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In vitro efficacy of plasma activated water against Colletotrichum alienum

Kirsty Bayliss: Murdoch University

<div>Cold plasma (CP) has successfully been used for the decontamination of fresh produce from microorganisms, particularly bacteria that cause food safety issues. CP can be used to produce plasma activated water (PAW) which has been demonstrated to have excellent antimicrobial properties. This study investigated the <em>in vitro</em> efficacy of PAW against <em>Colletotrichum</em> <em>alienum</em>, an important postharvest pathogen of avocado. Three volumes of deionised water, 100, 500 and 1000 ml, were treated with CP to generate PAW100, PAW500 and PAW1000, respectively. A conidial suspension of <em>C. alienum</em> isolate WAC-13891 (1 x 10<sup>6</sup> conidia/ml) was then combined with each PAW in a 1:3 ratio (conidia:PAW) and the percentage of germinating conidia were counted after 12, 15, 18, 24 and 36 h of treatment. In addition to treating conidia with freshly prepared PAW, each PAW was also stored for 1, 3, 7 or 15 days (25<sup>0</sup> C in the dark) and the germination tests repeated. All three PAW significantly reduced conidia germination compared to the control, even after 15 days of storage. The effect of PAW100 on conidia ultrastructure showed a significant change in the cell wall, plasma membrane and cytoplasm compared to untreated conidia as observed by transmission electron microscopy. CP technology is now being investigated as an alternative, chemical-free treatment for controlling postharvest rots of avocado.</div>