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United States Department of Agriculture

Agricultural Research Service

Research Project: CHARACTERIZATION & EPIDEMIOLOGY OF CITRUS TRISTEZA VIRUS & OTHER INVASIVE & EMERGING GRAFT-TRANSMISSIBLE DISEASES OF CITRUS IN CALIFORNIA

Location: Crop Diseases, Pests and Genetics

Title: Effect of Citrus Stubborn Disease on Navel Orange Production in a Commercial Orchard in California

Authors
item Mello, Alexandre - OKLAHOMA ST.UV-STILLWATER
item Yokomi, Raymond
item Payton, Mark - OKLAHOMA ST.UV-STILLWATER
item Fletcher, Jacqueline - OKLAHOMA ST.UV-STILLWATER

Submitted to: Journal of Plant Pathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 18, 2009
Publication Date: October 1, 2010
Citation: Mello, A.F., Yokomi, R.K., Payton, M.E., Fletcher, J. 2010. Effect of Citrus Stubborn Disease on Navel Orange Production in a Commercial Orchard in California. Journal of Plant Pathology. 92:429-438.

Interpretive Summary: Citrus stubborn disease (CSD) is caused by Spiroplasma citri but the effect of the disease is not fully understood nor quantified. Therefore, the objective of this study was to determine the effect of CSD on tree size and production on navel orange trees naturally infected with S. citri in Central California. Results of this 2-year study indicated that fruit from infected trees were lighter, smaller, and more likely to be misshapen than those from healthy trees. Significant yield reduction occurred only in severely symptomatic trees where S. citri was broadly distributed within the tree canopy. All other variables such as canopy height, width, trunk diameter, and juice quality were statistically indistinguishable regardless of symptom severity or pathogen presence. However, the reduction in fruit yield and quality in severely infected trees validate the concern in California that CSD is a significant constraint to production and marketability of citrus.

Technical Abstract: The impact of citrus stubborn disease (CSD), caused by Spiroplasma citri, on citrus is not fully understood or quantified. The objective of this work was to measure the impact of S. citri infection on citrus production and assess bacterial distribution in trees differing in symptom severity. Infected and adjacent healthy navel orange trees were selected in a commercial grove in central California. Measurements included canopy height and width, trunk diameter, fruit number and the number of premature dropped fruit. Thirty fruit per tree were measured, weighed and evaluated for color, size and sunburn. Juice was extracted, weighed, and total soluble solids and titratable acidity were measured. Distribution of S. citri in trees with mild or severe symptoms was assessed by q-PCR and cultivation. Fruit from infected trees were lighter, smaller, and more likely to be misshapen than those from healthy trees. Significant yield reduction occurred only in severely symptomatic trees where S. citri was broadly distributed within the tree canopy. All other variables were statistically indistinguishable regardless of symptom severity or pathogen presence. The reduction in fruit yield and quality in severely infected trees validate the concern in California that CSD is a significant constraint to production and marketability.

Last Modified: 9/20/2014
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