Research Shows Promise to Help Growers Better Control Pecan Scab

ARDMORE, Okla. — Noble Research Institute researchers are studying ways to combat the pecan scab disease that decimates pecan orchards every year.

Pecan scab, a disease caused by the fungus Venturia effusa, starts as a small black spot on a leaf and has the potential to reproduce and spread dozens of times throughout the growing season, including to the developing nuts, eventually infecting an entire orchard. Because of its diverse genetic structure, pecan scab becomes resistant to fungicides, causing control issues for pecan growers.

In 2015, Noble Research Institute molecular mycologist Carolyn Young, Ph.D., and Nikki Charlton, Ph.D., senior research associate, set out to determine whether pecan scab reproduces asexually or if it also uses sexual reproduction. The answer could help inform growers on when to spray and use other control methods.

Researchers identified the mating-type genes that most closely matched those found in apple scab, pecan scab’s close cousin, which is known to reproduce sexually. While screening thousands of samples for the genes, Young and Charlton found a concrete sign that pecan scab was a sexually active fungus as both genes were present in the sample population, similar to how both males and females are present in the human population.

The researchers are currently trying to identify the sexual stage in the field to help with pecan scab management in orchards. Once again, they can use apple scab that starts on leaf litter as an example. Researchers will first look on the discarded leaves, shucks and twigs around the tree bases. In fact, getting rid of the dead leaf material may help remove some of the fungus that lies dormant there, potentially preventing the scab from sexually reproducing.

For the full story on this research, check out our Legacy story. To read more about pecans, please visit www.noble.org/campaigns/pecans.

Photos

Carolyn Young, Ph.D., (left) and Nikki Charlton, Ph.D., have found that the pecan scab pathogen (Venturia effusa) has a sexual cycle that may initiate the disease at the beginning of the growing season. By better understanding the pathogen, they and others can work toward providing growers with new ways to manage pecan scab.

The pecan scab fungus starts as a small black spot on the young leaves, shucks and twigs of the pecan tree. Under a microscope, the black lesions can appear fuzzy, which indicates the fungus has cloned itself and started to release tiny bits of baby fungus.

Two isolates of the fungus that causes pecan scab grow in a petri dish as part of a test to understand their mating behaviors. The black is a wild type, the most common form of the fungus. The white type is a natural variant isolated from the wild type.