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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: Activity of citrus canker lesions on leaves, shoots and fruit of grapefruit in a Florida orchard from June 2010 to January 2011

Authors
item BOCK, CLIVE
item GOTTWALD, TIMOTHY
item Graham, Tim -

Submitted to: Phytopathology
Publication Type: Abstract Only
Publication Acceptance Date: May 6, 2011
Publication Date: June 1, 2011
Citation: Bock, C.H., Gottwald, T.R., Graham, T.H. 2011. Activity of citrus canker lesions on leaves, shoots and fruit of grapefruit in a Florida orchard from June 2010 to January 2011 [abstract]. Phytopathology. 101:S17.

Interpretive Summary: Lesions of citrus canker, caused by Xanthomonas citri subsp. citri (Xcc), on citrus fruit preclude export to certain markets. Characterizing the population dynamics of bacteria in canker lesions in commercial orchards can help gauge risk associated with diseased fruit entering fresh markets. The aim of this study was to quantify and compare lesion activity in citrus tissues up to harvest in an east central Florida grapefruit orchard. From June 2010 to January 2011 lesions on shoots, leaves and fruit were tested for activity. There was a decline in the proportion of active lesions for fruit from 98% to 6%, for leaves from 100% to 66% and for stems from 45% to 10%. Lesion activity was most erratic for stems. Although the greatest reduction in number of bacteria was with fruit lesions, considering lesions are active up to the point of harvest there is a role for postharvest disinfection treatments to mitigate Xcc on fresh fruit.

Technical Abstract: Lesions of citrus canker, caused by Xanthomonas citri subsp. citri (Xcc), on citrus fruit preclude export to certain markets. Characterizing the population dynamics of bacteria in canker lesions in commercial orchards can help gauge risk associated with diseased fruit entering fresh markets. The aim of this study was to quantify and compare lesion activity in citrus tissues up to harvest in an east central Florida grapefruit orchard. Each month from June 2010 to January 2011, twenty, fifty and eighty lesions were sampled from shoots, leaves and fruit, respectively. Lesion activity was quantified by dilution plating on nutrient agar and bioassay by injection infiltration into leaves of cv Duncan grapefruit. From June 2010 to January 2011, linear regression analysis indicated a decline in the proportion of active lesions for fruit from 98% to 6% (R2 = 0.80), for leaves from 100% to 66% (R2 = 0.44) and for stems from 45% to 10% (R2 = 0.41). Lesion activity was most erratic for stems. The maximum bacteria flux density (BFD, mm-2 min-1), a measure of inoculum production was 2.7 x 105, 2.4 x 105, and 1.4 x 104, bacteria mm-2 min-1 on fruit, leaves, and stems, respectively. Although the greatest reduction in BFD occurred for fruit lesions, considering lesions are active up to the point of harvest there is a role for postharvest disinfection treatments to mitigate Xcc on fresh fruit.

Last Modified: 9/29/2014
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