Long-term maize breeding reduced plant-to-plant yield variability, especially in water limited environments

Maize ( Zea mays L.) canopies of the same genotype are composed of plants that differ in their growth and yield. The yield variability of individual plants has commonly been proposed as a trait that explains genotype differences in their yield response to plant population and drought stress tolerance, responses that have changed with long-term breeding for yield. However, this has never been tested. Describe long-term breeding effects on plant-to-plant yield variability under different water availability environments. We analyzed the plant-to-plant yield variability of 71 commercial genotypes released from a continuous breeding program in the center US over the past century. These genotypes were grown under high plant populations (9.4–12.0 plants m −2 ) across 13 environments with different water availability. The coefficient of variation of yield per plant decreased from 80 % in genotypes commercialized in the 1930s to 17 % in those commercialized today (-0.74 % yr −1 , p < 0.001). This reduction in the plant-to-plant yield variability is explained by both, a reduction in the percentage of barren plants (p < 0.001) and an increased uniformity of the fertile plants (p < 0.001). Plant-to-plant yield variability was higher in double and triple-cross hybrids compared to single-cross ones. Still, single-cross hybrids also showed a similar reduction over time when analyzed separately (-0.67 % yr −1 , p < 0.001). Low-yielding drought stress environments (irrigation covering less than 70 % of evapotranspiration, or ET) showed canopies with larger plant-to-plant yield variability when compared to well-watered high-yielding ones (p < 0.001; irrigation covering above 90 % ET), and the genetic gain of canopy uniformity in yield was three times greater in low-yielding drought conditions compared to the high-yielding well-watered ones (-0.82 vs. −0.29 % y −1 , respectively). Modern genotypes can maintain significantly lower plant-to-plant yield variability than their older counterparts under drought stress. Findings support the concept that the increased plant population and drought tolerance of modern genotypes are associated with the ability to maintain canopies with low plant-to-plant yield variability. • Individual plant-to-plant yield variability was studied in maize genotypes released from 1920 to 2020. • Long-term breeding reduced the plant-to-plant yield variability under high plant populations. • Reduced plant-to-plant yield variability was driven by less barren plants and more uniform ears. • When only considering single-cross hybrids they also showed plant-to-plant yield variability reductions over time. • Yield variability among plants was particularly reduced in drought environments with low yields.