Citrus Sudden Death: A New Citrus Disease in Brazil

A new disease affecting sweet oranges on Rangpur lime rootstock, named Citrus Sudden Death, was first detected in the southwestern part of Minas Gerais and northern part of Sao Paulo states in 1999. Initially, affected trees present pale green leaves, followed by pro- nounced leaf drop, twig dieback, and occasional sucker growth of both scion and rootstock. Finally, trees quickly lose all their leaves and die about 6-mo after early symptoms appear. Young fruits remain attached to the twigs of dead trees. Cambial yellowing in the rootstock can be observed but there is no graft incompatibility, and symptoms are more pronounced during the spring. Symptoms have only been found on trees 6-yr or older. The roots have fewer feeder roots, and root rot occurs. The cause of this disease is unknown. Neither fungi nor nematodes appear to be causal agents. Citrus tristeza virus does not seem to be the cause either, and associations with nutrient disorders are not completely understood. The spatial evolution suggests the existence of foci and airborne transmission. Graft transmission trials have been initiated.