Low temperature conditioning before cold disinfestation improves 'Hass' avocado fruit quality

The potential for low temperature conditioning (LTC) treatments, either alone or in combination with hot water treatment (HWT), to improve the quality of ‘Hass’ avocado (Persea americana Mill.) fruit following cold disinfestation of Queensland fruit flies, was investigated. Avocado fruit were held at 4–8 °C for 3–4 days then disinfested for 16 days at 1 °C before ripening at 16 °C. In a second experiment, fruit were placed in water at 41–42 °C for 15–25 min, either with or without LTC, then disinfested and ripened. In both experiments, LTC at 4 °C for 4 days or at 6–8 °C for 3–4 days increased the percentage of fruit with acceptable external appearance (less than 5% of the fruit with discrete dark patches on the skin, and skin spotting combined) after disinfestation from 0 to 100% due to the effective elimination of discrete patches on the skin. Disinfestation alone increased body rots and diffuse flesh discolouration severity in ripe fruit, while LTC before disinfestation reduced severity of these disorders to similar levels as those in non-disinfested, non-stored fruit. LTC before disinfestation reduced discrete patches severity and improved flesh quality more than HWT. Combined treatments of HWT and LTC before disinfestation were no more beneficial compared with LTC alone. Conditioning of fruit at 6 °C for 3 days followed by disinfestation resulted in no survivors from 50 748 third instars of Queensland fruit fly (Bactrocera tryoni Froggatt). LTC efficacy was verified commercially by conditioning fruit at 6 °C for 3 days followed by disinfestation and airfreight to New Zealand. External fruit appearance and internal ripe fruit quality after disinfestation were found to be high. These results show that LTC before cold disinfestation effectively eliminates skin damage and improves flesh quality of ripe ‘Hass’ avocado fruit, with no negative effect on Queensland fruit fly disinfestation efficacy.