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  • Cornell AgriTech
  • School of Integrative Plant Science
  • Plant Pathology and Plant-Microbe Biology Section

Fire blight costs the U.S. apple industry an estimated $100 million annually in crop losses. New research from Cornell AgriTech may help apple breeders develop resistant varieties and give growers a more sustainable solution in managing the disease. 

Caused by the bacterium Erwinia amylovora, fire blight infects apple trees through flowers or other natural openings, often facilitated by insect transmission.

“It can kill the trees – wipe out an orchard – within a few weeks,” said Awais Khan, professor at the School of Integrative Plant Science based at Cornell AgriTech. “Trees infected by the disease have blackened leaves and a scorched appearance, giving fire blight its name.”

Khan and his team conducted genetic mapping of Malus sieversii – the wild species found in the Tian Shan mountains of Central Asia from which domesticated apples originate – to identify specific genomic regions linked to fire blight resistance. They then developed DNA markers that enable them to screen apple seedlings for fire blight resistance.

Their paper, “Identification and Marker Development of a Moderate Effect Fire Blight Resistance QTL in M. sieversii, the Primary Progenitor of Domesticated Apples,” explains the mapping process and findings. Richard Tegtmeier, Ph.D. candidate in Khan’s lab is the lead author on the paper. The research was funded by the New York State Department of Agriculture and Markets’ Apple Research and Development Program.

The trees used for the research are a cross between the wild M. sieversii and Royal Gala, an apple cultivar that is highly susceptible to fire blight. The M. sieversii used in the cross were grown from the seeds and samples of the wild species collected by the scientists at Cornell during their expeditions to Central Asia in the 1990s. These trees were planted at the USDA-ARS Plant Genetic Resources Unit (PGRU) in Geneva, NY.

“Fire blight resistance was identified in a biparental family of apples developed from a cross of Royal Gala and the wild apples,” Tegtmeier said. He explained that cross-breeding M. sieversii carrying fire blight resistance with good fruit quality apples has the potential to result in a fruit that is fire blight resistant and also appealing to consumers in terms of color, flavor, size and crispiness. 

The researchers developed DNA markers that enable them to screen and select the new generation of apple trees for fire blight resistance when they are young seedlings. “This is a big advantage when the alternative is to wait several years for the trees to be big enough to inoculate with the fire blight and risk killing many of them,” Tegtmeier said. 

He said he is optimistic that with continued breeding efforts and further crosses, fire blight-resistant apple varieties with commercially desirable fruit quality could emerge within the next few decades. “With a few more crosses, it is likely we will start observing fire blight-resistant apples with the fruit quality commercial apples growers would want,” Tegtmeier said. 

Fire blight is found in 46 countries, across four continents. It is prevalent in the U.S. States like New York with warm, wet springs are more heavily affected than states like Washington with drier, less humid springs.

“This research is important to the apple industry because apple growers have to rely on labor-intensive and expensive management practices for controlling fire blight,” Tegtmeier said. “Our work will help breeders develop disease-resistant apples for growers. Genetic defense is sustainable and one of the strongest defenses a grower can have.”

Khan established a new unique orchard at Cornell AgriTech that has approximately 300 diverse M. sieversii types from Central Asia.

“This replicated orchard will facilitate groundbreaking genetic research on disease resistance, abiotic stress tolerance, and superior horticultural and fruit quality traits,” Khan said. He said he welcomes national and global collaborations to maximize the potential of this research orchard over the coming decades.

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