Response of pollen tube growth and seed set to controlled pollination and their relation to self-incompatibility in different cultivars of Petunia hybrida

Self-incompatibility is a widespread mechanism in flowering plants which prevents self-fertilisation and promotes out-crossing. In this investigation, self-compatible and self-incompatible cultivars of Petunia hybrida Vilm. were discriminated based on the study of pollen tube growth in vivo, seed set percent and index of self-incompatibility (ISI) after self- and cross-pollination. After 48 hours of self- and cross- pollination, the pollen tube growth was studied by aniline blue staining and fluorescent microscopy. Fluorescent microscopy studies showed normal germination and growth of pollen tubes on stigmas but some abnormalities of pollen tube growth were observed in self-pollinated styles in some cultivars. These abnormalities include pollen tube growth inhibition in 2/3 upper part of the style, variable pollen tube diameter in middle and lower part of the style and irregular deposition of callose plugs. ISI studies showed a significant decrease in the seed set of self-pollinated pistils compared with cross-pollinated pistils in some cultivars. The self-pollinated cultivars contain abnormalities in pollen tube growth after self-pollination as well as those with decreasing ISI was defined as self-incompatible in our study.