Development of A Smart Phone Method for Assessing Bacterial Leaf Blight (Xanthomonas oryzae pv. oryzae) in Rice Varieties

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.