Natural Resistance
Wheat varieties with natural resistance to RWA have
been identified in countries such as Afghanistan, Russia, Iran and Hungary. The mechanisms of resistance to
the aphid vary and in some instances a plant is simply
an undesirable host to the insect while in other instances the plant can negatively affect the insect's fertility
and lifespan. Breeding programs are aimed at incorporating this natural resistance into commercial wheat
lines and the first such wheat lines (Tugela-Dn1) were
released in South Africa in 1992.
Currently, there are 14 different resistance genes
against RWA. Such a repertoire is a valuable resource
for scientists and breeders alike as the aphids very
quickly adapt to plant resistance offered by a single
resistance gene. Releasing new wheat varieties, with
different combinations of resistance genes, is one way
to stay a step ahead of the aphids.
How can science contribute?
Wheat breeding programs aim to incorporate novel
resistance genes or combinations thereof into new cultivars for commercial release. Conventional breeding
practices take time and a lot of manpower though.
Young wheat plantlets to be used in breeding programs are selected based on phenotype (their external
appearance and responses to the environment). This
means that, in order to verify resistance to RWA, thousands of plantlets need to be infested in order to visualize which ones are resistant.
Genetic testing can greatly improve this process. For
example, through the use of high though-put technology, plantlets can be tested by simply collecting a leaf
whereupon hundreds of samples can potentially be
tested for resistance in a single days’ work. The work
done by the Cereal Genomics group involves finding
ways to make these genetic tests less time consuming
and more accurate. At the same time, more about the
aphid and its interaction with wheat is discovered, ensuring that we always have a trump card against this
insect pest. For more information, please visit us at
http://www.cgbase.org.
Russian wheat aphids in South Africa are only females that reproduce asexually. They can produce
many nymphs in a short period of time resulting in
significant population growth. The symptoms of
aphid feeding are visible on the leaf as chlorotic
streaking.