Approximately 1000 tonnes of Japanese squash (Cucurbita maxima) is exported from Tasmania to Japan each year. Periodically, shipments of squash have been affected by fungal storage rots. Rejection of squash is of concern to the industry as there is potential for significant losses.

In addition the presence of high levels of fungal storage rots can adversely affect the reputation of the product from the State. Acetic acid vapour at concentrations of approximately 5 uL per litre airspace has been shown experimentally to reduce rots caused by several fungal pathogens on a wide variety of fruits. Acetic acid acts by killing spores on the fruit surface. The purpose of this study was to investigate the use of acetic acid vapour as a fumigant for reducing fungal rots of Japanese squash.

Squash (40 per treatment) were places in wooden half-tonne bins and placed in a shipping container of 28.7m3 internal capacity. Fruit were treated with acetic acid vapour at rates of 1, 2, 4, 8, or 16 uL/L of total airspace for either 20 or 40 minutes. Fruit were removed following treatment and stored at 11c along with untreated (control) fruit. Squash were examined at intervals between 7 to 77 days after treatment. Acetic acid treatment had no effect on the number of squash rotted over this period and low concentrations of acetic acid slightly increased the percentage surface area covered by fungal rots.

Acetic acid treatment has no effect or only minor effects on some of the quality attributes of squash (flesh colour, skin colour, weight loss, estimated sugar content, flesh firmness) and did not lead to phytotoxicity. One of the main fungal rots encountered in this study (Fusarium culmorum) often developed as a ring of cottony mycelium from around the stalk or button end of the squash which indicated that it might be developing from inside the fruit.

The presence of fungal pathogens within the squash might in part explain the poor efficacy of acetic acid treatment, which would act as a surface sterilant. Further trail work will be required to determine whether acetic acid will be useful as a commercial fumigant of Japanese squash.

This project has been funded by Hort Innovation, using the research and development levies listed below and contributions from the Australian Government. Hort Innovation is the grower-owned, not-for-profit research and development corporation for Australian horticulture.

• Vegetable Fund