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UBC research looks at ways to control rot in stored apples

Student’s research uses bacteria from Saskatchewan soil to prevent blue mould growth

November 8, 2017  By Marg Land

An example of blue mould growth on a Spartan apple.

An apple a day may keep the doctor away, but the mould on it could destroy the fruit in storage.

Rhiannon Wallace, a PhD candidate at the University of British Columbia’s Okanagan’s campus, has developed a way to stop, or at least control, blue mould. Wallace’s research has determined that bacteria isolated from cold Saskatchewan soils may be the answer to preventing mould growth and apple rot while the fruit is in storage or transport.

“The majority of postharvest fungal pathogens are opportunistic,” explains Wallace, who is working with Louise Nelson, a UBC biology professor.


The fungal pathogen Penicillium expansum, also known as blue mould, destroys millions of stored apples each year. Post-harvest rot can result in yield losses of up to 20 per cent in Canada.

The goal of Wallace’s research is to reduce the amount of produce lost due to post-harvest blue mould. Post-harvest rot is usually controlled with chemical fungicides, but Wallace says these treatments have become less effective as the pathogen has developed resistance and there is consumer pushback to the chemicals.

Wallace suggests the solution may lie in Pseudomonas fluorescens. Due to its prairie roots, the bacterium can survive in cold storage.

During tests conducted at the B.C. Tree Fruits Cooperative’s Okanagan facility, Wallace determined that these bacteria can prevent blue mould from growing on McIntosh and Spartan apples while in storage. In addition, the bacteria provided control of blue mould 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 [blue mould] on apples while fungicides generally act only by a single mode,” Wallace says. “These findings suggest that the development of resistance by blue mold against our soil bacteria is unlikely.”

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