Kassala Disease

 

HISTORY, DISTRIBUTION AND IMPORTANCE

Seen for the first time in 1987 in Kassala (Eastern Sudan) and described by Bové (Bové, 1995). The symptoms of affected grapefruit trees are gum impregnations in the bark and mild stem pitting that resemble those of cachexia in mandarin and gummy bark in sweet orange. Symptoms of Kassala disease have also been seen in southern Yemen.

 

NAME OF DISEASE AND SYNONYMS

Kassala disease (Bové, 1995)

Abbreviation: KD for Kassala disease.

 

 

SYMPTOMATOLOGY

 

General aspect of affected field tree

Not reported.

 

Symptoms on trunk (on rootstock and/or scion), limbs and shoots

Scraping the trunk to remove the outer layers of bark, shows the whitish bark tissues to be impregnated with streaks of reddish-brown gum-like material (KD. 01, 02), particularly near the bud union. Bark discoloration affects only the grapefruit scion. Removal of a piece of bark across the bud union is required to see pitting of the grapefruit xylem. After bark removal, the stem pitting observed on affected trees (KD. 03) resembles those of cachexia on cachexia-sensitive hosts and those of gummy bark on sweet orange and rough lemon. However, the amount of gum in the bark seems to be smaller than that seen in the case of cachexia and gummy bark, even though bark gumming can extend up to 2 m above the bud-union.

 

Symptoms on leaves

No specific symptoms.

 

Symptoms on fruit

None.

 

Histological and cytological symptoms

None described.

 

 

CAUSAL AGENT: DESCRIPTION AND PROPERTIES

The graft-transmissibility of the agent has not been studied. The nature of the agent is unknown.

 

 

HOST RANGE

Thus far, restricted to Citrus spp.; non-rutaceous hosts: unknown.

 

Sensitive species, varieties or combinations

The disease was seen on the scions of Foster and Marsh seedless grapefruit trees grafted on sour orange.

 

Symptomless species, varieties or combinations

·  Immune: none described

· Tolerant (symptomless carrier): Sour orange.

 

 

TRANSMISSION      

 

Natural

Cultural transmission through budwood is probable, but not demonstrated.

No evidence for vector transmission.

 

Experimental

Graft transmission has not been demonstrated.

Mechanical transmission: not reported.

 

 

EPIDEMIOLOGY

Not studied.

 

 

DIAGNOSIS

 

Diagnostic field symptoms

Scraping the bark of the grapefruit trunk above the bud union reveals gum deposits (KD. 04). Bark removal across the bud-union shows stem pitting on the grapefruit scion (KD. 05, 06, 07).

 

Comparison with other diseases

After bark removal, affected trees show stem-pitting symptoms resembling those of cachexia on cachexia-sensitive hosts and those of gummy bark on sweet orange (KD. 08).

 

Biological indexing

Not available

 

Serological and molecular diagnostic methods

None available.

 

 

CONTROL

 Use of kassala disease–free budwood.

 

 

 

SELECTED REFERENCES

 

Bové, J.M. (1995). Virus and virus-like diseases of citrus in the Near East region. Chapter 20, The Sudan. FAO, Rome, p 303-318.

 

 

Prepared (2008) by N. Duran-Vila1 and J.M. Bové2

1Centro de Protección Vegetal y Biotecnología

Instituto Valenciano de Investigaciones Agrarias

Apartado oficial 46113 MONCADA (Valencia)

(Spain)

2IBVM, Laboratoire de Biologie Cellulaire and Moleculaire,

I.N.R.A./ Université de Bordeaux 2,

Centre INRA de Bordeaux,

71, Ave. E. Bourleau,

33883 – Villenave d’Ornon,

(France)