Researchers seek grains resistant to barley yellow dwarf
By John O’Connell
ABERDEEN, Idaho — Experiments underway at the University of Idaho’s Aberdeen Research & Extension Center aim to identify the least susceptible wheat varieties to barley yellow dwarf virus — a crop disease that posed major problems in 2013 winter grains.
UI Extension cereals pathologist Juliet Marshall and UI Extension entomologist Arash Rashed will test how quality and yield of four common soft white winter wheat varieties are affected by barley yellow dwarf infection at different growth stages.
The researchers hope to obtain funding from the state’s grain commissions to repeat the experiments for two or three more years, expanding into winter barley and other winter wheat varieties.
Marshall said barley yellow dwarf, which is spread by aphids, has long been present in Idaho but was never widespread here until this season. She estimates 30 percent of 2013 winter grain crops were affected throughout southern Idaho. The disease, which typically reduces yields by 10-20 percent, cut yields in half in some fields.
Symptoms typically surface in the spring and may include severe stunting of the plant and roots, fewer and smaller kernels and yellow or red flag leaves.
Marshall believes warm fall weather without killing frosts into December enabled aphid populations to grow and infect more emerging winter crops last fall.
“That was the biggest epidemic of barley yellow dwarf I’ve seen,” she said.
She believes cold weather has knocked down aphid populations this fall and anticipates less disease next season. Nonetheless, she fears barley yellow dwarf will pose a long-term threat due to the growth in Idaho’s corn acres. Corn is a host plant that supports barley yellow dwarf between wheat crops but shows no symptoms. Some Idaho growers have started spraying their corn for aphids to prevent transmission into winter grain.
Marshall emphasized no winter wheat and barley lines common in the Pacific Northwest have been bred with barley yellow dwarf in mind.
“We are just trying to determine if there’s any resistance available in what we do have,” Marshall said.
Marshall and Rashed are raising barley plants in indoor growth chambers that mimic temperatures and conditions winter crops experience in the field. Rashed infected some of the plants early and will infect others after they have been moved into greenhouses in the spring. A collaborator in California will test infection levels, and grain quality and yield testing will be done in Aberdeen. A control group of plants will measure damage from uninfected aphids.
The researchers have also infested winter wheat grown outdoors, under screens. Rashed is concerned the outdoor experiment may yield inconclusive results as cold temperatures may have killed aphids before they could transmit the disease.
In addition to chemical controls, Rashed advises growers to delay winter wheat planting until after aphid populations have declined, destroy volunteer grass crops and use cultivation to remove green plant material.
In soft white winter wheat, Marshall said the variety Stephens proved to be highly susceptible in fields this season, while it didn’t seem to surface in WB-Junction or SY Ovation. The winter barley variety Charles was also susceptible.