Chapter 5

Abstract Gametophytic self-incompatibility (GSI), which prevents growth of a pollen tube through the style, provides a means of preventing self-pollination. Seen in most eudicot plant families, GSI in the genus Petunia was described by Darwin in the 19th century. By the time the first edition of this monograph was published in 1984, nearly a century later, most of the readily observable phenomena associ-ated with self-incompatibility in the genus Petunia had been described and, as in a number of other plant systems, it had been demonstrated to depend on the actions of genes encoded at a single highly polymorphic S-locus. Molecular research of the past two decades has provided a depth of understanding into the mechanisms under-lying the earlier observations, particularly in the identification of a number of SI-associated genes, their sites of action, and to some extent the mechanisms involved. This chapter summarizes what has been learned, with a focus on the molecular biology underlying GSI in Petunia, and highlights the major questions that remain unanswered. 5.1 Introduction....protected flowers with their own pollen placed on the stigma never yielded nearly