First Report of Citrus Blight in Costa Rica

Citrus blight (CB), causing a chronic decline of citrus, has been an important disease in Florida for over 100 years. CB was first reported in Brazil in the 1980s and is now responsible for the removal of nearly 10% of the trees from production annually. No causal agent has been identified, but CB has been root-graft transmitted to healthy trees, suggesting that the causal agent is infectious (3). Since 1997, CB symptoms were observed in several groves in northern Costa Rica, the most important citrus area of approximately 25,000 ha. Symptoms observed include a general decline and wilt of the tree canopy, off-color leaves, leaf drop, twig dieback, small fruit, delayed blossom, poor growth, and death. A survey near Guanacaste revealed CB symptoms in 7-yr-old Valencia and Pineapple orange trees (Citrus sinensis (L.) Osbeck) grafted on Carrizo citrange (C. sinensis (L.) Osbeck × Poncirus trifoliata (L.) Raf.) rootstock. Since 1997, 6% of the trees in this area have been replanted annually because of CB symptoms. Similar situations were observed in other groves in the northern citrus area. Dot immunobinding assays (DIBA) (1) were used to detect the P12 protein associated with CB with 20 of 22 trees showing CB-like symptoms giving a positive test. Zinc (Zn) accumulation in trunk wood and water uptake tests were done according to Roistacher (2) in 8 healthy and 20 symptomatic trees which were positive for CB using DIBA. The average Zn concentration of 16 declining trees was 4.6 ± 1.9, whereas the average concentration for 8 healthy trees was 2.0 ± 0.9. The average water uptake in 1 min was 14 ml for healthy trees, and virtually zero for the 20 symptomatic trees. These diagnostic tests confirm the presence of CB in the northern citrus area of Costa Rica, and the surveys indicate the disease is beginning to spread and become economically important. To our knowledge, this is the first report of CB in commercial citrus in Costa Rica. References: (1) K. S. Derrick et al. Plant Dis. 74:168, 1990. (2) C. N. Roistacher. Pages 57-66 in: Graft-Transmissible Diseases of Citrus. Handbook for Detection and Diagnosis. C.N. Roistacher, ed. Food and Agriculture Organization, Rome, 1991. (3) D. P. H. Tucker et al. Plant Dis. 68:979, 1984.