Unravelling root system architecture plasticity in response to abiotic stresses in maize

Abstract

Maize (Zea mays L.) production is often limited by edaphic stresses, viz., drought, salinity and nutrient deficiencies. The root system architecture (RSA) in is essential for efficient water and nutrient acquisition and overall plant stability under adverse conditions. Thus, identifying maize genotypes with desirable root characteristics under stress is a valuable strategy for breeding maize with enhanced abiotic stress tolerance and improved resource-use efficiency. The hydroponics-based root phenotyping offers control over the root environment, reduced labour, and almost damage-free phenotyping over field-based phenotyping. Here, we have investigated the adaptive RSA plasticity of maize under drought, low nitrogen, salinity, and non-stress environments. The results revealed significant variability for all the RSA-associated and related traits. The salinity-stressed genotypes showed adaptive plasticity with enhanced average root diameter (AD), whereas the enhanced total root length (TRL) and surface area (SA) were reduced along with average root diameter under low-N stress. The RSA traits TRL (total root length), SA (surface area), RV (root volume), SFW (shoot fresh weight), SDW (shoot dry weight), RFW (root fresh weight) and RDW (root dry weight) showed positive and significant correlations across the stress conditions (0.47 to 0.99; p < 0.001 to 0.05). Conversely, AD showed significantly negative correlations with SRL (-0.70 to -0.95; p < 0.001) of genotypes, stress (environment) and genotypes × stress (environment) interactions suggested the possibility of developing stress-specific maize cultivars by selecting inbred lines with high adaptive plasticity to specific stress environments or broad adaptability by selecting lines with high stability across stress environments. The results suggested that the maize RSA adapts not only specific root types and traits to cope with various environmental stress conditions but also the strength and directions of trait association. Notably, inbreds SKV671 and CML597 exhibited superior performance for various RSA traits under drought and low nitrogen conditions, while PML93 and MG42 excelled in salinity stress.

Keywords: Drought; Low-nitrogen; Maize; Plasticity; Root system; Salinity.

Fig. 1

Heatmap depicting the response of maize RSA and associated traits in response to control, drought, low-nitrogen and salinity environments under hydroponic conditions. The colour code from darker blue to darker red represents the lower to higher values for target traits.

Fig. 2

The box plots depict the descriptive statistics of RSA-associated and related traits. The red, sea serpent blue, green, and Chinese blue boxplots represent the control, drought, low-nitrogen and salinity stress environments. (A), Total root length (cm). (B), Surface area (cm². (C), Average diameter (mm). (D), Root volume (cm³. (E), Total number of roots (N). (F), Root length (cm). (G), Shoot length (cm). (H), Shoot fresh weight (g). (I), Root fresh weight (g). (J), Shoot dry weight (g). (K), Root dry weight (g). (L), SPAD value after stress. (M), Specific root length. (N), Root length distribution. (O), SPAD-value before stress.

Fig. 3

The dendrogram and PCA plot show the grouping of maize genotypes for RSA-related traits. (A), The dendrogram shows the clustering of diverse maize inbred lines for the RSA-related and associated traits mean values. The genotypes in red and blue colour indicates the exotic and indigenous inbred lines, respectively. (B), The PCA plot shows the distribution of genotypes for RSA-associated traits in maize. The X-axis represents the first principal component (PC1) and the Y-axis represents the second principal component (PC2).

Fig. 4

AMMI genotype × stress (environment) interaction biplots for RSA-associated traits. (A), Total root length (cm). (B), Surface area (cm². (C), Average diameter (mm). (D), Root volume (cm³. (E), Total number of roots (N). (F), Root length (cm). In each AMMI biplots, X-axis represents the first principal component (PC1) and the Y-axis represents the second principal component (PC2).

Fig. 5

AMMI genotype × stress (environment) interaction biplots for RSA-associated traits. (A), Shoot length (cm). (B), Shoot fresh weight (g). (C), Shoot fresh weight (g). (D), Root fresh weight (g). (E), Root dry weight (g). (F), SPAD value after stress. In each AMMI biplots, X-axis represents the first principal component (PC1) and the Y-axis represents the second principal component (PC2).

Fig. 6

AMMI genotype × stress (environment) interaction biplots for RSA-associated traits. (A), Specific root length. (B) Root length distribution. In each AMMI biplots, X-axis represents the first principal component (PC1) and the Y-axis represents the second principal component (PC2).

Fig. 7

GGE-which-won-where biplots for RSA-associated traits plasticity. (A), Total root length (cm). (B), Surface area (cm². (C), Average diameter (mm). (D), Root volume (cm³. (E), Total number of roots (N). (F), Root length (cm). In each GGE biplots, X-axis represents the first principal component (PC1) and the Y-axis represents the second principal component (PC2). The genotypes are represented by blue solid circle, while environments are indicated by solid green diamond shapes.

Fig. 8

GGE-which-won-where biplots for RSA-associated traits plasticity. (A) Root fresh weight (g), (B) Root dry weight (g), (C) Specific root length, (D) Root length distribution, (E) Shoot fresh weight (g). (F) Shoot dry weight (g). In each GGE biplots, X-axis represents the first principal component (PC1) and the Y-axis represents the second principal component (PC2). The genotypes are represented by blue solid circle, while environments are indicated by solid green diamond shapes.

Fig. 9

GGE-which-won-where biplots for RSA-associated traits plasticity. (A), Shoot length (cm). (B), SPAD value after stress. In each GGE biplots, X-axis represents the first principal component (PC1) and the Y-axis represents the second principal component (PC2). The genotypes are represented by blue solid circle, while environments are indicated by solid green diamond shapes.