Hot water drenching of 'Hass' avocados for rot control

Sammanfattning: The occurrence of postharvest rots is a major issue for the New Zealand avocado industry, and much research is being carried out to find ways to control them. Since the use of many chemical fungicides and insecticides is being prohibited, there is a constant need for alternative, more environmentally friendly, methods to reduce disorders in fruit. One way to decrease the presence of rots in fruit is to maintain good orchard hygiene prior to harvest. There are also a number of ways to control rots, and their postharvest development. In recent years more attention has been turned towards heat treatments and their potential to reduce the development of rots. The aim of this project was to see whether the incidence of postharvest rots in avocados could be decreased by a hot water drench (HWD) of the fruit after harvest. In September 2002, a project to investigate the efficiency of HWD started in New Zealand. Avocados were drenched in four different water temperatures (44oC, 47oC, 50oC and 53oC) and for different durations (varying between 10s and 80s, depending on temperature), and examined for both external and internal damage after fruit had been stored for 4 weeks. HWD was associated with a range of damage symptoms in avocado fruit. The main form of external damage at higher temperatures and times was heat damage (browning or blackening) of the skin. The internal quality of avocado fruit also decreased with increasing HWD duration and temperature in experiment 1. This was due to increased incidence and severity of body rots and stem end rots (SERs) compared to control fruit. In experiment 2 we found that by treating avocados at high temperatures for short durations the incidence and severity of postharvest rots could be reduced. Treatments found to minimize body rots were 47oC for 50s and 50oC for 10s. The optimum HWD temperatures for minimum body rot severity were similar to those for minimum damage by SER in both experiments. Our results show that HWD treatments at high temperatures for short durations may prove useful as a future postharvest control of rots either alone or in combination with other control measures.