| |
New Russian Wheat Aphid! Biotype B
6/6/2003
Ron F. Meyer
Area Extension Agent
(Agronomy)
Colorado State University Extension
Golden Plains
Area |
 |
| I have provided this information to assist you
with making informed decisions. If you have questions about this article or
suggestions on making this or other articles better, please click on the
buttons below. |
|
|
|
By : Frank Peairs, Scott Hailey and Jerry
Johnson
Background
Prairie Red is a Russian wheat aphid
resistant version of TAM 107, which was released by CSU in 1998. It has
become a popular variety in parts of the state with consistent Russian wheat
aphid problems. Resistance in this variety is conferred by the gene Dn4. Other
varieties with this resistance gene include Ankor, Halt, Prowers 99 and
Yumar. Stanton, a resistant variety released by Kansas State
University in 2000, is thought to have a different gene. Combined, these
varieties account for about one fourth of the wheat acres in Colorado in
2003.
Situation
Russian wheat aphid infestations in Prairie
Red have been common this season in southeast and east central Colorado.
Additional reports of infestations in other resistant varieties have been
received from elsewhere in the state. Plants have been observed with heavy
infestations and susceptible symptoms. In the past, plants occasionally had
been observed with heavy infestations, but these plants always showed resistant
symptoms.
Russian wheat aphids were collected from infested Prairie
Red and placed on seedlings of resistant and susceptible varieties in the
greenhouse. We observed a susceptible reaction on all varieties when we used
aphids from infested Prairie Red, but we observed the expected resistant and
susceptible reactions when we used aphids from our greenhouse colony (Table
1).
Our initial conclusion is that there is a new strain (known as a
"biotype") of Russian wheat aphid in Colorado that is virulent to
Stanton and all CSU varieties containing Dn4. There are many questions
that need to be answered about how this might have occurred and what needs to
be done about it.
What we know
1. We have the original biotype
(Biotype A) of the Russian wheat aphid in eastern Colorado and adjacent areas.
This biotype has been observed this season in the field at Fort Collins and
Hays, KS.
2. We have a new biotype (Biotype B) of the Russian wheat aphid.
This is not a completely unexpected development, but there was no way to
prepare for it because we could not identify which resistance sources to use in
new varieties. We recently learned of a different biotype in Chile, and we had
already taken some preliminary steps to prepare for its possible arrival. It is
not known if the Chilean biotypes also is Biotype B.
3. Ankor, Halt,
Prairie Red, Prowers 99, Stanton and Yumar are effective against
Biotype A and susceptible to Biotype B.4.
Biotype B infestations will need
to be managed conventionally on ally Colorado wheat varieties. This means that
the crop will need to be scouted and treated with an insecticide if economic
thresholds are exceeded.
5. Other management tactics such as biological
control and cultural practices should be equally effective against both
biotypes.
6. Russian wheat aphid must be managed with a combination of
management tactics if we are to minimize the development of future biotypes.
Complete management recommendations are available at
http://www.highplainsipm.org/ and
http://www.ext.colostate.edu/pubs/insect/05568.html
What
we don’t know
1. What sources of resistance can we use in future
resistant varieties? There may be genes effective against both biotypes, or it
may be necessary to develop varieties with a combination of genes effective
against both biotypes. Our first test for Biotype B resistance is underway with
over 20 different sources being tested. Several of these sources have already
been used in crossing by the CSU wheat breeding program.
2. Are the two
biotypes different only in their virulence to our resistant wheats, or are
there other important biological or economic differences that might affect
other management recommendations?
3. Where did Biotype B come from? It is
possible that it adapted locally in response to the deployment of resistant
varieties. The other possibility is that it is the result of a new introduction
from another country. Many Russian wheat aphid biotypes are known to exist
elsewhere in the world. Genetic studies by USDA-ARS at Stillwater, OK are
underway in an effort to answer this question.
4. How do we tell the two
biotypes apart? Currently we can collect aphids from damaged resistant
varieties in the field and be fairly certain that we are collecting Biotype B.
Also, we can collect from damaged susceptible plants and test aphids on
resistant seedlings in the greenhouse. However, neither of these procedures
provides the rapid and inexpensive answers we may need to make management
decisions.
5. Will the distribution of Biotype B be different from that of
Biotype A?
Table1. Leaf rolling and plant damage scores for two
Russian wheat aphid biotypes on seedlings of susceptible wheats, Dn4-resistant
wheats and Stanton, May, 2003.
| |
Biotype
A |
Biotype
B |
|
Variety |
Leaf
Rolling1 |
Plant
Damage2 |
Leaf
Rolling1 |
Plant
Damage2 |
|
Akron |
2 |
6 |
3 |
9 |
|
Ankor |
2 |
3 |
3 |
9 |
|
TAM-107 |
3 |
8 |
3 |
9 |
|
Prairie Red |
2 |
3 |
3 |
8 |
|
Yuma |
2 |
7 |
3 |
9 |
|
Yumar |
1 |
2 |
3 |
8 |
|
Halt |
1 |
2 |
3 |
8 |
|
Stanton |
2 |
3 |
3 |
9 |
|
Carson |
3 |
8 |
3 |
9 |
|
Average for susceptible
varieties |
2`.5 |
7.3 |
3.0 |
9.0 |
|
Average for resistant
varieties |
1.6 |
2.6 |
3.0 |
8.4 |
|
1 1 – 3 leaf
rolling scale, where 1 = no leaf rolling and 3 = tightly rolled
leaves.
2 1 – 9 plant damage scale, where 1 = no damage and
9 = dead plant. |
|
Page Created and Maintained by: Perry D. Brewer, Area
Extension Agent (Technology Education/Youth)
6/13/2003 |
|
|
Colorado
State University, U.S. Department of Agriculture, Kit Carson, Phillips,
Washington and Yuma counties cooperating. Extension programs are
available to all without discrimination. Where trade names are used, no
discrimination is intended and no endorsement by Colorado State University
Extension is implied. |
