Genetic characterization of reduced melanin formation in tuber tissue of Solanum hjertingii and hybrids with cultivated diploids

The degree of enzymatic browning in tubers was examined quantitatively in f ive plant introduction (PI) accessions of Solanum hjertingii and in hybrids of this species with cultivated diploids that had high enzymatic browning. Polyphenol oxidase activity and melanin formation in S. hjertingii accessi ons was subjected to an analysis of variance, There was significant variati on in melanin formation within accessions but the between accession compone nt was not significant. This indicates that it would be most advantageous t o select low melanin formation by evaluating individual genotypes within an accession. Significant variation for PPO activity existed between accessio ns, indicating that selection on the basis of accession means would be the best means of selecting for lower PPO activity. Both parameters were much l ower in all S, hjertingii genotypes compared to tetraploid cultivars known for their susceptibility to internal blackspot when mechanically damaged, T he reduced browning ire S, hjertingii was due to a lack of PPO activity and not the shortage of substrate. Progenies, and parents of four crosses betw een selected S, hjertingii genotypes and cultivated diploids were measured for PPO activity and melanin formation. The mean performance of the progeni es was closest to the S, hjertingii parent in all cases. Degree of dominanc e indicated nearly complete dominance or overdominance in the direction of the S, hjertingii parent. These results are discussed in Light of other wor k which indicates that protein antigenic to PPO antibody is present in S, h jertingii. It appears that inactive PPO is present in the tubers. The prono unced dominance of low PPO activity and suppression of melanin formation in the hybrids with S. hjertingii is premising for the utility of this wild s pecies as a source of genetic factors that, upon introgression into the cul tivated potato gene pool, would suppress browning.