“Fire blight” is the most devastating disease of apples. Wild apples could help growers fight back.
Using pollen-laden plastic paintbrushes, the team flew among the orchard like bees, fertilizing thousands of white, pink and lavender flowers, and cataloging each new cross, one of which could eventually give birth to a more robust Red Delicious or Honeycrisp. . Part of a USDA funded program initiative To improve fire blight management in five major apple-producing states, the project also fits in with the trend of plant breeders to use the wild relatives of domesticated crops to improve the varieties we eat, an old idea made more feasible by many. new genetic and technical tools.
“It’s very inspiring to watch these apples,” said Khan, standing among the more than 200 different accessions of the apple genus of the orchard. Malus, each made from seeds harvested around the world by generations of apple growers. “But I think sometimes it’s frustrating not being able to take advantage of that diversity. It’s there, it’s beautiful, it’s nice. But how to use it?
Caused by bacteria Erwinia amylovora, fire blight infects trees through new buds or nicks on leaves and branches, which then develop weeping cankers and take on a necrotic reddish-brown color as if they were burnt. If left unchecked, the bacteria will grow just under the bark towards the heart of the tree, killing it. Even if a tree survives infection, it must be cut and removed before an insect or the wind can spread the bacteria to nearby trees. In a bad epidemic – for examplein Michigan in 2000, fire blight can kill hundreds of thousands of trees in an area, wiping out entire orchards. And the threat of fire blight could worsen, with climate change altering the hot, humid weather in which bacteria thrive earlier in the season, when flowering trees are most susceptible. “If you ask an apple grower what they’re afraid of, they’re more afraid of fire blight than anything,” Khan said.
Growers have methods of dealing with fire blight, such as spraying antibiotics or pruning infected branches, but they are often ineffective and come with economic and environmental costs, said George sundin, who does research on fire blight at Michigan State University and leads the USDA fire blight management initiative. The lack of effective controls is compounded by the fact that almost all of the most popular apple varieties are went down from a small family of cultivars susceptible to the disease. Sundin explained that this is probably because fire blight, first reported in a pear orchard in upstate New York in 1780, probably from North America. Thus, apple trees brought by European settlers never had the chance to develop resistance to the disease, which has since become a risk for their genetically similar descendants in orchards around the world. “It’s really like an invasive disease situation in reverse,” he said.
However, some varieties of wild apples, distant cousins of those we eat, have genes that make them resistant or less susceptible to fire blight. By testing the resistance of different species and varieties and then comparing the genetic code of resistant trees, apple growers have identified at least 40 different areas of the Malus genome associated with resistance to fire blight – most of these occur in wild varieties. Khan’s breeding project aims to combine several of these wild genes into an apple line that can resist fire blight without the need for chemicals or other management strategies.