PATTERNS OF STEM-END ROT DEVELOPMENT IN COOLSTORAGE

Stem-end rots are a major issue for the New Zealand avocado industry, especially as fruit age increases. The impact of stem-end rots in the eyes of the consumer is made worse because of their association with vascular browning. These experiments were designed to determine the effect of time in coolstorage on development of stem-end rots. After 35 days coolstorage at 5.5 o C, Colletotrichum acutatum had grown through the stalk and into the flesh of inoculated avocado fruit indicating that infection can occur before the fruit ripen. The rate of growth of C. acutatum in avocado fruit stems and flesh increased exponentially with time, indicating that as fruit age they become more susceptible to infection. Fruit inoculated with C. acutatum had a reduced storage life of 14 days relative to the uninoculated control. The pattern of stem-end rot development in coolstore was almost identical for inoculated and uninoculated fruit, but the actual amount of disease at any time during storage depends on the amount of disease at the start. This is likely to be related to the amount of inoculum (spores, fungal fragments) in the orchard when the fruit are picked. If the pattern of disease development is consistent for fruit from different orchards, there is potential to develop a predictive model for storability of avocado fruit based on inoculum load in the orchard.