MOLECULAR CHARACTERIZATION AND DETECTION OF ONION YELLOW DWARF VIRUS AND AN ALL EXIVIRUS ASSOCIAT ED WITH ONION (ALLIUM CEPA VAR. CEPA L.)
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Date
2008
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Abstract
Onion is an im
portant vegetable crop
throughout the world.
Its productivity in
India is lower than other c
ountries. Though a num
ber of fact
ors are responsible for the
reduced production, viruses are by far one
of the m
ost serious problem
s causing
substantia
l losses.
Onion yellow dwarf virus
(O
YDV) is an im
portant pathogen of on
ion
causing severe losses in onion seed
crop. It belongs to the genus
Po
tyvirus
under the
family
Potyvirida
e
. Onion has also been som
etim
es
found with m
ixed viral infections.
In the present study, coat protein (CP) a
nd P3 protein region of
OYDV and Nucleic
Acid Binding Protein
(NB) region of an
Allexivirus
assoc
iated with Pus
a Red cultivar
of
onion were characterized. The CP of Onion De
lhi PR isolate of OY
DV consisted of 771
nucleotides encoding for 257 am
ino acids. Th
e nucleotide and a
mino acid sequences of
the isolate of OYDV under st
udy were closest to Onion
Nasik isolate of OYDV. It
showed m
ore than 98% identity in
both nuc
leotides and am
ino acids with Onion Nasik
isolate. CP of the isolate under study had
DAG motif having role in aphid transm
ission,
WCIEN box, RQ and AFDF motifs
characteris
tics of poty
viruses were also there.
In
addition to these, two pairs of KD charact
eristic of OYDV and distinct from
other
potyvirus
es were also p
resent.
The partiall
y sequenced P3 region of Onion Delhi P
R
isolate showed identity in the range of
61.4% to 63.8% in nucleotides and 52.7% to
57.8% in am
ino acids indicating that this
region is highly va
riable am
ong
OYDV
isolates. This was the first attem
pt to ch
aracterize the P3 region of OYDV in
fecting
onion in the world. The seque
nce analysis of PCR produc
t of NB region gave 179
nucleotides showing m
axim
um identity
of
72%
with
Garlic virus C
and
Garlic mite
borne virus
both belonging to the genus
Allexivirus
. This is a f
irst k
ind of
inf
orm
ation
on m
ixed infection of OYDV and an
Allex
iviru
s
in onion in the world. OYDV and the
Allex
iviru
s
were detected in the leaves, bulb
s, and anthers of the different cultivars of
onion by RT-PCR and it was found that bulbs are
the better virus source for detection.
Both these viruses could also be detected
sim
ultaneously by duplex RT-PCR in the bulb
of Pusa Red cultivar of onion.
Description
t-7982