During evolution it is very common to find plant species that evolved from cross-pollination (when pollen is transferred from the anther of one flower to the stigma of another flower on a different plant) to self-fertilization (when a flower’s own pollen fertilizes its ovules or the ones from a different flower in the same plant). To study this evolutionary process, researchers have been mainly focused on animal-pollinated plants, and wind-pollinated species remain relatively understudied in this aspect. Now, a new study published in AoB PLANTS found that some floral traits play a key role in determining whether two closely related rice species, rely on selfing or outcrossing (wind-pollination).
Oryza rufipogon, a wild rice species has cross-pollination, while its sister species, Oryza nivara, has evolved toward a high rate of self-fertilization. This difference makes them an ideal couple for investigating the floral traits that drive different mating strategies in plants. By comparing their floral biology, researchers Michael Grillo and Andrés Gutiérrez identified key traits that differ between the two rice species, including anther and stigma characters, panicle shape, pollen viability, and the timing of anther opening to release pollen (dehiscence).
Two traits in O. nivara caught the authors’ particular attention: a larger anther basal pore size and an earlier anther dehiscence. These characteristics seem to ensure that pollen is released in a way that facilitates self-pollination, reducing the need for external pollen.
There is no difference in apical pore size between these species. However, there is a considerable difference in basal pore size, with O. nivara having a basal pore twice that of O. rufipogon.
To further investigate the mechanisms of selfing, researchers carried out floret manipulation experiments to differentiate between geitonogamy (selfing between different flowers on the same plant) and autogamy (selfing within a single flower). Their findings suggest that O. nivara relies mainly on autogamy, while O. rufipogon achieves selfing through geitonogamy.
Understanding these floral mechanisms is crucial not only for evolutionary biology but also for agriculture. Many staple crops, including rice, are wind-pollinated grasses. The findings of this study could help breeding strategies oriented at optimizing self-fertilization or maintaining genetic diversity in cultivated varieties.
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Grillo M. and Gutiérrez A. (2025) “Floral traits underlying mating system differentiation in the wind-pollinated sister species Oryza rufipogon and Oryza nivara” AoB PLANTS. Available at: https://doi.org/10.1093/aobpla/plae073
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