Citrus Tristeza Virus

CITRUS TRISTEZA CLOTEROVIRUS

VIRUS – CLOSTEROVIRIDAE - CLOSTEROVIRUS

Prepared under the FAO Regional Project: Strengthening Quarantine Services for Plant and animal Health in three OECS Countries; Executed by CAHFSA

September 2018

INTRODUCTION

There are three distinct syndromes of CTV infection: quick

decline, stem pitting and seedling yellows. With quick decline

(Fig. 1), the virus affects the cambium layer and blocks the

movement of nutrients and water between the infected

rootstock and the scion. Other symptoms include chlorotic

leaf flecking (Fig. 2), leaf vein clearing, leaf cupping, corking of

leaf veins, thinning of foliage, retarded growth and reduced

fruit size.

Stem pitting occurs in more severe strains of CTV when the

bark is peeled away, and pits in the wood can be observed

ranging from short and narrow to elongated and deep (Fig. 3).

In some cases, gum is associated with the pits and the trunks

may have a ropey appearance. Severely affected trees are

chlorotic, stunted, and generally have low yields of poor

quality fruits (Fig. 4).

Seedling yellows are primarily seen in young seedling in

nurseries. (Fig. 5).

DESCRIPTION

Citrus Tristeza virus (CTV), one of the most serious

pathogens affecting Rutaceae species, causes considerable

economic losses to citrus production worldwide. It is spread

by its insect vector, Toxoptera citricidus. CTV causes

different symptoms on citrus plants depending on the virus

strain, the variety of citrus and the scion-rootstock

combination.

BIOLOGY

The virus particles are located in the phloem of the host plant

where it interrupts its transportation system. The optimum

temperatures for virus infection and multiplication are 20 °C -

Figure 1: Quick decline

Figure 2: Chlorotic leaf flecking and vein clearing

Figure 3: Stem pitting on tree trunk

The virus primarily spreads by sharing of infected budwood.

Quarantine, clean stock, and citrus certification programs

are effective in preventing the introduction of new isolates

of CTV into a citrus area, and in minimizing the spread of

severe CTV isolates within a citrus area.

ENTRY PATHWAYS

REFERENCE(S) Koizumi, M. Citrus Tristeza Virus: Symptoms and Control Food and Fertilizer Technology Center for the Asian and Pacific Region. Accessed on September 22, 2018 at http://www.fftc.agnet.org/library.php?func=view&id=20110714095638 Moreno, P., S. Ambros, M R Albiach-Marti, J. Guerri and L. Pena Maarch 2008. Citrus tristeza virus: a pathogen that changed the course of the citrus industry. Mol Plant Pathol. 2008 Mar;9(2):251-68. doi: 10.1111/j.1364-3703.2007.00455.x. Lee, R. 2015. Chapter Five - Control of Plant Virus Diseases.

Advances in Virus Research. Volume 91, 2015, Pages 143-

173. Accessed on September 22, 2018 at https://

www.sciencedirect.com/science/article/pii/

S0065352714000037

Prepared under the FAO Regional Project: Strengthening Quarantine Services for Plant and animal Health in three OECS Countries; Executed by CAHFSA

BIOLOGY cont’d

25 °C. The quick decline is accelerated by heat and water stress

and can cause shrivelling of the fruits and the leaves to turn

brown.

CTV is transmitted in a semi-persistent manner by some species

of aphids found on citrus plants; primarily the citrus brown

aphid, Toxoptera citricida (Fig. 6) and the Melon aphid, Aphis

gossypii.

The aphid can acquire the virus after feeding on infected plants

for 5-60 minutes but loses the ability to transmit the virus after

24 hours. CTV is also graft-transmitted, but is not transmitted

through seed.

The virus exists in many forms known as strains that vary in the

type and severity of symptoms manifested in host plants. Some

strains are mild and produce no noticeable symptoms.

However, other strains are severe causing decline and death of

the tree or deep pits in the trunk and stem. CTV is phloem-

limited plant virus.

DAMAGE

Tree decline results from necrosis and death (blockage) of the

conductive tissue (phloem) and the resulting depletion of

sugars/starch in the feeder roots which kills the trees. In other

cases, economic loss occurs from the stunting, stem pitting

and low bearing of the infected trees.

REGULATORY STATUS

The Citrus Tristeza Virus is a quarantine pest for Grenada.

CTV is widespread in the Caribbean Region, being

present in Antigua and Barbuda, Aruba, Bahamas,

Belize, Bermuda, Cuba , Dominican Republic, Guyana,

Martinique, St. Lucia, Suriname, Trinidad and Tobago

Figure 4: Yellow spots of fruit infected with CTV

Figure 5: Seedling yellows

Figure 6: Citrus Brown Aphid, Toxoptera Citricida

Citrus Tristeza Virus