Mitigating Constraints in Harvest Index and Yield of Densified Populations via Sink Modulation of Narrowing Pollination Time Gaps within Maize Ear

The densification of cereal crops increases population but simultaneously reduces the grain number per individual plant, constraining harvest index and overall yield. Since asynchronous pollination within spike/ear is conserved among cereals, its role in determining yield formation under densification remains unclear. Here, we varied pollination time gaps (PTG, defined as the duration required for all silks in an ear to emerge and be pollinated) to examine how PTG affects grain development and overall yield as planting density increases. Results showed that densification exacerbated PTG and increased grain abortion. Eliminating PTG through synchronous pollination (SP) recovered more than 20% of density-induced grain loss per ear and increased harvest index by 3.7∼3.9% and total yield by 4.9∼11.7%, along with higher optimal density. Using 13C-labeling to quantify daily carbon assimilates, SP increased carbon allocation to the ear and grains, while significantly decreasing carbon stored in vegetative tissues. Surprisingly, photosynthesis rates were also enhanced during the subsequent filling stage. These findings suggest a synergistic enhancement of sink and source capacities under densified populations with SP. Additionally, removing early pollinated grains at the grain set stage increased carbon availability to later-pollinated grains and prevented their abortion, confirming PTG's role in carbon allocation within the ear for determining grain number. Validated across different varieties and years, we propose PTG as a new trait for breeding and management to enhance harvest index and yield potential in densified populations. This sink modulation approach complements existing strategies focused on improving source capacity and may be applicable across various cereals with asynchronous flowering.