed when the treatments were applied combined. The efficacy of the control increased to over 90% and the symptoms onset delayed 7 days. Moreover, the combined treatment delayed the maturation process, increased the PPO activity, and preserved the overall fruit quality, thus extending the shelf life. The integrated approach, combining heat treatment by immersion of peduncle of papaya in hot water at 70 °C followed by immersion in ozonated water (3 mg L⁻¹), controlled efficiently the stem-end rot, therefore being a safe and sustainable alternative for the use of chemicals in postharvest treatment of papaya.

Introduction

Brazil is a great producer of papaya. Around 1400 thousand tons of fruit are produced in 30,372 ha per year, of which 40 thousand tons are shipped abroad, generating a revenue of US$ 40 million (Brazilian Fruit Yearbook, 2018).

Concomitant with the rapid expansion of papaya cultivation in the country is the increase in the incidence of postharvest diseases, especially the stem-end rot, which has become a limiting factor for commercialization, resulting in serious losses. Stem-end rot is caused by a fungal complex composed of Phoma caricae-papayae, Lasiodiplodia theobromae, Colletotrichum gloeosporioides, Fusarium solani (Galsucker et al., 2018; Nery-Silva et al., 2007), and Alternaria alternata (Alvarez e Nishijima, 1987).

The infection by stem-end rot causing pathogens occurs mainly during the flowering period when the pathogen penetrates the stem by natural openings and wounds and remains quiescent, without showing any symptom, until the fruit ripening stage begins. During this stage, the fruit goes through several biochemical and physiological changes, such as an increase in soluble sugar and decrease in fruit natural defense mechanism and phytoalexin levels. This favors the pathogen colonization by changing its nature from an asymptomatic lifestyle to an aggressive necrotrophic form (Galsucker et al., 2018).

The symptom starts with a translucent zone around the peduncle with a margin of water-soaked tissue. In the beginning of the infection process, only a slight browning of the peduncle is apparent. In a few days, the infection takes the whole region, when the tissue becomes black and soft (Alvarez and Nishijima, 1987) rotting the fruit, making it infeasible for consumption.

Currently, there are no effective methods to manage this disease, and consumers worldwide value fruit free of contaminants from clean agriculture. Therefore, the development of alternative technologies, without the use of fungicides for the control of postharvest diseases, such as ozone and heat treatment, is fundamental for the sustainability and maintenance of the productive chain and commercialization of fresh fruits.

Ozone has high oxidation power, being considered the second most powerful oxidizing agent, exceeded only by fluorine, and therefore a biocide with broad antimicrobial spectrum, active against fungi, bacteria and viruses (Khadre and Yousef, 2001). Because Ozone decomposes easily into oxygen after application, it leaves no residues, posing no risk to the consumer whatsoever, and is consequently a clean potential alternative to be used to control postharvest diseases of fruit (Cayuela et al., 2009).

Ozonated water has shown efficient control of postharvest disease in fruits, such as mango (Monaco et al., 2016), plum (Crisosto et al., 1993), apple (Ong et al., 1996), pear (Skog and Chu, 2001), strawberry (Pérez et al., 1999), citrus (Palou et al., 2001 and 2003), guava (Simões, 2012), kiwi (Barboni et al., 2010) persimmon (Salvador et al., 2006), and papaya (Kechinski et al., 2012).

Heat treatment acts directly on the pathogens, removing or destroying spores and mycelium from the fruit epidermis, as well as indirectly, interfering with the physiology of the fruit, retarding the biochemical processes of maturation and senescence, reducing respiratory rate. They also act as inductors of resistance, protecting the fruit against any pathogen attack (Terao et al., 2018).

Our research aimed at evaluating the influence of the temperature in the mycelial growth of the fungi causing stem-end rot of papaya, the efficiency of the treatments using heat and ozonated water on peduncle, applied individually or in combination to control this disease and its influence on the quality of fruit, considering physicochemical parameters, respiration rate, ethylene production and enzymatic activities.

Section snippets

In vitro assays

Isolates of fungi causing stem-rot in papaya were obtained from the Collection of Microorganisms of Agricultural an Environmental Importance at Embrapa Environment in Jaguariúna, São Paulo, Brazil: Phoma caricae-papayae (CMAA 1483), Alternaria alternata (CMAA 1487), Lasiodiplodia theobromae (CMAA 1488), and Colletotrichum gloeosporioides (CMAA 1490). Those fungi isolates were cultivated on Potato Dextrose Agar medium (PDA).

In an attempt to find the lethal combination (temperature × time) for

Influence of heat on mycelial growth of pathogens

The study showed that fungi presented different degrees of thermosensitivity, and the most thermally sensitive was P. caricae-papayae, followed by A. alternata and C. gloeosporioides, which presented intermediate degree, and L theobromae, which presented higher tolerance to high temperatures. Considering the temperature of 52 °C, 60 s was enough to kill P. caricae-papayae, while for A. alternata, C. gloeosporioides and L. theobromae, 150 s, 280 s and 350 s, respectively. were required for the

Discussion

The in vitro test showed that the fungi causing stem-end rot in papaya (P. caricae-papayae, A. alternata, C. gloeosporioides and L. theobromae) have different sensibility to heat, indicating that the most resistant to high temperature is L. theobromae. Therefore, the combination of time and temperature found efficient to control L. theobromae was also efficient to control the other fungi. Regarding the time needed to control such fungi, longer exposure times were required at lower temperatures

Conclusions

The integrated approach combining heat treatment, by the immersion of the peduncle of papaya in hot water at 70 °C for 15 s, followed by the immersion in ozonated water (3 mg L⁻¹) efficiently controlled the stem-end rot. These combined treatments delayed the maturation process, increased the PPO activity, preserving the fruit quality and increasing the shelf life without quality loss, therefore being a safe and sustainable alternative to the use of chemicals in postharvest treatment of papaya.

Acknowledgments

The authors thank the São Paulo Research Foundation (Fundação de Amparo à Pesquisa do Estado de São Paulo - FAPESP: 2018/25318-7) for financial support. To the laboratory technicians Ms Melissa Baccan and Mrs Dagmar Nunes Santos-Oliveira, for their valuable help in gas sampling and chromatography analysis, Mrs Rosely dos Santos Nascimento and Ms Neusa Domingos for physical-chemical analysis. To Biozonne Ambiental for technical support.

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Ozonated water combined with heat treatment to control the stem-end rot of papaya

Highlights

Abstract

Introduction

Section snippets

In vitro assays

Influence of heat on mycelial growth of pathogens

Discussion

Conclusions

Acknowledgments

Food Chem.

Food Chem.

Int. J. Food Microbiol.

Postharvest Biol. Technol.

Food Chem.

Sci. Hortic.

Crop Prot.

Postharvest Biol. Technol.

Sci. Hortic.

Postharvest Biol. Technol.

Postharvest Biol. Technol.

Plant Pathology

Postharvest diseases of Papaya

Plant Dis.

Brazilian Fruit Yearbook

Ripening and quality of ‘Golden’ papaya fruit harvested at different maturity

Braz. J. Plant Physiol.

Introduction to Plant Disease Epidemiology

Control of table grapes postharvest decay by ozone treatment and resveratrol induction

Food Sci. Technol. Int.

Aplicação do Ozônio na indústria de alimentos

Aliment. Nutr.