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ARS Home » Southeast Area » Byron, Georgia » Fruit and Tree Nut Research » Research » Publications at this Location » Publication #302672
Title: Development and validation of standard area diagrams as assessment aids for estimating the severity of citrus canker on unripe oranges

Author
item BRAIDO, RICARDO - University Of Maringa
item GONCALVES-ZULIANI, ALINE - University Of Maringa
item JANEIRO, VANDERLEY - University Of Maringa
item CARVALHO, SERGIO - University Of Maringa
item BELASQUE, JUNIOR - Universidad De Sao Paulo
item Bock, Clive
item NUNES, WILLIAM - University Of Maringa

Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/28/2014
Publication Date: 11/1/2014
Citation: Braido, R., Goncalves-Zuliani, A.O., Janeiro, V., Carvalho, S.A., Belasque, J.J., Bock, C.H., Nunes, W.M. 2014. Development and validation of standard area diagrams as assessment aids for estimating the severity of citrus canker on unripe oranges. Plant Disease. 98:1543-1550.

Interpretive Summary: Citrus canker is an important disease in Brazil and elsewhere in the world where citrus is grown. The disease can cause yield loss and lead to imposition of trade barriers. The objective of this research was to construct and validate standard area diagram sets (SADs) as assessment aids for raters to improve the accuracy and reliability of visual estimates of citrus canker on unripe fruit of sweet orange. Two SADs were constructed. A 5-diagram SADs had five severities depicted (0.5, 2.0, 8.0, 27.0 and 40.0%) and a 6-diagram SADs had six severities depicted (0.5, 1.0, 3.0, 9.0, 20.0 and 40.0%). Raters with a range of experience of disease assessment and of familiarity with citrus canker symptoms evaluated the 40 images of cankered, unripe fruit. Both the 5- and 6-diagram SADs significantly improved the accuracy and reliability of estimates. The 5-diagram SAD set was slightly more accurate and reliable compared to the 6-diagram set. Possible reasons for this are discussed. Although the SAD set was developed for sweet orange, it doubtless has applicability to other citrus, including grapefruit. These SADs should be useful for research and disease management where accurate and reliable estimates of the severity of citrus canker are sought.

Technical Abstract: Canker is an important disease of citrus in Brazil and elsewhere in the world. Infection with the causal pathogen, Xanthomonas citri subsp. citri can cause severe disease on the fruit. In the course of research and disease management, the severity of citrus canker must often be estimated visually by raters. The objective of this research was to construct and validate standard area diagram sets (SADs) as assessment aids for raters to improve the accuracy and reliability of visual estimates of citrus canker on unripe fruit of sweet orange. Two SADs were constructed. A 5-diagram SADs had five severities depicted (0.5, 2.0, 8.0, 27.0 and 40.0%) and a 6-diagram SADs had six severities depicted (0.5, 1.0, 3.0, 9.0, 20.0 and 40.0%). Fifteen raters with a range of experience of disease assessment and of familiarity with citrus canker symptoms evaluated 40 images of cankered, unripe fruit. Both the 5- and 6-diagram SADs significantly improved the accuracy and reliability of estimates. Agreement, measured by Lin’s concordance correlation coefficient was 0.220 to 0.913 when not using SADs, 0.814 to 0.955 when using 5-diagram SADs, and 0.863 to 0.925 when using 6-diagram SADs. The 5-diagram SAD set was significantly more accurate and reliable compared to the 6-diagram set. Possible reasons for this are discussed. Based on the results, the 5-diagram SADs is preferable to use. Although the SAD was developed for sweet orange, it doubtless has applicability to other citrus, including grapefruit. These SADs should be useful for research and disease management where accurate and reliable estimates of the severity of citrus canker are sought.