The fungal pathogen Penicillium expansum, also known as blue mould, destroys millions of stored apples each year, with estimated 20% post-harvest losses experienced in many countries, including Canada. Meanwhile, developing countries can lose more like 50% of the crop. PBUK examines the latest research coming from Rhiannon Wallace, a PhD candidate at the University of British Columbia, Okanagan, that could have implications for apples stored all over the world.
Wallace’s research has determined that bacteria, originally isolated from cold Saskatchewan soils, may be the answer to preventing mould growth and apple rot while the fruit is in storage or transport.
She has developed a way to stop, or at least control, blue mould, a pathogen that can rot the fruit to its core.
“The majority of postharvest fungal pathogens are opportunistic,” explains Wallace, who is working with UBC Biology professor Louise Nelson. “If a fruit is physically damaged, it is at an increased risk of rotting during storage. So a tiny blemish on the fruit from harvest or handling can turn into a conduit for attack by fungal pathogens and subsequently result in the development of mould.”
Wallace is aiming to cut the amount of post-harvest losses due to blue mould which have traditionally been tackled by using chemical fungicides. However, Wallace says these treatments are less effective as the pathogen has developed resistance, while consumers are increasingly rejecting the use of chemicals.
Does Saskatchewan soil hold the key?
The solution could lie in a particular bacterium specific to Saskatchewan soil, suggests Wallace.
Pseudomonas fluorescens, due to its prairie roots, can survive in cold storage – a characteristic that is key to dealing with cold-stored produce like apples.
Following tests at the British Columbia Tree Fruits Cooperative storage facility, Wallace determined that these bacteria can prevent blue mould from growing on McIntosh and Spartan apples while in storage.
And, the bacteria provided control of blue mould on apples that was comparable to a commercially available biological control agent and a chemical fungicide.
“What is novel about our research is that we show the bacterial isolates we tested have an array of mechanisms to inhibit or kill Penicillium expansum (blue mould) on apples while fungicides generally act only by a single mode,” Wallace adds.
“These findings suggest that the development of resistance by blue mould against our soil bacteria is unlikely.”
She does note that while all three isolates of P. fluorescens tested provided control of blue mould, the level of control provided by each isolate varied with apple variety.
Wallace’s research, supported by the Canadian Horticulture Council and Agriculture and Agri-Food Canada, was recently published in the journal Postharvest Biology and Technology.