Disease Development and Discovery of Anatomically Resistant Features towards Bacterial Leaf Streak in Rice

Bacterial leaf streak (BLS) caused by bacterium Xanthomonas oryzae pv. oryzicola (Xoc) is one of the most prominent rice diseases. BLS causes a significant reduction in paddy yields. However, there are limited studies and a lack of information regarding the mechanisms and cells affected on leaf tissues severed from this disease. Therefore, in this study, sensitive paddy variety IR24 was inoculated against BLS, and the pathogen colonised mesophyll cells and some bundle sheath cells. The infection spreads rapidly towards the base and apex of the leaf, but rather slowly to the left and right sides of the leaf veins. Another experiment was performed to unravel anatomical characteristics in sensitive paddy varieties (TN1, IR24, IR5) and resistant paddy varieties (IR26, Dular, IR36) against BLS. Susceptible paddy varieties have less thick midrib and leaf lamina, a high number of bundle sheath cells at primary vascular tissue (midrib), one layer of sclerenchyma cells at the secondary vein, and more than two metaxylems at the primary vein. Resistant paddy varieties, on the other hand, consist of a relatively thickened midrib and leaf lamina, fewer bundle sheath cells at the primary vascular tissue (midrib), more than one sclerenchyma layers at the secondary vein, and two metaxylems at the primary vein. This study contributes new knowledge in identifying the level of infection in paddy fields, and helps breeders in producing resistant paddies to this disease.