The changes in climate that are predicted to occur during the next century present many challenges to sustainable crop production and food security. A burgeoning world population accompanied by increasing standards of living is expected to require increased levels of production of food, fiber, and industrial crops. This needs to be achieved with little further increase in the area of arable land and with finite and increasingly expensive supplies of fertilizer. These challenges have brought the importance of plant nutrition to sustainable agricultural production into sharp focus and have highlighted the need to improve nutrient use efficiency (NUE).
NUE is defined as the yield per unit nutrient supplied, and it has two components: (1) the ability to extract nutrients from the soil (uptake efficiency), and (2) the ability to convert the nutrients absorbed by the crop into grain (utilization efficiency). If breeding for improved NUE is to be successful, a number of conditions need to be met, such as the presence of useful genetic variation in NUE, understanding the genetic basis of the traits, and defining appropriate selection criteria. This often requires a clear understanding of the important physiological determinants of nutrient efficiency.
The development of green super rice varieties with improved nutrient use efficiency (NUE) is a vital target to increase yield and make it more stable under rainfed conditions. By following an early backcross (BC) breeding approach using a high-yielding and widely adapted Xian variety, Weed Tolerant Rice 1 (WTR-1), as a recipient and a Geng variety, Hao-An-Nong (HAN), as a donor, selection began from the BC1F2 generation followed by four generations of progeny testing under different nutrient conditions. Thus, selected promising lines can be useful resources for molecular genetic dissection.
Oilseed rape is one of the important field crops in the world, and its production requires high nitrogen fertilization. Hence, increased nitrogen uptake efficiency in this crop is a high priority for sustainable agriculture. A comprehensive study of macro-physiological characteristics associated with breeding progress, conducted under contrasting nitrogen fertilization levels in a large panel of elite oilseed rape varieties representing breeding progress over the past 20 years, indicated that increased plant biomass at flowering, along with increases in primary yield components, has increased NUE in modern varieties. Nitrogen uptake efficiency has improved through breeding, particularly at high nitrogen.
The rapid development of an array of molecular and genomic techniques such as marker-assisted selection, CRISPR-Cas9, and other advanced breeding approaches is expected to provide an opportunity to overcome many hurdles that have hindered progress so far. Marshaling new methods and technologies with traditional disciplines of plant breeding, crop physiology, and agronomy is expected to provide expanded opportunities to study genetic differences in NUE and to link genotype to phenotype.
References:
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JEWEL, Z., ALI, J. AND PANG, Y., 2018, Developing green super rice varieties with high nutrient use efficiency by phenotypic selection under varied nutrient conditions. Crop J., 7: 368–377.
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LIGHTFOOT, D.A., 2018, Developing crop varieties with improved nutrient-use efficiency. Engineering Nitrogen Utilization in Crop Plants, 1:1-11.
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STAHL, A., VOLLRATH, P., SAMANS, B., FRISCH, M., WITTKOP, B. AND SNOWDON, R.J., 2019, Effect of breeding on nitrogen use efficiency-associated traits in oilseed rape. J. Exp. Bot., 70(6):1969-1986.
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