Relationship Between Grain Yield Response Index and Wheat Genotypes Adapted to Nitrogen–Deficient Environments

Abstract Plant breeders of self-pollinated crops such as wheat often obtain huge number germplasms via hybridization programs. However, screening these germplasms to select the best ones, especially in terms of nitrogen (N) use efficiency, is not an easy task. Thus, the current study was designed to determine the significance of grain yield response index (GYRI) as a promising parameter versus the traditional agronomic traits to characterize the most efficient and responsive wheat genotypes to applied N. The study involved twenty bread wheat genotypes (six commercial varieties namely Sakha 94, Sakha 95, Giza 171, Gemmiza 12, Masr 1, Masr 2 and 14 new lines, numbered from 1 to 14). Over two seasons, the performances of these genotypes were monitored under three N levels: optimum N (192 kg N ha–1, farmer practice), moderate deficit N (144 kg N ha–1+biofertilizer) and high deficit N (96 kg N ha–1+biofertilizer). The experiment was designed in split-plot and replicated thrice. Line 11 under optimum N or high deficit N and Line 4 under moderate deficit N in the first season as well as Line 14 under high deficit N in the second season had the earliest heading time. Under normal N application (192 kg N ha–1), Masr 1 in the first season and Gemmiza 12 in the second season had the widest flag leaf. Under moderate deficit N, Line 6 in the first season and Line 14 in the second one surpassed all other genotypes. Application of 144 kg N ha–1+biofertilizer×Line 3 in the second season outperformed all other genotypes grown under the other N treatments. Line 9, Line 10, Line 13, Sakha 95 and Gemmiza 12 (under moderate deficit N) as well as Line 7, Line 8, Line 9, Line 13, Line 14, Gemmiza 12 and Masr 1 (under high deficit N) recorded the greatest values of grain yield in the first season. While, Sakha 95 and Line 9 were the marked genotypes for producing the maximum grain yield under moderate deficit N and high deficit N, respectively, in the second season. GYRI estimation exhibited that Line 11 and Sakha 95 in the first season and Sakha 95 and Masr 2 in the second one were the efficient and responsive genotypes for N applications. Obviously, GYRI as a breeding parameter can contribute greatly to resolving the conflict between crop traits in terms of distinguishing N-deficiency tolerant varieties. Herein, GYRI detected that Line 11, Sakha 95 and Masr 2 are considered promising germplasms to develop and improve wheat to tolerate low N supply. Further, the increased grain yield of some tested genotypes (i.e. Line 5, Line 6, Line 8, Line 9, Line 13, Line 14, Giza 171, Masr 1, Gemmiza 12) under deficit N than optimal N is an observation worthy of in-depth future investigation.