Báo cáo nghiên cứu khoa học " TRISTEZA DISEASE AND ITS MANAGEMENT " pdf

Symptoms of CTV on different citrus species/clone  Citrus tristeza virus CTV caused many different symptoms based on the virus isolates, Citrus variety and the combination of rootsto

TRISTEZA DISEASE AND ITS

MANAGEMENT

NGUYEN VAN HOA SOUTHERN FRUIT RES INST.

It can move from one cell to another through plasmodemata and become systemic infection through phloem tissues and the whole tree got infection.

Potential virus diseases on fruit crops

and its management

 Tristeza virus was considered original from China Tristeza was called as quick decline in America, is the most destructive disease and spread through out the world.

 Only 2 decades after tristeza was introduced from Africa

to South America in 1920s, the disease caused much damaged to citrus industry in Argentina, Brazil and Uruguay Especially on sweet orange grafted on sour orange Virus normally does not express the symptoms

on the resistant combination between rootstock and scion

of mandarin and Trifoliata orange.

Symptoms of CTV on different citrus

species/clone

 Citrus tristeza virus (CTV) caused many

different symptoms based on the virus

isolates, Citrus variety and the combination

of rootstock and scion

 In Asia, many isolates/strains such as seedling yellows (CTV-SY), tristeza (CTV-T), stem pitting - (CTV-SP), and one mild strain Any strain can get infection on one tree or infected by many strains at the same time.

Quick decline, or tristeza disease

The following varieties got infection with quick decline if

it was grafted on sour orange, pumelo or rough

Satsuma and Ponkan group), Tankan, Iyo, Tangor, varieties belonging to tangelo, and grapefruit The tree got infection and shown yellowing and wilt and then die within years If it is grafted on resistant rootstock such as Trifoliate or mandarin, it will be recovered soon

Symptoms

 Seedling yellows

Young seedlings of sour orange, Natsudaidai, rough lemon infected with CTV-SY strain, the canopy become yellow and die If it is grafted in the resistant rootstock it will be recovered quickly

 Stem pitting disease

All most the citrus cultivars infect with the stem pitting strain, even when

it was grafted on resistant rootstock Grapefruit, tangelo, tangor, sweet orange, Iyo, Yuzu and natsudaidai are very sensitive to the disease, even the Satsuma and Ponkan are resistance

The susceptible variety infect show stem pitting on trunk, branches, twigs Infected tree become dwaft, poor development and sometime even died Lead the trees have more flowers but fruit setting less, fruit becomes small, deform Some varieties show brown spots on fruit or fruit with brown spots and gum oozing.

 These trees shown stem pitting on the xylem tissues when the bark removed.

Vein clearing due to CTV

Tristeza disease on citrus

Virus particle under microscopy

Quick decline due to CTV infection

Stem pitting symptoms on the xylem tissues of citrus

Dieback of sweet orange grafted

on sour orange caused by CTV.

Symptoms (cont.)

Inverse pitting, honey

combing, or pinholing

induced by CTV below

the bud union on sweet

orange trees grafted on

sour orange rootstock.

Stem pitting induced by

CTV on small branches of grapefruit

grafted on the tristeza-tolerant rootstock

Citrus limonia.

Stem pitting induced by CTV

on a grapefruit

trunk.

Left: grapefruit from a healthy

tree; right:

four grapefruits from a tree

grafted on sour orange and

infected with CTV.

Vein clearing induced by CTV in inoculated Mexican lime (C

aurantiifolia) seedlings incubated in a glasshouse at 18-25°C.

Symptoms (cont.)

Symptoms of stem pitting on xylem tissue and yellowing on fruit

in the tree system

 The optimum temperature for virus infection and multiplication is 20°C - 25°C

Causal organism: Closterovirus

Virions have a simple construction and consist of a capsid Virions are not enveloped Capsid is elongated and exhibits helical symmetry The capsid

is filamentous, flexuous with a length of 2000 nm and width of 12 nm.

 Quick decline strain occur and cause much damage When it is grafted on sour orange causing dwaft of the tree However, when it was grafted on resistant rootstock, but showing symptomless event when it gotinfection.

Symptoms due to deferent CTV strains

 In some countries, CTV strain can cause stem pitting on any kinds of rootstock.

 The stem pitting showing on the xylem tissues of trunk, branches and twigs Looking from outside, the branches become twisting and bristle The tree become less growth, yield, bear small fruits.

Beed ELISA showing enzyme mediated colour reaction.

Microplate showing Double antibody sandwich-Indirect ELISA results of enzyme mediated reaction of healthy and CTV infected samples.

B and G rows - Buffer control C and E rows - Healthy sample

D and F rows - Infected sample A and H – Empty wells

I

I

H

H

Screening of citrus isolates against CTV by DIBA

From Top No.1 to 14 – Glass house mantained Puna isolates

1 st row - CTV +Ve No 15 to 28 - Glass house mantained Bangalore isolates

2 nd row – Healthy No 29 to 42 - Glass house mantained New Delhi isolates

No 54- Healthy No 43 to 47 - Glass house mantained viroid infected plants

No 55-56 - CTV +Ve No.48 to53 – Field isolates

Electron microscopy showing Decoration of CTV particles by homologous antiserum

Disease transmission

 Virus Tristeza is transmissible through aphid in a semi-persistent manner Aphid can acquire the virus within minutes when

it feed on infected tree and then transmit the virus to the healthy tree within a minutes when it feed on the healthy one.

 Aphid lose their ability of transmission within 24-48 hrs after leaf the infected tree Toxoptera citricida is the most effective aphid in transmission Aphis gossypii of litchi or cucubitae, Aphis spiraecola and Toxoptera aurantii are also transmissible aphids

Toxoptera citricidus – vector transmits sever citrus tristeza virus strain .

Control measures

 When the tree infected with serve strain, there is no way

of cure, so that do not multiply from this tree When on the orchard, there is some randomly infected trees, these trees should be cut off and replant with the free disease seedlings, which have been grafted on resistant rootstock

Even though the aphid can transmit the virus very fast, the chemical or biological control can not reduce the infection speed The transmission speed is too fast, it occur before the control method is conducted However, the control method carried out in the nursery and from the source of scion is very effective

Control measures (cont.)

 The combination of certified scion should be used and the resistant rootstocks such as trifoliate orange, Sunki and Shiikuwasha ( C depressa Hayata) should be used Some of the hybrids as Troyer citrange or Swingle citromelo, are potential rootstock for resistance to tristeza.

rootstock- The free-desased seedlings through STG and heat treatment should be used.

Control measures (cont.)

 Cross Cross protection, protection, the the method method of of inoculation of the mild strain to control the infection of the serve strain, this method has been widely used in South Africa, Australia to fight against quick decline strain and in Brazil to control stem pitting strain

Plants systemically infected with one strain of a virus, will not develop additional symptoms when inoculated with a second strain of the same virus This phenomenon forms the basis of cross-protection tests.

This phenomenon is well known with NEPO viruses Inhibition occurs between closely related strains and generally not between unrelated strains

or viruses.

The mechanism of cross

protection

There are many strategies to explain the mechanism of cross- protection

General theory

same site for replication, which ahs been occupied

by the mild strain so that another strain can not multiply

metabolism.

which can help the tree resistance to the virus.

Theory base on the activities of the coat protein of the VIRUS

CROSS-PROTECTION can not be recommended

as a general practice because:

1 Mild strains also reduced yield upto 5-10%.

2 The immunised crop may act reservoir of virus from where more sensitive spp or varieties can be infected.

3 The mild strain may turn up as sever by mutation.

4 Sever disease may appear with mixed infection of mild strain and unrelated viruses.

Genetic engineering

• The resistant gene from the virus CTV: Coat protein gene, replication gene, etc have been used for transformation