Genotypic difference in the plasticity of root system architecture of field-grown maize in response to plant density

Abstract

To investigate genotypic differences in the plasticity of root system architecture in response to increasing planting density and understand how this plastic response affects grain yield. A two-year field study was conducted with eight maize hybrids and three planting densities (60,000, 75,000, and 90,000 plants per ha). High-throughput imaging system and an automatic analysis method with Root Estimator for Shovelomics Traits (REST) software were adopted to study root architecture. The coefficient of variation (CV) was determined to reflect the plastic response of the root traits at different planting densities. Root size and root architecture varied with increasing plant density and among the genotypes. With increasing planting density, root biomass and root length per plant decreased. The average root opening angle in inter-row and intra-row directions (RA), average root maximal width in inter-row direction and intra-row directions (RMW), ratio of root opening angle between intra-row and inter-row directions (RatioRA), and ratio of root maximal width between intra-row and inter-row directions (RatioRMW) were also reduced. These results suggest that plants growing under high planting density have narrower root extension width, steeper root angle, and greater root distribution in inter-row direction. The CV of all the root traits between the neighboring plants increased with increasing plant density. Although significant genotype × planting density interactions occurred with most of the root traits, there was a quadratic correlation between grain yield and most of the root traits, especially at high planting density (R2 = 0.17 ~ 0.48). There was a negative linear relationship between grain yield and the CV of root biomass, root length, RA, RMW, RatioRA, and RatioRMW (R2 = 0.21 ~ 0.37). Among the eight hybrids, JQ202 had medium root size, more inter-row root distribution, and the smallest CV in root traits across three planting densities, and the highest grain yield. LY99, SR999 and DY39 had largest CV for root traits and the smallest grain yield. Genotypes with less variation in root size, medium root size, medium broad root system and more inter-row root distribution help to reduce root-to-root competition and tend to have higher yield at high planting density.