Citation: Ranjan, R.; Yadav, R.; Gaikwad, K.B.; Bainsla, N.K.; Kumar, M.; Babu, P.; Dharmateja, P. Spring Wheat’s Ability to Utilize Nitrogen More Effectively Is Influenced by Root Phene Variation. Plants 2023, 12, 1010. https://doi.org/10.3390/ plants12051010 Academic Editor: Oorbessy Gaju Received: 25 July 2022 Accepted: 19 September 2022 Published: 23 February 2023 Copyright: © 2023 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). plants Article Spring Wheat’s Ability to Utilize Nitrogen More Effectively Is Influenced by Root Phene Variation Rumesh Ranjan 1,2, * , Rajbir Yadav 1, *, Kiran B. Gaikwad 1 , Naresh Kumar Bainsla 1 , Manjeet Kumar 1 , Prashanth Babu 1 and Palaparthi Dharmateja 1 1 Division of Genetics, ICAR—Indian Agricultural Research Institute, New Delhi 110012, India 2 Department of Plant Breeding and Genetics, Punjab Agricultural University, Ludhiana 141004, India * Correspondence: rumeshranjan@pau.edu (R.R.); rajbiryadav@yahoo.com (R.Y.) Abstract: Genetic improvement for nitrogen use efficiency (NUE) can play a very crucial role in sus- tainable agriculture. Root traits have hardly been explored in major wheat breeding programs, more so in spring germplasm, largely because of the difficulty in their scoring. A total of 175 advanced/ improved Indian spring wheat genotypes were screened for root traits and nitrogen uptake and nitrogen utilization at varying nitrogen levels in hydroponic conditions to dissect the complex NUE trait into its component traits and to study the extent of variability that exists for those traits in Indian germplasm. Analysis of genetic variance showed a considerable amount of genetic variability for nitrogen uptake efficiency (NUpE), nitrogen utilization efficiency (NUtE), and most of the root and shoot traits. Improved spring wheat breeding lines were found to have very large variability for maximum root length (MRL) and root dry weights (RDW) with strong genetic advance. In contrast to high nitrogen (HN), a low nitrogen (LN) environment was more effective in differentiating wheat genotypes for NUE and its component traits. Shoot dry weight (SDW), RDW, MRL, and NUpE were found to have a strong association with NUE. Further study revealed the role of root surface area (RSA) and total root length (TRL) in RDW formation as well as in nitrogen uptake and therefore can be targeted for selection to further the genetic gain for grain yield under high input or sustainable agriculture under limited inputs. Keywords: genetic variation; root traits; nitrogen use efficiency; wheat; high N; low N 1. Introduction Wheat is consumed as a major dietary source of protein and carbohydrates by both humans and livestock [1] thus, the need to increase its production is undisputed. Globally, wheat occupies around 219 million ha of cropped area, which results in the production of around 760.9 million tons of wheat grains (FAOSTAT, 2020–2021). India is the second- largest producer of wheat grain (109.52 million tons, 2020–2021) after China, accounting for 14.3% of world wheat production. Increased nitrogen (N) fertilization besides dwarf and input responsive varieties were the major drivers of yield gain achieved during the second half of the 20th century [2] (Yadav et al., 2010). N is not only the most essential nutrient for higher grain yield realization but also a strong determinant for grain quality [3] (Marschner, 2012). Being a key element of protein, nucleotide, and chlorophyll, cereal crop plants use 20–50 g of N to produce a kilogram of biomass [4] (Robertson et al., 2009). N is the second most yield-limiting factor after soil water [5] (Campbell et al., 1993) and additional N applications are essential to optimize productivity and profitability. To carry out its essential functions, plants mostly absorb N from the soil and cannot use atmospheric N. Even among the available soil N, the plant can only absorb reactive N and soil does not carry enough reactive N (particularly nitrate and ammonia) to assist in plant development. Consequently, for crop production, farmers make use of water-soluble and readily absorbed chemical fertilizers. Global use of N fertilizer is continuously increasing and is estimated Plants 2023, 12, 1010. https://doi.org/10.3390/plants12051010 https://www.mdpi.com/journal/plants