Can changes in chlorophyll fluorescence be used to determine chilling injury of cold stored feijoa?

Feijoa is a subtropical fruit that has potential for increased export from New Zealand, but its storage life is limited by over-ripening and chilling injury. Physiological indicators that show when plants are experiencing chilling injury before it has become irreversible would be extremely useful, as they would allow remedial steps (such as intermittent warming) to be taken. These indicators would need to be independent of ripening-related changes. Chlorophyll fluorescence analysis (CFA) can be used as an indicator of stress in photosynthetic systems but much remains to be known before application to successfully protect stored products from CI. The objective of this study was to determine if changes in CF could be used to monitor ripening and detect development of chilling injury (CI) of stored feijoa. In the first season of research, a 15% reduction in maximum photochemical efficiency of photosystem II (Fv/Fm ratio) was found during prolonged storage when measured at 2 or 4°C and when fruit were rewarmed after prolonged cold storage the Fv/Fm declined further (0.77-0.656). Data from this season revealed a decline in CF during storage with about 21% of fruit developing chilling injury after 6 weeks of storage for 'Triumph' feijoa. Intermittent warming to 20°C for 24 h after every 6 or 10 d was assessed as a means of preventing CI development. Decline in Fv/Fm was more in fruit exposed to intermittent warming yet the fruit showed less CI. Results from this study suggest that Fv/Fm is not a good tool to assess CI development in 'Triumph' feijoa since the decline in Fv/Fm preceded CI development and appears more closely related to ripening.