Nitrogen Use Efficiency in Sorghum: Exploring Native Variability for Traits Under Variable N-Regimes

Abstract

Exploring the natural genetic variability and its exploitation for improved Nitrogen Use Efficiency (NUE) in sorghum is one of the primary goals in the modern crop improvement programs. The integrated strategies include high-throughput phenotyping, next generation sequencing (NGS)-based genotyping technologies, and a priori selected candidate gene studies that help understand the detailed physiological and molecular mechanisms underpinning this complex trait. A set of sixty diverse sorghum genotypes was evaluated for different vegetative, reproductive, and yield traits related to NUE in the field (under three N regimes) for two seasons. Significant variations for different yield and related traits under 0 and 50% N confirmed the availability of native genetic variability in sorghum under low N regimes. Sorghum genotypes with distinct genetic background had interestingly similar NUE associated traits. The Genotyping-By-Sequencing based SNPs (>89 K) were used to study the population structure, and phylogenetic groupings identified three distinct groups. The information of grain N and stalk N content of the individuals covered on the phylogenetic groups indicated randomness in the distribution for adaptation under variable N regimes. This study identified promising sorghum genotypes with consistent performance under varying environments, with buffer capacity for yield under low N conditions. We also report better performing genotypes for varied production use—grain, stover, and dual-purpose sorghum having differential adaptation response to NUE traits. Expression profiling of NUE associated genes in shoot and root tissues of contrasting lines (PVK801 and HDW703) grown in varying N conditions revealed interesting outcomes. Root tissues of contrasting lines exhibited differential expression profiles for transporter genes [ammonium transporter (SbAMT), nitrate transporters (SbNRT)]; primary assimilatory (glutamine synthetase (SbGS), glutamate synthase (SbGOGAT[NADH], SbGOGAT[Fd]), assimilatory genes [nitrite reductase (SbNiR[NADH]3)]; and amino acid biosynthesis associated gene [glutamate dehydrogenase (SbGDH)]. Identification and expression profiling of contrasting sorghum genotypes in varying N dosages will provide new information to understand the response of NUE genes toward adaptation to the differential N regimes in sorghum. High NUE genotypes identified from this study could be potential candidates for in-depth molecular analysis and contribute toward the development of N efficient sorghum cultivars.

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

“…Responses of crops to nitrogen is mainly determined by their genetic background, and the complexity of NUE-related traits is controlled by multiple genes ( Bollam et al, 2021 ). Thus, exploring genetic diversity for key traits associated with NUE is a promising route to develop high-NUE sorghum hybrids.…”

“…Integration of these high-throughput phenotyping tools with advanced next generation sequencing-based genotyping would help to explore potential genetic variability for nitrogen utilization efficiency in sorghum. A native genetic variability in key yield traits related to NUE has been reported in a diverse set of sixty sorghum genotypes under low nitrogen regime ( Bollam et al, 2021 ). Thus, potential genetic variability for N uptake and utilization efficiency exists and can be exploited by evaluating larger sets of diverse genotypes with high-throughput phenotyping and genotyping tools.…”

“…Sorghum [ Sorghum bicolor (L.) Moench, Poaceae] is an important C 4 crop that is mainly utilized for human food, animal feed, forage, and fodder, but it is also an important source of fiber and feedstock for biofuel production ( Bollam et al, 2021 ). Sorghum is grown worldwide and distributed across different continents including North America, Africa, Asia, and Australia ( Kimber, 2000 ; Morris et al, 2013 ).…”

“…However, sorghum yields may increase substantially with an adequate supply of nutrients. For example, higher grain yields under intensive agricultural systems have been achieved with adequate nitrogen (N) supply ( Mahama et al, 2014 ; Bollam et al, 2021 ). Research on sorghum-yield improvement has been focused mainly on gaining smaller increments under marginal and unfavorable environments, and limited efforts have been invested in exploiting the true genetic potential of sorghum.…”

“…Exploring natural, genetic diversity for NUE is one of the potential strategies that can be used to enhance NUE in sorghum. This would involve integration of high-throughput phenotyping (HTP), next-generation-sequencing (NGS)-based genotyping technologies, -omics analysis, and identification of candidate gene(s) ( Masclaux-Daubresse et al, 2010 ; Bollam et al, 2021 ). However, physiological traits and molecular pathways that affect N uptake, assimilation, and remobilization in plants are complex ( Gastal and Lemaire, 2002 ), and they get further complicated when interactions of N metabolism with different environmental factors are considered ( Nasraoui et al, 2013 ; Das et al, 2017 ).…”