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United States Department of Agriculture

Agricultural Research Service

Research Project: PECAN CULTIVATION AND DISEASE MANAGEMENT

Location: Fruit and Nut Research

Title: The activity of citrus canker lseions on grapefruit in Florida, June 2009-January 2010

Authors
item BOCK, CLIVE
item Parker, Paul -
item GOTTWALD, TIMOTHY
item Graham, Jim -

Submitted to: Phytopathology
Publication Type: Abstract Only
Publication Acceptance Date: May 6, 2010
Publication Date: June 1, 2010
Citation: Bock, C.H., Parker, P.E., Gottwald, T.R., Graham, J.H. 2010. The activity of citrus canker lesions on grapefruit in Florida, June 2009-January 2010 [abstract]. Phytopathology. 100:S15.

Interpretive Summary: Citrus canker causes severe damage to citrus in Florida. The lesions of the disease on citrus fruit render the fruit unfit for sale to the fresh market, and it can only be juiced, which is less profitable. Knowledge of the lesion activity in orchard-grown grapefruit can help gauge risk associated with infected fruit entering fresh markets. The proportion of active lesions, and the numbers of canker bacteria produced provide information that can be used in helping guide management and regulation of diseased fruit. Eighty lesions from the rind of grapefruit were collected monthly from June 2009 – January 2010 from an orchard in East Florida. There was a slight decline in the proportion of active lesions: in June 88% of lesions produced Xcc, and by January, at the time of harvest, 69% of lesions were active. However, the average number of bacteria produced remained fairly constant, and suggests that in Florida there was little change in the activity of canker lesions on fruit from shortly after lesion development to the point of harvest. This reinforces the need to focus on post harvest approaches to deactivating lesions of citrus canker on fresh fruit.

Technical Abstract: Lesions of citrus canker, caused by Xanthomonas citri subsp. citri (Xcc), on citrus fruit preclude sale of the fruit to the fresh market; the fruit must be juiced, which is less profitable. Assessing lesion activity in orchard-grown grapefruit provides information on the population dynamics of fruit lesions in a commercial situation that can help gauge risk associated with infected fruit entering fresh markets. To quantify the proportion of active lesions, and the numbers of Xcc bacteria produced, we collected eighty lesions from the rind of grapefruit on each of eight occasions (once a month from June 2009 – January 2010) from an orchard in East Florida and assessed activity of each lesion by dilution plating on nutrient agar. Linear regression analysis indicated a slight decline in the proportion of active lesions (R2 = 0.45). In June 88% of lesions produced Xcc, and by January, at the time of harvest, 69% of lesions were active. However, the average number of bacteria produced was greatest in November (3.9x105 Xcc/mm2 of lesion), and least in August (2.8x104 Xcc/mm2 of lesion). In January, 2.0x105 Xcc/mm2 lesion was produced. The maximum quantity of Xcc produced was in December (5.2x107 Xcc/mm2 of lesion). These data suggest that in Florida there was little change in the activity of canker lesions on fruit from shortly after lesion development to the point of harvest. Foliar lesions are also reported to remain fully active for at least six months. This reinforces the need to focus on post harvest approaches to deactivating lesions of citrus canker on fresh fruit.

Last Modified: 7/25/2014