International Rice Research Institute, Los Baños, Philippines

Asystem for agroinoculating rice tungro bacilliform virus "RTBV#\ one of the two viruses of the rice tungro disease complex\ has been optimised[ A nontumour!inducing strain of A`robacterium "pGV2749# was used in order to conform with biosafety regulations[ Fourteen!day!old seedlings survived the mechanical damage of the tech! nique and were still young enough to support virus rep! lication[ The level of the bacterial inoculum was important to obtain maximum infection\ with a high inoculum level "9[4 0901 cells:ml# resulting in up to 099) infection of a susceptible variety that was com! parable with infection by insect transmission[ Agro! inoculation with RTBV was successful for all three rice cultivarss tested^ TN0 "tungro susceptible#\ Balimau Putih "tungro tolerant#\ and IR15 "RTSV and vector resistant#[ Agroinoculation enables resistance to RTBV to be distinguished from resistance to the leafhopper vec! tor of the virus\ and should prove useful in screening rice germplasm\ breeding materials\ and transgenic rice lines[