Premature pollen development hinders autonomous self-pollination and promotes insect pollination in soybean (Glycine max L.)

Abstract

Flower traits (e.g., self-compatibility) determine pollinator dependence, and thereby seed production and mating. But crop research often overlooks how specific flower traits influence pollination quantity and quality and, consequently, yield. Our study addresses this oversight by investigating how the under-studied phenomenon of premature pollen development (PPD)—where pollen germinates inside the anther before dispersal—affects pollinator dependence in soybean, a globally important crop. Soybean exhibits both PPD and variable pollinator dependence. To link these two factors, we conducted a four-week study across 15 experimental plots within a 24-hectare soybean plantation in Central Argentina. We collected 186 flowers and pollinator visitation data to analyze how PPD and visitation frequency affected pollen tube growth in the style. Our findings indicate that PPD limits autonomous self-pollination while simultaneously increasing pollinator dependence. Interestingly, small wild pollinators appear to be more effective at pollen transfer than managed honeybees. This work highlights the potential consequences of PPD on soybean yield and suggests the critical role of wild pollinators when PPD is present. Our findings underscore the need to preserve pollinator habitats to maintain high productivity, even in seemingly self-pollinating crops. They also raise questions about the role and consequences of PPD in plant reproduction beyond agriculture.