BUD FAILURE ON SWINGLE CITRUMELO IN A FLORIDA CITRUS NURSERY CAUSED BY XANTHOMONAS AXONOPODIS PV. CITRUMELO

GRAHAM, J. H.

Abstract


In 1997-1998, chronic failure of buds on Swingle citrumelo (Citrus paradisi × Poncirus trifoliata) rootstock in a field nursery was associated with foliar symptoms of citrus bacterial spot (CBS) caused by Xanthomonas axonopodis pv. citrumelo (Xac). Isolations from necrotic areas in the cambium of the rootstock under the bud yielded 15 isolates of bacteria. Bacteria were presumptively identified by fatty acid profile analysis as 10 different species including one isolate of Xac. These 15 isolates, another isolate of Xac from leaf lesions on affected Swingle citrumelo seedlings and 2 Xac isolates from CBS in previous nursery outbreaks were inoculated into the budunion of greenhouse-grown Swingle citrumelo during the budding process. After 17 days, all 4 isolates of Xac and one isolate of Pseudomonas putida caused severe necrosis and failure of Valencia orange buds on Swingle citrumelo. Twelve other isolates of bacteria from the budunion did not cause bud necrosis compared to the non-inoculated control. Bacteria that caused the greatest necrosis were the most difficult to recover after inoculation, whereas the bacteria that caused the least necrosis were the most easily recovered from the budunion. Treatment of the rootstock or bud before or after Xac inoculation with combinations of a fungicide and surface disinfectant failed to control necrosis and possibly suppressed microflora antagonistic to Xac. Nursery practices that limit survival of Xac on the rootstock should reduce infection of the budunion and consequent bud failure. These practices include: avoidance of overhead irrigation, increasing air movement to promote rapid drying of foliage, and performance of budding activities only under dry conditions.

Keywords


citrus paradisi × poncirus trifoliata; citrus bacterial spot; nursery irrigation practices; chemical control measures; surface disinfection

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Proc. Fla. State Hort. Soc.     ISSN 0886-7283