Relationship between polyploidy and pollen self-incompatibility phenotype in Petunia hybrida Vilm.

Self-incompatibility in Solanaceae is controlled by a single multiallelic locus, the S-locus. The S-allele associated ribonocleases (S-RNases) in the pistil are involved in pollen rejection. In this work, we analyzed two newly isolated lines of Petunia hybrida, termed PB and PF. They both had the same set of S-RNases (SB1- and S(B2-)RNases), however the PB was a self-incompatible diploid while PF was a self-compatible tetraploid. Cross pollination tests between PB and PF indicated diploid pollen from PF lost the incompatibility phenotype. In order to clarify the effects of polyploidy on pollen phenotypic change, we artifically induced tetraploid plants from a diploid (SSB2)-S-B1 heterozygote (=PB) and a diploid (SSB1)-S-B1 homozygote. The obtained S-B1 (SSSB1)-S-B1-S-B1 homoallelic tetraploid remained self-incompatible, whereas the (SSSSB2)-S-B1-S-B1-S-B2 heteroallelic tetraploid became self-compatible. These data suggested that the diploid heteroallelic pollen lost the incompatibility phenotype and had the characteristics of self-compatibility with (SSB2)-S-B1 style.