Effects of Treatment with Electrolyzed Oxidizing Water on Postharvest Diseases of Avocado

Abstract

The present study comprised five trials to investigate the efficacy of postharvest treatment with electrolyzed oxidizing (EO) water on postharvest disease development in avocado. Mature (dry matter 24–34%), hard green fruit cv. Hass (four trials), and cv. Wurtz (one trial) from orchards receiving minimal fungicide sprays were sourced, and subsequently dipped for 30 s in treatment solutions. Fruit were ripened at 23 °C and 65% relative humidity to encourage postharvest disease development, and assessed when ripe for anthracnose and stem end rot (SER), arising from natural field infections and/or the size of lesions resulting from post-treatment inoculation with Colletotrichum siamense. In the case of natural infection, EO water treatment reduced severity of SER disease by 30–75% compared with water treated control fruit in all four trials where it was assessed. Reduction in severity of SER after Graduate A+ fungicide or hypochlorite (NaOCl) bleach treatment ranged from 60–88% or 25–50%, respectively, compared with water controls. Under extremely high anthracnose disease pressure, 20% v/v EO water, NaOCl, as well as Graduate A+ fungicide treatments were mostly ineffective. Treatments in the final trial were applied as overhead sprays in an experimental-scale packing line to simulate commercial conditions. This was the only trial where anthracnose (as well as SER) was significantly reduced in fruit by 20% v/v EO water (12–35%) and Graduate A+ (34%) compared with water control. In two trials with C. siamense-inoculated fruit, anthracnose lesion size was reduced by 68–85%, and 90–100% by 20% v/v EO water and Graduate A+, respectively, compared with water-treated fruit. Fruit firmness and the number of days to ripen were mostly not affected by the treatments. This study demonstrates the potential for electrolyzed oxidizing water to be incorporated into integrated management programs for postharvest diseases of avocado, and possibly other fresh produce.

Stem-end rot in major tropical and sub-tropical fruit species

“…The use of some of the fungicides mentioned above in early literature was banned from use globally in 2001 (List of banned pesticides and pesticide watch list, 2015) or are to be banned from Europe at the end of 2021 (Shimshoni et al, 2019). Recent work suggests that azoxystrobin fungicides or electrolyzed oxidizing water instead of fungicides are effective in controlling SER of avocado (Hassan and Dann, 2019). Prochloraz fungicides are to be banned at the end of 2021 from Europe due to their unfavourable toxicological properties and Fludioxonil, a relatively safer, wide spectrum fungicide has been found to be a suitable alternative for avocado (Shimshoni et al, 2019) and as a postharvest treatment for mango.…”

Extension of Avocado Fruit Postharvest Quality Using Non-Chemical Treatments

“…Overhead spray application of 'Hass' avocados with EOW (20% v/v) reduced the anthracnose incidence to 12%-35%, which was reasonably comparable to that of Graduate A+ fungicide control of 34% [77]. A reduction of 68%-85% vs. 90-100% in lesion size development of anthracnose was observed using EOW and Graduate A+, respectively [77]. Therefore, EOW shows potential to replace the currently used postharvest fungicide Prochloraz ® application.…”

“…A lot of potential efforts still remain towards the postharvest preservation of avocados in a health-conscious manner. Electrolysed oxidizing water (EOW) is among the promising alternatives to synthetic chemicals for postharvest disease and pest management of avocados [77]. The EOW can be simply defined as ionised water solution or electro-activated water with a high oxidation-reduction potential essential for stripping away electrons from microbial cell membranes leading to cell wall collapse [77].…”

“…Electrolysed oxidizing water (EOW) is among the promising alternatives to synthetic chemicals for postharvest disease and pest management of avocados [77]. The EOW can be simply defined as ionised water solution or electro-activated water with a high oxidation-reduction potential essential for stripping away electrons from microbial cell membranes leading to cell wall collapse [77]. Overhead spray application of 'Hass' avocados with EOW (20% v/v) reduced the anthracnose incidence to 12%-35%, which was reasonably comparable to that of Graduate A+ fungicide control of 34% [77].…”

“…The EOW can be simply defined as ionised water solution or electro-activated water with a high oxidation-reduction potential essential for stripping away electrons from microbial cell membranes leading to cell wall collapse [77]. Overhead spray application of 'Hass' avocados with EOW (20% v/v) reduced the anthracnose incidence to 12%-35%, which was reasonably comparable to that of Graduate A+ fungicide control of 34% [77]. A reduction of 68%-85% vs. 90-100% in lesion size development of anthracnose was observed using EOW and Graduate A+, respectively [77].…”