Enhancing maize yield through understanding the novel shoot-root interaction in morphology among hybrids with dense planting

Understanding the shoot-root characteristics and their interaction of maize is essential to break the constraints of the densification process and improve grain yield. The objective of the work was to study the interaction between the above-ground canopy and below-ground root system in morphology and its relationship to grain yield in dense planting with different hybrids. This study conducted a 2-yr field experiment with three modern hybrids (JNK728, ZD958 and XY335) at the Wuqiao Experimental Station in Northern China. Among hybrids, XY335 attained the highest grain yield of 14,886.9 kg hm−2 in 2019 and 10,078.8 kg hm−2 in 2020 with a density of 7.5 × 104 plants hm−2. For the shoot at the silking stage (R1), the lowest leaf orientation value for both middle and upper leaves and ear-to-height ratio among three hybrids were found in XY335 with the compact plant phenotype. Meanwhile, the highest photosynthesis rate of ear leaves (33.0 umol m2˙s−1) at R1 was also observed in XY335. At physiological maturity (R6), the above-ground dry matter (AGDM) was 4.6%− 10.4% higher in XY335 than the other two hybrids. For the root system at both R1 and R6 with the density of 7.5 × 104 plants hm−2, the highest value for root system indicators in morphology such as root total length (RL), root surface area (RSA), root volume (RV) was observed in XY335. From R1 to R6, RL, RSA and RV in XY335 averaged 24,749.6 cm, 3486.8 cm2, 51.5 cm3, 1.3–14.6% higher than JNK728, and 10.2–23.9% higher than ZD958, respectively. Furthermore, the lower senescence of the root system was also observed in XY335, with a 22.0–32.1% lower decrease from R1 to R6 in RL, RSA, and RV compared with the other two hybrids. For the shoot-root interaction, per unit decrease in morphology indicator in the root per plant with density increase of XY335 accompanied with more AGDM accumulation and thus higher grain yield. The observations on shoot-root characteristics and their interaction from this study are essential to selecting a hybrid that allows a better adaptation to planting at high density, developing an effective management strategy, and breeding high-density tolerant hybrids.