We found that BMV mutants carrying HVRs/HVRs and HVRs/HVRas sequences are as infectious as Mat0-BMV; usually they developed 14-18 lesions on each inoculated leaf. The two others, MatH-X-and MatNH-X-BMV mutants, are visibly less infectious and developed 3-5 and 4-8 lesions/leaf, respectively. Despite differences in their infectivity, BMV mutants carrying 3 0 HVRs and 5 0 HVRas as well as 3 0 Xs and 5 0 Xas supported non-homologous, heteroduplex-mediated crossovers very efficiently. An RNA3 recombinant was generated in 100 and 90% of lesions developed during infection with MatNH-HVR-and MatNH-X-BMV, respectively. Recombinant junction sites were located within the left portion of the local double-stranded region that could potentially be formed either by HVRs and HVRas or by Xs and Xas. As a result, both sequences supporting non-homologous crossovers were almost entirely deleted, together with the whole spacer ( Figure 5D and E) .