Abstract:
Xanthomonas oryzae pv. oryzae (Xoo), the causal organism of bacterial leaf blight (BLB), is one of the
most important pathogens in rice. Bacterial leaf blight disease develop yellowing symptoms in leaves reducing
the effective area for photosynthesis and eventually kills the plant. Therefore, precise assessment of disease
progression may help to manage the disease at early stages. This study was an attempt to develop a simple
smart phone method for assessing bacterial leaf blight in rice varieties in open fields. Two treatments of
inoculated and non inoculated with Xoo were applied over eight rice varieties (3 ½ month varieties: Bg 352,
Bg 358, Bg 360, Bg 366, and 4 month varieties: At 401, Bg 403, Bg 406 and Bg 407H) and the leaf reflectance
of red (R), green (G) and blue (B) were captured using a smart phone by inserting the leaf into an image
module box in order to create consistent environment conditions. As a ground truth data, the chlorophyll
change induced by the Xoo of the same leaf was measured using a SPAD meter during the trial. The
relationship between the image derived indices and measured chlorophyll content was investigated. Results
revealed that image derived R, G, B indices such as R, (R-G)/(R+G), (R-G)/(R+G+B), (R-B)/(R+G+B) strongly
correlated (83 % < R2 > 96%) with Xoo induced chlorophyll changes. It also suggested that there were
genetically influenced diversity in the pattern of each variety responded to the pathogen Xoo during BLB
progression. Therefore, the findings are encouraging to adopt advanced smart phone based technology for
quantitative assessment of diseases in future rice farming.
