THE INTERNATIONAL JOURNAL OF
Self-incompatibility systems: barriers toself-fertilization in flowering plants
ANNE C. REA and JUNE B. NASRALLAH*
Department of Plant Biology, Cornell University, Ithaca, NY, USA
ABSTRACT Flowering plants (angiosperms) are the mostprevalent and evolutionarily advanced group of plants. Success of these plants is owed to several unique evolutionary adaptations that aid in reproduction: the flower, the closed carpel, doublefertilization, and the ultimate products of fertilization, seeds enclosed in the fruit. Angiosperms exhibit a vast array of reproductive strategies, including both asexual and sexual, the latter of which includesboth self-fertilization and cross-fertilization. Asexual reproduction and self-fertilization are important reproductive strategies in a variety of situations, such as when mates are scarce or whenthe environment remains relatively stable. However, reproductive strategies promoting cross-fertilization are critical to angiosperm success, since they contribute to the creation of genetically diversepopulations, which increase the probability that at least one individual in a population will survive given changing environmental conditions. The evolution of several physical and genetic barriersto self-fertilization or fertilization among closely related individuals is thus widespread in angiosperms. A major genetic barrier to self-fertilization is self-incompatibility (SI), which allowsfemale reproductive cells to discriminate between “self” and “non-self” pollen, and specifically reject self pollen. Evidence for the importance of SI in angiosperm evolution lies in the highly diverseset of mechanisms used by various angiosperm families for recognition of self pollen tube development and preventing self-fertilization.
KEY WORDS: plant reproductive barrier, pollination,...