RT-PCR detection of nonchimeric BSMV RNA sequences. Total RNA from individual healthy plants (lane 1), MStV- + BSMV-doubly infected plants (lane 2), BSMV-infected plants (lane 3), mixed RNAs from plants singly infected by MStV and BSMV (lane 4), and RNA from a MStV-infected plant (lane 5), was converted to cDNA using the BSMV primers BSMV7 (A, D), BSMV8 (B, E), or BSMV9 (C, F, see Table 1). The cDNA was amplified using the following PCR primer pairs: 5′BSMV1 and 3′BSMV4 (A), 5′BSMV2 and 3′BSMV5 (B), 5′BSMV3 and 3′BSMV6 (C), to detect BSMV RNAs α, β, and γ, respectively. Primers 5′MStV-CON and 3′BSMV4 (D), 5′MStV-CON and 3′BSMV5 (E), or 5′MStV-CON and 3′BSMV6 (F) were used in attempts to detect MStV/BSMV chimeric RNAs. One-tenth of the PCR reaction was electrophoretically separated in 3.5% Metaphore agarose followed by staining with ethidium bromide. Sizes of fragments were estimated by using the BRL 1-kb DNA ladder (not shown).