DEVELOPMENT AND VALIDATION OF STANDARD AREA DIAGRAMS FOR ASSESSMENT OF COFFEE LEAF RUST (Hemileia vastatrix Berk. & Br.) SEVERITY IN COLOMBIA
Carlos Angel: National Coffee Research Center -Cenicafe
<div>Coffee Leaf Rust (CLR, <em>Hemileia vastatrix</em>) is one of the most devastating diseases for coffee worldwide, causing yield and quality losses between 23 and 50% in susceptible varieties without CLR management in Colombia. To support epidemiological, host resistance and management studies, two Standard Area Diagrams (SADs) to assess CLR severity on infected leaves from the field and from artificially inoculated plants were developed and validated. The SADs were composed of two sets of images with seven different percentages of affected leaf area (1, 2, 4, 8, 16, 32 and 64%), and validated by 10 non-expert and 10 expert raters based on their experience evaluating coffee diseases. Both groups estimated CLR first without any help; followed by two other CLR severity diagrams, and finally they used the new SADs. Lin's concordance correlation analysis of actual field CLR vs. estimated CLR using SADs showed 2.7 and 1.7% overestimation for non-experts and experts respectively, versus 24 and 7.6% when they did not use any diagram respectively. Interestingly, overestimation for artificially inoculated leaves were 1.59 and 5.24% respectively, and obtained similar values to the field CLR test when did not use any diagram. When the new SADs were used, 92.1% for field CLR and 50.5% for inoculated CLR of any possible rating combinations for raters in pairs were obtained within the highest frequency range of determinations (R<sup>2</sup> 0.9 to 1.0). The developed SADs for CLR severity visual assessment significantly improved reliability, accuracy and precision, for both experts and non-experts evaluators.</div>
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