Joseph Eyre
University of Queensland

Received the Australian Flora Foundation Young Scientist Award for his poster at The National and Trans-Tasman Horticultural Science Conference ‘Smart Science for Innovative Horticultural Enterprises’ at the Gold Coast International Hotel, Surfers Paradise 21 - 23 July 2008:

Low storage temperatures can induce leaf and flower browning on cut Backhousia myrtifolia stems

Joseph X. Eyre1, Daryl C. Joyce1, and Donald E. Irving2
1The University of Queensland, Centre for Native Floriculture, School of Land, Crop and Food Sciences, Gatton, Qld. 4343, Australia
2Yanco Agricultural Institute, NSW Department of Primary Industries, Yanco, NSW. 2703, Australia.

Cut flowering stems of B. myrtifolia were rejected in the Japanese marketplace in 2004 due to generalised and extensive brown discolouration of both flowers and foliage. This disorder was observed upon outturn following air-freight from Brisbane. Cool chain conditions had been maintained where possible. Tissue browning is a common symptom of low temperature injury in fresh produce, particularly that from the sub-tropics and tropics. The hypothesis investigated was that exposure to low temperatures caused browning of cut B. myrtifolia stems. Similar symptoms were reproduced in 2004 following storage for 1 week at temperatures at or below 10°C. However, the same browning disorder did not appear following repeated storage experiments in 2005 and 2006. Rather, limited brown lesions developed on leaves stored at or below 2°C (2005) or at or below 5°C (2006). Low temperature conditioning at 10°C for 1 or 3 days before transfer to 2°C for the rest of a 1-week overall storage period significantly (P less than 0.05) reduced leaf browning compared to 1 full week at 2°C (control). Nonetheless, the level of leaf browning after low temperature conditioning was still aesthetically unacceptable. Hot water dip conditioning at 45°C for 10 or 20 min also reduced leaf browning, but caused flower browning. Overall, the findings suggest that low postharvest temperature stress can lead to various B. myrtifolia leaf and flower browning symptoms. Variability in symptomology may be attributable to as yet undefined predisposing pre-harvest factors.