Rice tungro disease (rice tungro virus)

Full symptoms occur if both rice tungro spherical virus (RTSV) and rice tungo bacilliform virus (RTBV) are present. RTSV enhances the tungro symptoms produced by RTBV. These symptoms vary in rice plants (Oryza sativa) of differing ages. Initial symptoms often begin with the yellowing of leaf tips, which then develop into yellow to orange discolouration of the leaves. In young plants, few tillers are produced and root development is incomplete. The plants, especially the younger ones, become stunted with small panicles and often unviable, deformed seeds. Localisation of the virus in vascular tissues reduces soluble sugars and causes an increase in the starch and amino acids in the plant (Azzam and Chancellor, 2002).

The disease is sometimes difficult to detect due to the variation in symptom expression, but it can result in losses of up to 74% (Ling, 1972). Brown, irregular blotches develop on leaves, and are more common on the younger plants. Leaves may also become mottled, or have light-green to white stripes parallel to the leaf veins (Hibino, 1996). If infection occurs at a young age, shortening of the leaf blade and leaf sheath result in the stunting of the plant. Root development is poor and flower development takes longer, which delays maturity and the panicles do not develop or exsert properly. Fewer grains are produced, and those that are yielded, have a reduced weight and may be coated in brown blotches (Suparyono et al., 2012).