The nature of the Bolivian weed potato species Solanum sucrense Hawkes

Summary Two theories for the origin of the Bolivian weed potato species Solanum sucrense Hawkes have been tested. The first was that it had an allopolyploid origin as a hybrid of the cultivated tetraploid S. tuberosum ssp. andigena (Juz. et Buk.) Hawkes with the wild/weed tetraploid cytotype of S. oplocense Hawkes. The second hypothesis postulated that it was a cross of the weed diploid species S. sparsipilum (Bitt.) Juz. et Buk. with S. oplocense.Synthetic hybrids of S. tuberosum ssp. andigena x S. oplocense and of S. sparsipilum x S. oplocense have been compared morphologically with S. sucrense accessions. Their crossability has also been investigated.The crossability and morphological studies strongly suggested that the former hypothesis was the more likely. This was borne out by observations made on the 1974 University of Birmingham Expedition when segregating populations of S. sucrense and S. oplocense were collected growing with feral S. tuberosum ssp. andigena.The evidence from this study indicates that the S. tuberosum ssp. andigena x S. oplocense hybrid has formed the basis of the S. sucrense gene pool. It is suggested that this hybridogenic taxon be maintained under the name Solanum x sucrense.The clarification of the taxonomic relationships of these three species will be of interest to Globodera resistance breeders, in view of the fact that these taxa are resistant to various pathotypes of the golden nematode.