Submitted to: Conference of International Organization of Citrus Virologists
Publication Type: Proceedings
Publication Acceptance Date: 5/22/1997
Publication Date: N/A
Interpretive Summary: Numerous virus diseases affect citrus production worldwide, and in an era with intense international commerce and travel, there is a constant hazard that a disease present in a distant country can be imported and established in the U.S. When a vector for the disease is also present, the hazard of extensive natural spread increases. Recently, a new virus-like disease was observed in a major citrus growing area in Turkey. This disease, which has been named citrus chlorotic dwarf (CCD), causes stunting and severe crop loss in a number of citrus cultivars. CCD appeared following introduction of the Bayberry whitefly into Turkey and experiments have shown that the causal agent is vectored by this whitefly. The causal agent of CCD was probably present in another crop and has been spread into citrus. Since the Bayberry whitefly is already present in the U.S., this disease could pose a considerable future threat. Cooperative work with Turkish scientists has been initiated to characterize the causal agent, determine its long-term effects on citrus production, develop rapid diagnostic tests and clarify the epidemiology of this disease. The current paper describes observations on disease distribution in the field and transmission of the causal agent using a stem slash inoculation technique. In vitro assays such as this are essential for making further progress in identifying the causal agent.
Technical Abstract: A new virus-like disease of citrus was observed in the eastern Mediterranean region of Turkey at the end of the 1980s. Field symptoms consist of a V-shaped notch and chlorotic flecking on young leaves, and warping, crinkling, inverted cupping, and variegation on mature leaves. This disease has been named "Citrus Chlorotic Dwarf" (CCD). CCD has been observed on 12 citrus varieties including sweet orange, mandarin, grapefruit, and lemon. Sweet orange was the least affected. The highest disease incidence (49%) was found in the Icel area, whereas only a few diseased trees were observed in Adana or Hatay. In the laboratory, the pathogen was transmitted frequently by the Japanese bayberry whitefly, Parabemisia myricae (Kuwana). The transmission rate increased from 18% to 46% with an increase in the inoculation access period from 24 to 48 hr. The pathogen was transmitted to rough lemon by stem-slash inoculation at a rate of 5% (5 cuts) to 72% (100 cuts). The causal agent was not transmitted mechanically by leaf inoculation to citrus or herbaceous plants.