Casual agent of bacterial streak of rice

Xanthomonas oryzae pv. oryzicola is a gram-negative, rod-shaped bacterium.  It is emerging as an important pathogen of race (Oryza sativa) and is a recognized biosecuity threat to the United States.  Xoc enters through stomates or wounds, multiples in the mesophyll apoplast and causes bacterial leaf streak of rice.

Disease specifics

Xoc enters stomata, multiples in the substomatal chamber, and then progresses intercellularly in the mesophyll.  Leaf veins act as barriers as infected areas expand and coalesce, resulting in the leaf streak phenotype, i.e., thin, translucent lesions between the vascular bundles. At later stages infected leaves turn grayish white and die.  Exudates containing bacteria form small yellow filaments or beads on the surface of lesions.  These exudates are dislodged and carried easily by wind, rain splash, insects, and animals (including humans), resulting in spread of the disease.

Leaf streak can cause grain weight losses of up to 32%.  Though documentation is not yet available for many areas in which the disease is prevalent, available reports suggest that typical yield losses range from 0-17%, depending on the variety and climatic conditions.  The disease is increasing in importance in parts of Asia where modern hybrid rice varieties are grown, as these are particularly susceptible to the pathogen.  In some provinces of China, the disease is considered so important that is has been added to quarantine lists.  The disease is widely distributed in tropical and subtropical Asia, including China, Thailand, Malaysia, India, Vietnam, the Philippines, Indonesia, West Africa, South America, and Australia.