However, there are other explanations why DXho was absent in a large fraction of recombinants. It is possible that the mutation was removed either from MatH-RNA3, due to homologous recombination between its 3 0 RAS1 and wtRNA1, or from the RNA3 recombinant (carrying a single copy of RAS1) because it could also have recombined with wtRNA1. To examine the first possibility, progeny RNA3 extracted from the local lesions accumulating MatH-RNA3 (lesions in which recombinant was not generated) was analyzed. About 800 nt RT-PCR products obtained during selective amplification of RNA3's 3 0 -portion were cloned and sequenced. In all of 20 analyzed clones DXho was present. To test the second possibility, a full-length cDNA clone of RNA3 recombinant containing DXho (RNA3-DXhoR) was obtained. It was inserted into the pUC19 vector under the T7 polymerase promoter. The resultant plasmid named pRNA3-DXhoR was used after linearization to produce an infectious RNA3-DXhoR molecule by in vitro transcription. Then, RNA3-DXhoR was used together with wtRNA1 and wtRNA2 to inoculate C.quinoa plants. After 2 weeks, total RNA was extracted from individual lesions and a 3 0 -portion of the progeny RNA3 was amplified by RT-PCR. Obtained products were cloned and sequenced. As described previously, DXho was present in all of the analyzed 20 clones. These two experiments proved that homologous recombination between either 3 0 RAS1 of MatH-RNA3 or RAS1 present in RNA3 recombinant and wtRNA1 does not occur frequently enough to explain why most recombinants lack DXho. Altogether, these results supported our initial thesis that DXho was removed from 80% of homologous recombinants, since most of the crossovers occurred within 5 0 RAS1 from MatH-RNA3 and RAS1 from wtRNA1.