One or more of the features that are needed to show you the maps functionality are not available in the web browser that you are using.
Please consider upgrading your browser to the latest version or installing a new browser.
More information about modern web browsers can be found at http://browsehappy.com/
Canker lesions begin as light yellow, raised, spongy eruptions on the surface of leaves, twigs and fruits. The lesions continuously enlarge from pin-point size over several months and can be of many different sizes based on the age of the lesion. As the lesions enlarge, the spongy eruptions begin to collapse, and brown depressions appear in their central portion, forming a crater-like appearance. The edges of the lesions remain raised above the surface of host tissue and the area around the raised portion of the lesion may have a greasy appearance. The lesions become surrounded by characteristic yellow halos. Canker lesions retain the erupted and spongy appearance under dry conditions, such as in a greenhouse; whereas they quickly enlarge and turn to flat lesions with a water-soaked appearance with frequent rain. Canker lesions vary in maximum size from 5 to 10 mm, depending on the susceptibility of the host plant. The symptoms are similar on leaves, fruit and stems.
Canker lesions are histologically characterized by the development of a large number of hypertrophic cells and a small number of hyperplastic cells. At an early stage of infection, the cells increase in size and the nuclei and nucleoids stain more easily; there is also an increase in the amount of cytoplasm synchronized with rapid enlargement. However, these hypertrophied cells do not divide; cell division is only detected in the peripheral areas of lesions adjacent to healthy tissue.
The lesions of canker B, C and D are similar in appearance and histology to those of canker A (Goto, 1992).
Reddy and Naidu (1986) reported canker lesions on roots; however, this has not been confirmed.
Safeguards for exporting citrus fruits into the USA from Japan include: the establishment of isolated canker-free export areas; inspection of fruit by plant pathologists in both countries during harvesting and packing operations; pre-shipping surface sterilization with bactericidal dip; pre-shipping inspection using the bacteriophage method to ensure fruits are free of X. citri; and certification by the Japanese Plant Protection Service that fruits are free of X. citri (Goto, 1992).
The disease has attracted widespread attention because of the serious efforts that have been made for eradication; these include destriction of citrus trees on a large scale and the implementation of strict international plant quarantine regulations against the pathogen (Stall and Civerolo, 1991; Goto, 1992).
The use of canker-free nursery plants is the first essential step in the management of citrus canker. Windbreaks established around citrus groves reduce disease. Pruning of angular shoots which hold canker lesions removes overseasoning inocula. Periodic spraying with insecticides to control the leaf miner, Phyllocnistis citrella, reduces infection sites (Goto, 1992).
Interactions between X. citri and antagonistic bacteria including Bacillus subtilis (Pabitra et al., 1996), Pantoea agglomerans (Goto et al., 1979), Pseudomonas syringae (Ohta, 1983) and P. fluorescens (Unnamalai and Gnanamanickam, 1984) have been reported in vitro and in vivo. However, the practical usefulness of these bacteria in controlling the pathogen has not been proved.
Due to the variable regulations around (de-)registration of pesticides, we are for the moment not including any specific chemical control recommendations. For further information, we recommend you visit the following resources:
Losses due to citrus canker primarily result from defoliation, premature fruit abscission and blemished fruit. It is not uncommon for almost 100% of the fruits and leaves of young, susceptible trees to be infected. Development and the achievement of full growth may be delayed in severely infected, young trees.
The impact of the disease has not been fully elucidated by the assessment of loss. The practical risk of transcontinental dissemination of citrus canker through lesions on marketable fruits requires investigation.