PULLMAN, Wash. — In bad years, microbial disease heavy hitters like fire blight and X-disease phytoplasma cost apple, cherry, and pear growers hundreds of millions of dollars nationally in lost fruit as well as treatment and removal of infected trees.

Joining Washington State University this month as the newly established Endowed Chair in Bacterial Diseases of Tree Fruits, Frank Zhao will study and seek better ways to manage devastating bacterial pathogens in tree fruit.

“We need more tools in our toolbox to deal with bacterial diseases, particularly for organic orchards,” said Zhao, who comes to WSU from the University of Illinois to launch a new, industry-funded research program in tree fruit microbiology.

Growers’ most effective tool has always been antibiotics—chemical drugs that kill bacteria or make it difficult for them to reproduce.

But bacteria can develop resistance that renders antibiotics less or even totally ineffective. In organic orchards, chemicals are often prohibited, raising demand for new techniques.

“Disease outbreaks can be unpredictable in their severity,” Zhao said. “Pathogens change over time—we now know there are at least four different strains of the fire blight pathogen.”

Becoming interested in plant-pathogenic bacteria as a master’s student in China, he has spent his career studying where pathogens come from and how they adapt and survive, most recently the fire blight bacterium, Erwinia amylovora, which has caused serious damage in Pacific Northwest orchards in the past several years, as well as the pseudomonas family of bacteria, which infect a range of crops.

Zhao studies both good and bad microorganisms. Devising strategies to control harmful bacteria with beneficial microbes, he has experimented with nanoparticles as a method to deliver biocontrol agents in orchards. He plans to continue studies of biocontrols and ‘good’ microorganisms at WSU.

Working in the field and the lab, Zhao will screen for and map antibiotic resistance in Washington orchards, identifying the predominant strains of top-priority pathogens such as fire blight and bacterial canker of sweet cherries.

As he begins his efforts in Washington, Zhao will connect with growers to understand their experiences and challenges.

“All these will help me tremendously in getting my program started,” he said. “In turn, I can learn from them and better solve the disease challenges that fruit producers are facing.”

— WSU CAHNRS