Distinguishing the species - CIMMYT

Aphid-transntitted viral diseases
Aphids are among the most common and
efficient vectors of viral diseases. Disease development
on cereal crops requires infestations of
viruliferous aphids. Normally, small populations
of aphids migrate from neighboring crops or
grasses. Diseased plants occur singly or in small
patches, usually starting at the borders of the
field. Under certain conditions, the aphid population
builds up to the point where extensive windborne
migrations may infest large areas almost
simu Itaneously.
General chlorosis, yellowing and dwarfing
have been considered the typical disease symptoms
of aphid transmitted viruses on cereal crops. I n recent
years, however, cereal crop viral diseases with
mosaic and striping symptoms have been reported
as having aphid vectors.
Barley yellow dwarf virus (BYDV)
This disease is among the most widely distributed
viral diseases on cereals and can cause serious
economic losses. Wheat, barley, oats, rye, triticale
and grasses are hosts of BYDV. Symptom expression
on barley and oats is quite conspicuous-bright
yellowing (on wheat and barley-Figure 221) or
reddening (on oats-Figure 222) of the leaves
starting from the tip and developing toward
the base, stunting, excessive tillering, the development
of white sterile spikes, and the presence of
aph ids are common diagnostic characteristics.
Many species of aphids are vectors for barley
yellow dwarf, but among the most common are
Rhopa/osiphum, Metop%phium and Macrosiphum
species (Figure 223). Schizaphis graminis, the
greenbug, may also transmit the virus (though
somewhat less efficiently) and can also produce
Figure 222. Severe dwarfing, sterility
and a reddish yellow discoloration of
leaves in oats may be due to BYDV.
Figure 221. A wheat leaf showing symptoms of barley yellow Figure 223. Several aphid species serve as common vectors
dwarf virus (BYDV). Notetheyellow,bleached appearanceof of BYDV, including Rhopa/osiphum maidis (shown here).
the leaf. Symptoms are similar on barley (photo S. Fuentes). The main vector by far is R. padi, wh ich is similar in appear·
ance to R. maidis but with reddish hindquarters.
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