Transcript 幻灯片 1

Section 3 Plant Pathogenic Virus
Definition of virus:
Virus is a special particle usually consisting of nucleic acid
molecule and coat proteins called capsids(衣壳). And can
reproduce itself in suitable host cell.
Common characters:
 Very small (ultramicroscopic), and uncellular organism.
 Containing a kind of nucleic acid (DNA or RNA).
 Depending on their own nucleic acid to multiply.
 Lacking intact(完整的) enzyme and energy system, and
depending on the host cell for energy and all growth materials.
 Obligate intracellular parasite.
1 Shape and structure of virus
 Spherical ---polyhedron(多面体) symmetry;
Bacilliform, linear---helix symmetry.
 Consisting of nucleic and protein. in
addition, including water, mineral element,
lipid, polyamines(多胺) and enzyme system.
Nucleic acid of most virus is RNA.
2 Multiplication
When a virus is introduced into the
cytoplasm of a host cell, the protein coat is
shed(除去) from the nucleic acid and the
nucleic acid core instructs the cell to begin
manufacturing more virus RNA or DNA and
virus coat protein. The RNA or DNA and
protein are manufactured separately and later
assembled in the cytoplasm to form virus
particles. At last, the virus particles are
released out of the cell and infect other cells.
3 Denomination of virus
 Not Latin binomial nomenclature(拉丁双命名法)
 At present, denomination of virus is introducing
popular name method(俗名法), i.e. English name of
host + symptom. e.g. Tobacco mosaic virus.
 Genus name is special international appellation
(名称), i.e. abbreviation of representative host name
+ abbreviation of main character + virus. E.g.
tobacco mosaic virus: Tobmovirus.
4 Foundation of classification
Nucleic acid type of virus---DNA/RNA
Strand number of nucleic acid --- single/double
Whether or not existing lipoprotein envelope
Virus shape
Virus segment (i.e. multipartite)
In addition, virus also can be classified on the
basis of serology (血清学), chemical properties,
vectors, host infected, or combination of these.
5 Main groups of virus
5.1 Tobacco mosaic virus (TMV)
 The TMV particle is rod shaped,
about 300µm long ×15µm in
diameter. The protein subunits
are arranged in a helix around a
spiral core of RNA.
 The virus is one of the most
stable viruses known and can
remain infective for at least 50
years in dead, dried tissues and
for many months on flats,
greenhouse frames, sawdust,
tools, and in the soil.
Tobacco mosaic virus
Typical mosaic symptoms
 There are many strains of TMV. Some cause
severe damage on a given host, whereas other
strains cause such mild symptoms that they are
barely visible.
 Tobacco mosaic virus is transmitted
mechanically. Any means that permit the virus to
touch an injured cell of host plant may result in
infection. One of the most common ways the virus
is spread is by weeding, transplanting, cultivating,
pruning(修剪), or tying(捆绑) operations. Tractors or
equipment that brush against a TMV-infected plant
may spread the virus to other plants.

Tobacco mosaic virus overwinters in a
number of ways; the virus can survive for
years in dried tobacco tissue, also overwinters
in stalk and root tissue of mosaic-diseased
plants from previous crop.
 Tobacco, pepper, and eggplant also are
host of TMV and fruit from these crops may
contain infective virus.
5.2 Cucumber mosaic virus(CMV)
 rounded in profile; 29 nm in
diameter; no envelope(包膜);
without a conspicuous
capsomere(衣壳) arrangement
Cucumber mosaic virus
 Genome consists of RNA; singlestranded; linear. Total genome size
8.621 kb. Genome of three parts.
yellowing and mottling of the older leaves.
Expanding leaves become twisted, curl
downward, Plants are stunted, and fruits
are covered with bumpy protrusions
The cucumber mosaic virus has one of the broadest
host ranges of any of the tomato viruses. The disease
affects a number of important vegetables and
ornamentals including tomato, pepper, cucumber,
squash(南瓜), spinach(菠菜), celery(芹菜), beets(甜菜), and
petunia(矮牵牛花).
The cucumber mosaic virus overwinters in perennial
weeds .The cucumber mosaic virus cannot withstand
dryness or persist in the soil.
Transmitted by an insect; more than 60 spp. including
Acyrthosiphon pisum(豌豆蚜）, Aphis craccivora（苜蓿蚜）
and Myzus persicae（桃蚜）, etc. Transmitted in a nonpersistent manner. Virus also can be transmitted by
mechanical inoculation; transmitted by seed .
5.3 Potato Y virus (马铃薯Y病毒)
 Virions filamentous; usually
flexuous(弯曲的); not enveloped; with a
clear modal length of 750 nm; 11-15 nm
in diameter.
 Virions contain one molecule of
linear positive-sense single stranded
RNA. Virions associated with helper
virus(辅助病毒）, but independent from
its functions during replication ．
Potato Y virus
 the virus mainly infect solanaceae(茄
科), e.g. potato, tomato, tobacco．
Wrinkling of leaves
Tuber necrosis
Many species of aphids are able to transmit PVY,
and one of the most effective vectors is green
peach aphid, Myzus persicae(桃蚜）. Aphids only
need to feed on an infected plant for a very short
time, as little as 20 seconds, to become infected
with the virus.
PVY can be carried from one potato crop to the
next through use of infected seed.
Virus transmitted by mechanical inoculation;
transmitted by grafting(嫁接). Virus does not
require a helper virus for vector transmission and
can help the vector transmission of another virus .