Submitted to: Fruits
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/22/1997
Publication Date: N/A
Citation: Interpretive Summary: Citrus canker, a bacterial disease of citrus, has been a severe problem in many places in South America, Southeast Asia, and islands of the Indian Ocean archipelago. The disease seems to propagate and increase in citrus nurseries in response to rains and tropical storms. When nursery trees are transplanted to citrus plantations, the disease is moved to the plantations also. The large amounts of inoculum that move with nursery trees are detrimental to control of the disease in the plantations. In Reunion, a French Island off the east coast of Madagascar, different irrigation methods, including drip, mist, and overhead sprinkling, were investigated examined by starting a series of epidemics in nursery situations and monitoring disease progress and spread. It was found that drip and mist irrigation were favorable for the maintenance and control of low levels of citrus canker, which spread less under this management practice. Therefor citrus nursery production methods will be suggested for Reunion to reduce the amount of overhead watering in favor of other irrigation methods to decrease disease in nurseries and the introduction of disease to plantations.
Technical Abstract: In Reunion, control of citrus canker in nurseries, where infected plants are the main source of primary inoculum, can potentially improve disease control in new plantings. Because Xanthomonas axonopodis pv citri (Xac), associated with movement of infected nursery citrus, is a target of international phytosanitary quarantine, a sensitive and specific detection technique for Xac was developed allowing detection of approximately 10**2 cells per gram of citrus leaf. In most citrus growing areas in Reunion, year-round temperatures and annual rainfalls are conducive to infection by Xac. Spatial and spatio-temporal studies confirmed that disease patterns were aggregated in the field over time. Increase of disease rates was greatest in plots with overhead irrigation, whereas for plots with drip irrigation, the increase was less and associated with natural rainfall. To minimize citrus canker transmission to new groves, a modernization scheme for local citrus plant production was proposed. Grapefruit plants produced according to this improved scheme have been planted under various environmental conditions to experimentally determine the durability of citrus canker control resulting from the use of disease-free plants combined with other integrated control measures.