Abstract:
Citrus plants are hosts of several viroid species,
among which, pathogenic variants of
Hop Stunt Viroid
(HSVd) induce citrus cachexia disease. Stunting, c
hlorosis, gumming of
the bark, stem pitting and decline are symptoms of
cachexia in mandarins and their
hybrids as susceptible hosts. Based on the pathogen
ic properties on citrus,
HSVd
variants
are divided in two distinct groups: those that are
symptomless on sensitive citrus host
species and those that induce cachexia disease. In
this study, two cachexia isolates were
selected and biological indexing was performed in a
controlled temperature greenhouse
(40ºC day and 28ºC night) using Etrog citron
(Citrus medica
) grafted on Rough lemon (
C.
jhambiri
), as a common indicator for citrus viroids. The pl
ants were inoculated with the
inocula
from a severe symptomatic tree of a newly declining
orchard of Jiroft, Kerman
province and a mild symptomatic tree from Mazandara
n province. Presence of
HSVd
was
confirmed with sPAGE, Hybridization by DIG-labeled
probes and RT-PCR using specific
primers of
HSVd
. Primary and secondary structures of the isolates
were studied. The
consensus sequence of RT-PCR amplicons of the sever
e isolate (JX430796) presented 97%
identity with the reference sequence of a IIb varia
nt of
HSVd
(AF213501) and an Iranian
isolate of the viroid (GQ923783) deposited in the g
ene bank. The mild isolate (JX430798)
presented 100% homology with the
HSVd-IIc
variant previously reported from Iran
(GQ923784). Both isolates were shown to be cachexia
inducing according to their sizes,
sequences and lack of “non-cachexia expression moti
f” structures.
Keywords
: Biological indexing, Cachexia, Citrus,
HSVd
, Viroid.
