To examine the role of the two 163-nt repeats in the recombination and/or selection, we deleted each repeat independently in C1C2 T2B T3. The resultant deletion mutants were designated C1C2 T2B T3 Á163(A) and C1C2 T2B T3 Á163(G) (Figure 1) , where the subscripts Á163(A) and Á163(G) represent the first 163-nt repeat deletion and the second 163-nt repeat deletion, respectively. Bioassay of C1C2 T2B T3 Á163(A) and C1C2 T2B T3 Á163(G) onto N. glutinosa plants showed that both deletion mutants induced similar symptoms to those induced by C1C2 T2B T3 (data not shown). Northern blot hybridization analysis showed that neither deletion affected the presence of recombinant RNA 3s in the multiple passage plants (Figure 2A, lanes 8 and 19 , data not shown). However, both deletion mutants yielded recombinant RNA 3s in both the inoculated plants and the passage plants (Figure 2A and B, compare lanes 4 and 15, and lanes 8 and 19, data not shown). Repeated inoculation and northern blot hybridization analysis gave the same results as earlier. This suggests that the two 163-nt repeats affected the rate of the recombination and/or selection of recombinants.