Kirsty Bayliss

According to the Food and Agricultural Organization, more than 800 million people still suffer from hunger, yet one third of food produced (equivalent to $ 1 trillion USD in value) is either lost or wasted globally each year. Postharvest losses are considered a major component of food loss and waste in the food supply chain, from raw production (total harvest) to food consumed. Losses occur due to improper handling, storage, transport, preservation techniques and infection by microorganisms, and can reach up to 45% in fresh fruits and vegetables. Postharvest diseases, particularly of perishable food crops, are predominately caused by fungal pathogens. Management practices for controlling such pathogens include physical, chemical and biological methods in addition to newer technologies such as UV radiation, nano-technology and plasma treatments. Fungicides are the most common management option due to the consistency of results, however, there is increasing demand by consumers for less chemical use, and chemical-free produce can attract premium prices for growers. New technologies are required to reduce postharvest disease losses, without exposing consumers to hazardous chemical residues. This paper reports a novel, non-chemical method for treating postharvest diseases that shows much promise – cold plasma. Our experiments indicate that this method does not have any phytotoxic effects on avocado fruit, but can inhibit pathogens in vitro following an exposure time of 3 min.

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 in vitro efficacy of PAW against Colletotrichum alienum, 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 C. alienum isolate WAC-13891 (1 x 106 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 (250 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.

In vitro studies were undertaken to determine the effects of five chemical fungicide/disinfectant treatments [Tilt 250 EC (propiconazole), Amistar 250 SC (azoxystrobin), Sporekill, (didecyl dimethyl ammonium chloride), Farmcleanse (Alkali metal salts of alkylbenzene sulfonic acid and coconut diethanolamide) and Virkon S (potassium peroxymonosulfate)] in preventing spore germination of Puccinia graminis f. sp. tritici, Kabatiella caulivora, Leptosphaeria maculans and Magnaporthe oryzae. Germination was inhibited by all fungicides and disinfectants. Maximum reductions in spore germination were obtained at manufacturer’s recommended concentration and concentrations above, while concentrations below were less effective than the recommended concentration. Overall, Amistar and Tilt were the most effective of the chemicals tested, reducing germination of M. oryzae L. maculans and P. graminis f. sp. tritici spores by >75%. However, the extent to which germination of fungal spores was inhibited was dependent on the pathogen. Sporekill was the least effective, inhibiting spore germination across all the pathogens by <15%. Additional studies undertaken to define the effectiveness of the same fungicides/disinfectants for the same pathogens inoculated on five common carrier materials, metal, fabric, wood, paper, and rubber, also showed Amistar and Tilt the most effective. Results highlight a necessity for re-evaluating the requirement for decontamination procedures for carrier materials that have perhaps long been mistakenly considered of low biosecurity risk in regards to the movement of exotic fungal plant pathogens and their races.

The Australian grains industry remains free of many pests that cause significant crop losses overseas. While we have many biosecurity systems in place, the large volume of trade and people movement, as well as the ability for pests to enter Australia via natural pathways, means there is always a potential for new pests to establish in crops. Lack of contingency planning can lead to unnecessary loss of property, inappropriate quarantine and loss of valuable time. One of the key tools in industry preparedness of incursions of exotic pests is contingency planning. This project is based on outputs and activities from three separate modules that have a focus on reducing the risk of new exotic pests becoming established. The end-users and beneficiaries of this work will be growers, the grains industry and all parts of the grain supply chain.

This project aims to define the relative likelihood of, and means by which, exotic fungal spore incursions on or in different carrier materials can occur by assessing common pathogen species in Australia and likely entry pathways and develop effective methods of decontamination of such infested materials. In Australia, the risk of inadvertent introduction of exotic fungal pathogen particularly by spores is increasing. Many of these exotic fungal pathogens pose a threat to our agricultural, horticultural and natural ecosystems if introduced into Australia e.g. Ug99. This research will improve the current understanding of the different entry pathways of fungal pathogens to Australia. The research project will specifically focus on the role of different materials as fungal spore carriers and their effects on spore survivability using common fungal spores as a model to develop and apply prototype tools to detect the contamination of carrier materials with exotic fungal pathogen threats, and develop effective methods of decontamination of such contaminated materials.

Quarantine and hygiene are major measures for preventing damage from plant-parasitic nematodes, but there is little information on nematode spread, especially related to rapidly increasing trade associated with globalization. To investigate nematode movement associated with traded plant material, nematodes were sampled from markets of different sizes and types in several countries, together with the origins and destinations of the produce and volumes traded. Nematodes were found consistently on various crops and associated soil. All trophic groups were represented. Markets differed in the distances produce travelled to get there, with some trading mostly local material, others trading mostly material from distant places, and others with a mix of the two. These patterns of movement can be analysed using network models and mapping software to suggest the speed, distance and amount of nematode spread using these pathways. This information will enhance biosecurity and quarantine through better targeting of surveillance and preventative measures.

When grain is harvested and correctly stored it should remain free of infestation from most pests and diseases. Issues only arise when the storage conditions are breached, allowing the entry of pests, water or other contaminants. The hypothesis of this study was that a low level of fungal contamination is always present in healthy stored grain, and that these fungi may be stimulated to grow depending on the temperature at which the grain is stored, the moisture content of the grain, and the duration of storage. Wheat grain at varying moisture contents from 10.4 to 15.2%, was stored for one, two or six months at 15, 20, 25 or 32SC. Gamma-irradiated grain was included as a control. At each harvest time, for each combination of temperature/moisture/storage time treatments, 10 grains were plated on to full strength potato dextrose agar to determine changes in fungal frequency. The number of grains that exhibited fungal growth was recorded , and isolates emerging from the grain were sub-cultured for identification. After one month of storage, the highest percentage of fungal contamination occurred in grain at a moisture content of 11.4 and 13.5% that was stored at 15 and 25' C. After two months of storage, the highest percentage of fungal contamination occurred in grain at a moisture content of 13.5% stored at 25' C. The lowest contamination occurred on grain of 10.4% moisture content stored at 15, 25 and 32.5' C. The most commonly isolated genera were a putative Botryosphaeriaceae (Tiarosporella) that is a likely first report on stored wheat, and Alternaria spp. Most Alternaria spp. were found in grain of 11% moisture content stored at 20°C for one month; however the frequency of isolation of Alternaria sp declined after two months in storage. Nigrospora oryzae and Rhizopus sp. occurred at low frequency. The number of putative Botryosphaeriaceae increased after two months. It is not surprising that fungi can be stimulated to grow on stored grain , particularly when it is stored at high moisture content. What is interesting is the range of fungi that are present, as many of them are capable of producing secondary metabolites such as mycotoxins. Our work is continuing to investigate how the frequency and variation of genera change over time, with the aim of developing a rapid method for early detection of fungal contamination.

Water used for the irrigation of plants has the potential to act as both a source and a means of spread of plant pathogens, yet little research is conducted within this field. This study was conducted to increase our understanding of water-borne plant pathogens in an open irrigation system in Western Australia, particularly in the context of plant biosecurity. It was determined that various Oomycetes and fungal pathogens are present including Phytophthora (multiple spp.), Pythium (multiple spp.), Colletotrichum gloesporioides, Fusarium solani, Fusarium sp., Giberella sp., Leptosphaeria sp., Mortierella sp., Saprolegnia sp., Paecilomyces lilacinus, and various unknown species. The pathogenicity of some of these species has been confirmed on crops grown in the region. There are significant gaps in our knowledge of how these plant pathogens survive and spread in the irrigation system, and very limited information on their ability to cause disease when contaminated water is applied to crops in the region. This study has highlighted the need for new research on the epidemiology and pathogenicity of water-borne plant pathogens, to inform biosecurity risk assessments and develop mitigation strategies.