Softening of 'Hayward' kiwifruit on the vine and in storage: The effects of temperature

- The softening pattern on-vine and in storage is sigmoidal.
- The portion of the sigmoidal seen in storage depends on the softening rate at harvest.
- Fruit develop a capacity to soften in response to low temperature whilst on the vine.
- This capacity develops 1-2 weeks before the start of faster softening on the vine.
- Temperatures in the region of 8-10 °C can increase the softening rate.

Observations were made on the softening of 'Hayward' kiwifruit on the vine, in storage and in response to low temperatures. The pattern of 'Hayward' softening on the vine and in storage was sigmoidal, as is typical for kiwifruit. On the vine, the initial slow softening rate of 'Hayward' fruit was consistent across seasons, and similar to other cultivars, at ∼2.9 N/week or less. The rate of rapid softening differed among cultivars at 5.9-14.7 N/week. In storage, the initial slow phase of softening was seen only in less mature fruit harvested before any increase in softening rate had occurred on the vine. Maturing 'Hayward' fruit developed a capacity to soften in response to low temperatures 1-2 weeks before the on-vine period of faster softening commenced. There appear to be three aspects of fruit softening to consider in response to temperature: induction of softening at low (e.g. 8-10 °C) but not chilling temperatures, slowing of the biochemical reaction rates that cause softening by lower temperatures (e.g. 4 °C) and chilling by low temperatures close to 0 °C. These findings are discussed in the context of implementing research and the potential commercial impacts from a better understanding of temperature effects on kiwifruit softening.