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Plantwise Technical Factsheet

Sumatra disease bacterium (Ralstonia syzygii)

Host plants / species affected
Syzygium aromaticum (clove)
List of symptoms/signs
Leaves  -  abnormal leaf fall
Leaves  -  wilting
Leaves  -  yellowed or dead
Roots  -  reduced root system
Stems  -  dieback
Stems  -  internal discoloration
Whole plant  -  early senescence
Whole plant  -  plant dead; dieback
Symptoms
The description of symptoms is based on that given by Bennett et al. (1985).

The disease is often first seen in older trees (>10 years, >8.5 m tall) but younger trees also become progressively affected. Symptoms can be characterized as a progressive wilt and dieback, initially in the crown of the tree to give a 'stag's head' appearance, but eventually leading to complete tree death after 6 months to 3 years. The rate and severity of symptom development appears to be influenced by altitude. Leaves become chlorotic and fall prematurely or may wilt suddenly and remain attached to affected twigs/branches giving a scorched appearance. Older leaves fall first and affected twigs become brown and die back. Early symptoms may be one-sided. The root system may show signs of general degeneration and decay. Greyish-brown streaks may be present in newly formed wood and a bacterial exudate may emerge from the cut ends of discolored vessels.
Prevention and control

Antibiotic therapy has been used to extend the productive life of infected trees but with some phytotoxicity (Hunt et al., 1985). Biological control using avirulent strains of R. syzygii and virulent and avirulent strains of Ralstonia solanacearum has also been reported (Hartati et al., 1991).

No host-plant resistance is known.

Insecticidal control of the insect vector (Hindola spp.) has been suggested as a means of controlling the spread of this disease (Lomer et al., 1990; Stride and Balittro, 1991). Several insecticides applied as foliar sprays have given good protection against Hindola spp. These include cyhalothrin and deltamethrin (Lomer et al., 1990). However, the effectiveness of such a strategy may be limited by the biology of the vector which means that it may transmit the disease even at low population densities (Lomer et al., 1993). Control of the vector would need to be highly effective, quick and persistent to limit the spread of Sumatra disease (Stride and Balittro, 1991).

Impact
Sumatra disease is considered to be the single most important threat to clove production in Indonesia, where cloves are used in the manufacture of Kretek cigarettes. Cloves provide an important supplementary income to many smallholders in Indonesia, and the loss of income resulting from the death of clove trees can have a major impact on local economies. Annual losses in Indonesia were estimated to be £25 million in 1985 (Bennett et al. 1985).
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