Apple Green Crinkle Disease

Green crinkle apples are shriveled, lumpy and bumpy. Chances are you wouldn’t pick an apple from a tree suffering apple green crinkle disease. Fruit that ugly is unmarketable.  So finding quicker ways to identify the disease is critical to the fruit tree industry.

Granny Smith apples infected with green crinkle disease

Apple green crinkle is a sneaky disease.  Some research indicates it may have an incubation period of three to eight years.

Generally, the disease doesn’t show itself unless there’s a cool spring. When apple green crinkle does show itself it may only affect fruit on two or three branches of the tree.

Scientists aren’t sure what causes the disease, but CPCNW researchers are narrowing down the possibilities.

Scientific studies found that trees with green crinkle disease are infected with three viruses that normally don’t produce green crinkle symptoms.  Those viruses are apple stem pitting virus (ASPV), apple stem grooving virus (ASGV) and apple chlorotic leafspot virus (ACLSV).

Is one of the viruses or all three responsible for apple green crinkle?  Or are the three viruses masking another virus causing the symptoms?

That’s the question graduate student Segun Akinbade is trying to answer in the lab. “When we find out what causes the disease we’ll have the tools we need to help stop it from spreading,” Segun says.

In addition to determining what causes the disease, Segun is working toward developing an effective way to detect the disease before the tree shows symptoms. This will make the propagation of apple trees safer.  The U.S. apple industry will also be able to access new apple varieties form foreign countries faster.

So far they’ve checked apple chlorotic leafspot virus off the list.  Scientists at the National Clean Plant Network center at Washington State University in Prosser used a process known as thermotherapy to eliminate ACLSV from infected trees.  But still the trees had green crinkle disease.

Next, Segun compared the profile of known viruses in two trees that went through thermotherapy.  One of the trees still showed green crinkle symptoms; the other did not. Segun plans to conduct deep sequencing on both the diseased and non-diseased trees.

Deep sequencing allows Segun to compare all of the organisms in the trees.  Hundreds of thousands of sequences will be compared to find the sequences unique to the diseased tree.

“These unique sequences will likely be the ones to blame for apple green crinkle disease,” Segun says.  “This strategy will tell us whether a strain of known viruses is responsible or whether a completely new virus is to blame.”

The National Clean Plant Network is funding this research project in collaboration with researchers at the University of California, Davis and at the Center for Plant Health of the Canadian Food and Inspection Agency in Sidney, British Columbia.