R. C. Cabunagan, International Rice Research Institute, Los Baños, Philippines
Bui Xuan Phong, Le Cuoc Cuong, Ho Van Chien and Nguyen Huu Huan, Ministry of Agriculture and Rural Development, Vietnam
In the summer-autumn crop season this year, farmers in Bac Giang province in Northern Vietnam observed yellowing symptoms in their rice crops about a month after high populations of green leafhoppers (GLH) were observed (Figure 1). The syndrome seemed similar to rice tungro virus disease, which is prevalent in Southeast Asia, However, scientists from Hanoi Agricultural University and Plant Protection Research Institute using RT-PCR identified the disease to be caused by the rice transitory yellowing virus (RTYV). The virus is known to be transmitted by GLH. RTYV (also known as rice yellow stunt virus) was first found in 1965 in Taiwan and in Southern and Central China, and later reported in Japan and Thailand. In 1985 the diseases were also reported in Vietnam and Laos.
Rice plants infected with RTYV show leaf yellowing, reduced tillering and mild stunting. Later, infected plants develop normal looking leaves and may appear healthy (thus, the name “transitory”) but symptoms may reappear after the temporary recovery. The virus is transmitted in a persistent manner by Nephotettix cincticeps, N. nigropictus and N. virescens. The virus propagates in the vectors, but it is not transmitted via eggs.
Leaf samples collected in Bac Giang province in September 2010 reacted positive to antiserum for RTYV by enzyme-linked immunosorbent assay, but they were negative for any of rice tungro spherical virus, rice tungro bacilliform virus, rice ragged stunt virus, and rice grassy stunt virus.