To confirm the role of the two 163-nt repeats in affecting the rate of recombination and/or selection, we generated two other deletion mutants, C1C2 W2B T3 Á163(A) and C1C2 W2B T3 Á163(G) . Bioassay of C1C2 W2B T3 Á163(A) and C1C2 W2B T3 Á163(G) showed that these two deletion mutants also induced symptoms similar to those induced by C1C2 W2B T3 (data not shown). Northern blot hybridization analysis showed that the deletions also resulted in the generation of the recombinant RNA 3s in both the inoculated and passage plants ( Figure 2C and D, compare lanes 26 and 33, and lanes 28 and 35, data not shown). These results showed that the two 163-nt repeats indeed affected the rate of the recombination and/or selection.