Faster ID of Wheat Resistant to BYD
Agronomist Herbert Ohm (left) and molecular biologist Joe Anderson inspect the
heads and leaves of wheatgrass plants in which a chromosome for resistance to
barley yellow dwarf virus (BYDV) was identified for breeders wishing to
transfer it into new wheat varieties.
A more rapid way to screen for wheat that contains a disease-resistance gene
borrowed from a wild relative has been developed by
Agricultural Research Service
Joseph M. Anderson, a molecular biologist at the ARS Crop Production and
Pest Control Research Laboratory in West Lafayette, Indiana, worked with Purdue
University researchers to find a rapid genetic test for resistance to barley
yellow dwarf virus (BYDV). Their research may help plant breeders more quickly
develop resistant crop varieties.
And the faster the better--because the virus continues to attack small
grains worldwide, including wheat, rye, barley, and oats.
The virus is carried by aphids that inject it into the plant as they feed.
Infected plants develop yellow leaves and become dwarfed or stunted. Yield loss
varies widely--from 5 to 80 percent. While barley and oats have some natural
resistance to the virus, domestic wheat varieties contain none.
Hoping to genetically add BYDV resistance to wheat, Purdue University
agronomists Hari C. Sharma and Herbert W. Ohm transferred a chromosome from
wheatgrass into wheat plants. Wheatgrass is naturally resistant to this virus.
But the problem with this approach, the scientists say, is that an entire
wheatgrass chromosome is too much.
With the new PCR test, molecular biologist Joe Anderson is able to examine
chromosomes of a BYDV-resistant wheat plant and specifically identify those
that conferred the resistance.
"The whole chromosome may affect other properties of wheat, such as
grain yield and milling and baking quality of the flour, or it may increase the
time from planting to harvest," Anderson says. "We want to use only
enough of the chromosome to get the disease resistance."
Finding the right amount of chromosome has been difficult. Traditional
methods of screening for specific genetic traits included visually examining
plants for desired traits. But that didn't tell scientists enough about the
plant's genetic makeup.
Other, more time-consuming methods--such as additional crossbreeding and
culling of weaker hybrids and testing for virus resistance through aphid
inoculation and antibody activity--were needed to determine which plants
displayed the desired traits.
Ultimately, to identify those wheat lines that contained a small piece of
the wheatgrass chromosome, laboratory technicians had to use complex molecular
biology techniques to examine their chromosomal structure. Once they identified
plants containing fragments of the chromosome, they then used those lines to
develop resistant varieties. The process typically took several years and
wasn't always successful.
To speed it up, ARS scientists devised a polymerase chain reaction (PCR)
test that used a molecular marker--a piece of genetic material, or DNA, from
the wheatgrass chromosome--to distinguish plants with a piece of the
Use of the PCR test to show which plants contain wheatgrass DNA and then
characterizing these plants genetically has greatly increased the accuracy and
frequency of finding the plants with just a portion of the wheatgrass
chromosome, says Anderson.
"In this case, we've had success 33 percent of the time using PCR
testing, versus 4 percent with older methods," he says. "This test is
very fast. It allows us to determine in just a few hours whether a plant
contains the desired DNA."
The bright yellow of wheat leaves infected with barley yellow dwarf virus
contrasts sharply with the deep green of normal, healthy wheat.
Here's how the test works. After scientists find a sequence of DNA located
near the disease-resistance gene, they clone, or copy, it and then take
segments to use in the PCR test. These DNA segments are added to DNA of plants
the scientists think might be carriers of the wheatgrass chromosome with the
BYDV resistance trait. Since these segments will bind only to the DNA of the
wheatgrass chromosome, scientists know that when that happens, they have
detected wheatgrass DNA in a wheat plant.
Using this rapid technique, Anderson and his coworkers have identified
several wheat lines that are virus resistant and carry only a small portion of
the wheatgrass chromosome. These lines are currently being incorporated into
the Purdue University wheat-breeding program to develop high-quality
BYDV-resistant wheat varieties.
"The beauty of this PCR test is that it can also be used to select
virus-resistant lines without going through the very time-consuming,
labor-intensive, and expensive inoculation and antibody testing that was
required in the past," says Anderson.
The upshot: more rapid selection of potentially resistant elite lines by
"We can easily screen several hundred samples in a day using the PCR
test, compared to 100 samples in 3 or 4 weeks," Anderson says.
Faster identification of plants with disease resistance also means more
field samples can be screened.
"We can have faster and more accurate evaluation of actual varieties
growing in the field using rapid testing. This is a significant change over the
traditional methods that required two or more seasons of crop growth before we
could determine which plants to include in subsequent breeding
Lyons-Johnson, Agricultural Research Service Information Staff.
Joseph M. Anderson is at
Crop Production and Pest Control Research Laboratory, Lilly Hall of Life
Sciences Building, Purdue University, West Lafayette, IN 47907; phone (765)
494-5565; fax (765) 496-3452.
"Faster ID of Wheat Resistant to BYD Virus" was published
in the June 1998 issue of Agricultural Research magazine. Click
here to see this issue's table of