Abstract
Nitrogen (N) fertilizer represents a significant cost for the grower and may also have environmental impacts through nitrate leaching and N2O (a greenhouse gas) emissions associated with denitrification. The objectives of this study were to quantify the genetic variability in N-use efficiency (NUE) in Indian spring wheat cultivars and identify traits for improved NUE for application in breeding. Twenty eight bread wheat cultivars and two durum wheat cultivars were tested in field experiments in two years in Maharashtra, India. Detailed growth analysis was conducted at anthesis and harvest including dry matter (DM) and N partitioning. Senescence of the flag leaf was assessed from a visual score every 3–4 days from anthesis to complete flag-leaf senescence and fitted against thermal time to estimate the onset and end of post-anthesis senescence. Grain yield (GY) was reduced under low N (LN) by an average of 1.46 t ha−1 (−28%). Significant N × genotype level interaction was observed for grain yield and NUE. Above-ground N uptake at harvest was reduced from 162 kg N ha−1 under high N (HN) to 85 kg N ha−1 under low N (LN) conditions, while N-utilization efficiency (grain DM yield per unit crop N uptake at harvest; NUtE) increased from 32.7 to 44.6 kg DM kg−1 N. Genetic variation in GY under LN related mainly to variation in N uptake at harvest rather than NUtE; and the N × genotype effect for GY was mainly explained by the interaction for N uptake at harvest. Averaging across years, the linear regression of onset of flag-leaf senescence on GY amongst cultivars was significant under both HN (R2 0.16. p < 0.05) and LN (R2 0.21, p < 0.05) conditions. Onset of flag-leaf senescence was positively associated with N uptake at anthesis under HN (R2 0.34, p < 0.001) and LN (R2 0.22, p < 0.01) conditions. Flag-leaf senescence timing was not associated with post-anthesis N uptake. It is concluded that increased N accumulation at anthesis was correlated with flag-leaf senescence timing and that N accumulation at anthesis is an important trait for enhancing grain yield and NUE of wheat grown under low to moderate N supply in India.
Highlights
Wheat (Triticum aestivum L.) is the most widely grown cereal crop in the world, and accounts for 20% of the calories consumed by the global population (FAO, 2016)
Delayed senescence was only apparent at higher N supply; in the stay-green line 3, a greater N uptake was observed in the main tiller and the proportion of N in the flag leaf was greater at anthesis compared to the other lines. These results suggest that a better understanding of the mechanisms determining N uptake at anthesis and post-anthesis N remobilization associated with senescence would offer scope to increase grain yield under N limiting conditions and/or combine high yield with high grain protein content in wheat cultivars under optimal N conditions
The reduction in grain yield (GY) in low N (LN) compared to high N (HN) conditions was 1.49 t ha−1 (−29.6%) in 2014 and 1.43 t ha−1 (−26.7%) in 2016 (P < 0.001; Table 2; Fig. 1), with an average reduction across years of 1.46 t ha−1 (−28.1%; P < 0.001; Fig. 1)
Summary
Wheat (Triticum aestivum L.) is the most widely grown cereal crop in the world, and accounts for 20% of the calories consumed by the global population (FAO, 2016). Global wheat production was 729 Mt in 2014 and in India was 96 Mt (FAO, 2016). India has the second highest global wheat production after China (FAO, 2016). The world population is predicted to reach 9 billion by 2050 and global demand for wheat is predicted to increase at an annual rate of ca. The rate of global yield increase in wheat is declining and is currently about 1.1% yr−1 (Hall and Richards, 2013). Future increases in grain yield will largely depend on raising above-ground biomass whilst maintaining harvest index
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