Characterizing Root Morphological Traits in 65 Genotypes of Foxtail Millet (Setaria italica L.) from Four Different Ecological Regions in China

Abstract

As an indispensable grain crop, foxtail millet (Setaria italica L.) is becoming a functional food in China because of its abundant nutrients. However, low rainfall and uneven precipitation limit its growth and production, especially in northwest China. Understanding the root phenotypic characteristics of foxtail millet is critical for utilizing its root characteristics to breed new millet varieties with improved resource-use efficiency and better adaptation to harsh environments. The present study characterized the variability of the root morphological traits at the seedling stage of 65 millet genotypes selected from four ecological regions across seven provinces in China. The plants were assessed after 21 days of growth in the germination pouches, and 48 root and shoot traits were measured. The results showed a large variation among the genotypes in the growth and functional traits. Among the measured traits, root dry mass, maximal root length, root surface area, and root tissue density contributed the most to the principal components. Root surface area ratio and root volume ratio were significantly correlated with root length ratio, respectively, while root length density and root weight density were negatively correlated with root diameter (p < 0.01). Shoot dry mass, root number, root length, root dry mass, and total dry mass were closely correlated with each other. Root length and root surface area in each 5-cm sections decreased from the top to the bottom along the root system. Among the four ecological regions, genotypes from the early maturing area of northwest China had the greatest root length, shoot dry mass, root dry mass, and root density, while those from the early maturing area of northwest China generally had the largest root system, with about 2.2 times more root length and dry weight than those from the early maturing area of northeast China (the shortest root system). The genotypic variability in root traits and correlations among shoot and root traits form a basis for breeding new millet cultivars.