Quantification of the Severity of Brown Leaf Spot Disease in Cassava using Image Analysis
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บทคัดย่อ
Accurate assessment of cassava brown leaf spot (BLS) disease severity is needed in epidemic monitoring and plant breeding. The objectives of this study were to develop an image analysis technique for quantifying infection levels of cassava BLS disease, and to compare the assessment results with conventional visual rating using Teri’s diagram key. Detached cassava leaves infected by BLS disease of contrasting severity were collected
from an experimental field. The leaf images were captured under controlled illumination. The images were preprocessed and read for primary RGB values. An image processing algorithm based on HSI color space has been developed for segmenting lesion region on a leaf using Otsu’s method which allows the counting of number of spots (N) and the calculation of percentage of infection area (PI). Manual scoring has been concurrently carried out by seven human raters using Teri’s illustrated diagram which orders BLS infection into 4 levels, representing lesion area of approximately 5, 10, 15 and 20% respectively. The Teri’s diagram itself was also scanned and presented to the image processing algorithm developed to investigate actual lesion area. Verification of Teri’s
diagram indicated that the Ns obtained from image analysis was 100% coincided with that counted by raters. On the other hand, the PI values obtained from image analysis were 0.87, 3.94, 9.87 and 18.71%, considerably smaller than visual approximation. Assessment of diseased leaf samples by image analysis and visual rating showed a good agreement for Ns (R2=0.8993), however, visual rating tended to overestimate the infection level
comparing with image analysis, and a large variation among raters could be observed. The results further suggested that the accuracy of spots detection vary proportionally with the infection level. This study has demonstrated the usefulness of image analysis in quantifying cassava BLS disease severity in that it provides more elaborate scaling and better consistency.
Article Details
สมาคมวิศวกรรมเกษตรแห่งประเทศไทย
Thai Socities of Agricultural Engineering
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