Study aims to protect apple trees from fire blight

Scientists have long known that apples have a variety of health benefits. Since they are rich in fiber and antioxidants, they protect against many chronic conditions, such as cardiovascular disease, diabetes, and cancer. Unfortunately, in the past 15 years, increasingly warm and wet weather during the spring has sparked epidemics of fire blight – a disease caused by a bacterial plant pathogen that often leads to the death of trees and causes losses of up to $22 million per year in apple and pear crops in the US. 

Now, a team of researchers from Virginia Tech has received two substantial grants from the United States Department of Agriculture to develop new treatments for this infectious disease.

Fire blight – caused by the bacterium Erwinia amylovora – was discovered at the beginning of the 19^th century and is the first-ever described bacterial disease in the history of plant pathology. This bacterium thrives in warm and wet conditions and usually appears during spring, when the frequent mixture of rain and sun allows it to infect flowers, causing blossom blight. Then, the infection spreads into the shoots and eventually in the wood tissue and trunk of the plant, causing cankers which harbor bacteria that can hibernate during winter (a process called “overwintering”) and spread in the next spring to new flowers.

This disease remains a major challenge for today’s scientists due to a variety of factors, such as climate change, the fact that fruit trees are now planted in high-density orchards, and the bacteria’s ability to spread quickly, and often secretly. Traditional treatments involve spraying the trees with copper-based pesticides in the spring. Unfortunately, although such methods may disinfect the surface of the branches and cankers, bacteria can remain dormant inside.

“No matter how well the growers prune the orchards to take cankers out, there will always be enough cankers remaining in the orchard to allow the bacterium to overwinter and potentially infect again the flowers in the spring,” said project leader Srdjan Acimovic, an expert in Plant Pathology at Virginia Tech. “What I want to do with this research is develop new spray management options that target the bacterium inside of the bark of the cankers and target this stage that has been very poorly investigated in the past.”

In order to more accurately detect bacteria hidden in tree bark, Abramovic has devised a new technology called Droplet Digital (dd) PCR (Polymerase Chain Reaction), which can detect even low amounts of the pathogen and determine how much of the bacteria is present in a canker. 

“This is the latest technology, and we have made many more advances with this research in my lab. We are excited to continue this revolutionary study that we hope will soon benefit our industry partners and stakeholders across the commonwealth,” Abramovic explained.

The grants will also fund two related projects aiming to develop effective dormant copper spray treatments in a mix with bark-penetrating oil to eradicate the bacterium from cankers, assess spray programs with different plant activators which prevent shoot blight and fire blight cankers, and test recently designed antimicrobial enzymes that can degrade the bacterium’s biofilm in order to control blossom and shoot blight.

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By Andrei Ionescu, Earth.com Staff Writer

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