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.