Tolerance to low temperatures and tuber soft rot in hybrids between Solanum commersonii and Solanum tuberosum obtained through manipulation of ploidyand endosperm balance number (EBN)

The objectives of this study were to evaluate the tolerance to low temperat ures and tuber soft rot in hybrids between Solanum commersonii and Solanum tuberosum. The experimental materials consisted of F-1 triploid, BC1 pentap loid-near pentaploid and BC2 tetraploid-near tetraploid hybrids. The F-1 tr iploids had a freezing tolerance and acclimatization capacity closest to S. commersonii. This indicated that the endosperm barriers which prevent the introgression of 1EBN S. commersonii into 4EBN S. tuberosum had been overco me. Indeed, the triploids produced 2n eggs, thus giving a compatible matern al to paternal EBN ratio in the hybrid endosperm generated by the 3x(2EBN) x 4x(4EBN) crosses. The tolerance to low temperatures of BC1 and BC2 hybrid s was lower than that of the F-1. However, a number of genotypes were ident ified which were able to withstand temperatures down to -5 degrees C. Some BC2 hybrids were also tested for their tolerance to tuber soft rot, and som e resistant hybrids were detected. A number of them combined the capacity f or cold acclimatization with tolerance to tuber soft rot. These hybrids hav e an EBN of 4; they are fertile and have been used in backcrosses with 4EBN S. tuberosum.