Evaluating Two Mass Screening Methods for Tungro Disease Resistance

Abstract

Tungro is one of the most destructive viral diseases of rice
in South and Southeast Asia. It is associated with two
viruses---rice tungro bacilliform virus (RTBV) ,and rice tungro
spherical virus (RTSV) (Hibino et al 1978). Both viruses are
transmitted by the green leafhopper (GLH) Nephotettix
virescens (Ling 1979), However, prior acquisition of RTSV is
required for Ihe transmission of RTBV alone (Hibino 1983).
Plants infected with both viruses show severe stunting and
yellowing. Those infected with RTBV alone show mild
stunting but no leaf discoloration whereas those infected
with RTSV alone do not show any apparent symptoms
(Hibino el al 1978).
Since the late 1960s, tungro has been mainly managed
through varietal resistance (Khush 1989). The instability of
resistant varieties in the field (Dahal et .a1 1990) led to a
reexamination of the nature of the incorporated sources of
resistance and to the adoption of more precise and more
accurate screening methods.