Citrus sudden death is a new disease in Brazil: addition to the EPPO Alert List
Citrus sudden death is a new lethal disease of unknown aetiology which has recently emerged in Brazil. First symptoms were observed in 1999 in Minas Gerais (in Triangulo Mineiro), and then spread to northern São Paulo which is a major citrus-growing area. It is estimated that 500 trees were affected in 1999, 300,000 at the beginning of 2002, and that the disease has killed approximately 1 million citrus trees within 20 months. Spatio-temporal studies suggested a biotic cause for the disease (possibly a vector-borne pathogen). So far, all attempts to detect fungi, bacteria, phytoplasmas and viroids failed. As the symptoms observed are similar to the quick-decline form of Citrus tristeza closterovirus (CTV – EPPO A2 quarantine pest), it is suggested that a particular strain of CTV could be involved in this lethal disease.
Citrus sudden death (a lethal citrus disease of unknown aetiology)
Why: Citrus sudden death came to our attention because it is a new disease which has led to the death of approximately 1 million citrus trees in Brazil. An important campaign has been launched in Brazil to control this lethal disease and start research programmes. The cause of citrus sudden death remains unknown but a pathogen is suspected.
Where: Brazil (Minas Gerais, São Paulo).
On which plants: Sweet orange (Citrus sinensis cvs. Baia, Baianinha, Hamlin, Natal, Pera, Rubi, Rio, Westin, Pineapple, Valencia), mandarins (C. reticulata cv. Cravo, Ponkan), tangelos (Citrus x tangelo cv. Orlando), all grafted on Rangpur lime (C. limonia). So far, the disease has not been seen on mandarins (C. reticulata cv. Cleopatra, C. sunski), on citrumelo (Poncirus trifoliata x C. paradisi cv. Swingle) or on Poncirus trifoliata rootstocks. In Brazil, because of the presence of Citrus tristeza closterovirus (CTV – EPPO A2 quarantine pest) and the considerable losses it caused in the 1930-40s, 85 % of citrus trees are now grafted on Rangpur lime (C. limonia) which is a CTV-resistant rootstock.
Possible cause: Spatio-temporal studies suggested a biotic cause (possibly a vector-borne pathogen). Remarkable similarities with spatial patterns presented by CTV-infected trees in the presence of its most efficient aphid vector Toxoptera citricida were observed. So far, all attempts to detect fungi, bacteria, phytoplasmas and viroids failed, only CTV was detected in symptomatic trees (as well as in asymptomatic trees) by using electron microscopy, serology, and comparison of dsRNA patterns. Finally, symptoms observed are similar to the quick-decline form of CTV. Therefore, it is suggested that a particular strain of CTV could be involved in this lethal disease.
Damage: Initial symptoms are a generalized foliar discoloration. Affected trees show partial defoliation, fewer new shoots, absence of internal shoots, and finally die. Fruits are usually normal, but remain attached to the dying or dead trees. Death of large portions of roots is observed. A yellow stain can develop in the phloem of C. limonia. Trees can be killed within 1 to 12 months after the first appearance of symptoms.
Pictures can be viewed on Internet (http://www.fundecitrus.com.br/msubita.html).
Transmission: Unknown, but spatio-temporal studies suggested that vectors could be involved.
Pathway: If the causal agent is indeed a particular strain of CTV, a possible pathway could be: Citrus plants for planting from infected regions in Brazil (but normally this pathway is closed), fruits with leaves and peduncles, viruliferous vectors.
Possible risks: Citrus are important crops in Mediterranean countries mainly for fruit production but also for ornamental purposes. The risk of establishment of this particular CTV strain (if this hypothesis is verified) is difficult to predict as the Mediterranean epidemiological situation differs from the Brazilian one: in the Mediterranean region most sweet oranges are still grafted on sour orange rootstocks (C. aurantifolia) and the most efficient vector Toxoptera citricida is broadly absent. However, as the disease is so devastating in Brazil, precautions should be taken not to introduce it into the EPPO region.
EPPO RS 2003/090
Panel review date - Entry date 2003-06
Sources
Bassanezi, R.B.; Bergamin Filho, A.; Amorim, L.; Gimenes-Fernandes, N.; Gottwald, T.R.; Bové, J.M. (2003) Spatial and temporal analyses of citrus sudden death as a tool to generate hypotheses concerning its etiology. Phytopathology, 93(4), 502-512.
ProMED postings of 2003-03-20 & 21. Citrus sudden death, oranges – Brazil (01 & 02). http://www.promedmail.org
Fundecitrus – Fund for citrus plant protection (Brazil). Morte Súbita dos citros. http://www.fundecitrus.com.br/msubita.html
Partnerships are the way to speed up solutions. http://www.fundecitrus.com.br/editorus.html