Enhancing Sorghum Yield Through Efficient Use of Nitrogen - Challenges and Opportunities

Abstract

Sorghum is an important crop, which is widely used as food, forage, fodder and biofuel. Despite its natural adaption to resource-poor and stressful environments, increasing yield potential of sorghum under more favorable conditions holds promise. Nitrogen is the most important nutrient for crops, having a dynamic impact on all growth, yield, and grain-quality-determining processes. Thus, increasing nitrogen use efficiency (NUE) in sorghum would provide opportunities to achieve higher yield and better-quality grain. NUE is a complex trait, which is regulated by several genes. Hence, exploring genetic diversity for NUE can help to develop molecular markers associated with NUE, which can be utilized to develop high NUE sorghum genotypes with greater yield potential. Research on improving NUE in sorghum suggests that, under water-deficit conditions, traits such as stay-green and altered canopy architecture, and under favorable conditions, traits such as an optimized stay-green and senescence ratio and efficient N translocation to grain, are potential breeding targets to develop high NUE sorghum genotypes. Hence, under a wide range of environments, sorghum breeding programs will need to reconsider strategies and develop breeding programs based on environment-specific trait(s) for better adaptation and improvement in productivity and grain quality. Unprecedented progress in sensor-based technology and artificial intelligence in high-throughput phenotyping has provided new horizons to explore complex traits in situ, such as NUE. A better understanding of the genetics and molecular pathways involving NUE, accompanied by targeted high-throughput sensor-based indices, is critical for identifying lines or developing management practices to enhance NUE in sorghum.

Keywords: grain quality; high-throughput phenotyping; sensors; source-sink relationships; stay-green.

FIGURE 1

Grain yield and protein (dry weight basis) at different N levels (A) and a visual comparison of confocal laser scanning micrographs of dried grain endosperm (green color obtained using fast green dye indicates protein) with differing grain protein content respective to the total N levels [(B) 87 kg ha⁻¹, (C) 201 kg ha⁻¹, and (D) 265 kg ha⁻¹]. Black vertical bars overlaying the gray bars (A) represent standard error (n = 4).

FIGURE 2

Visual comparison of plant greenness of maize (A; Photo credit to Rachel Veenstra), grain sorghum (B), and winter wheat (C) after physiological maturity and close to harvest maturity. Each image was captured when the respective crop was ready for mechanical harvesting.

FIGURE 3

Illustration comparing sorghum hybrids with increased terminal senescence under favorable environmental conditions with greater N translocation from leaves to increase yield and grain quality (left) versus stay-green sorghum hybrids grown under resource-poor conditions (right). Sorghum hybrids with efficient translocation of N and increased senescence under less stressful environments would potentially not require an extensive root system (left).