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

Self-incompatibility in Solanaceae is controlled by a single multiallelic l ocus, the S-locus. The S-allele associated ribonocleases (S-RNases) in the pistil are involved in pollen rejection. In this work, we analyzed two newl y isolated lines of Petunia hybrida, termed PB and PF. They both had the sa me set of S-RNases (SB1- and S(B2-)RNases), however the PB was a self-incom patible diploid while PF was a self-compatible tetraploid. Cross pollinatio n tests between PB and PF indicated diploid pollen from PF lost the incompa tibility 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 o btained S-B1 (SSSB1)-S-B1-S-B1 homoallelic tetraploid remained self-incompa tible, 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-com patibility with (SSB2)-S-B1 style.