High-Impact Research

BNI-enabled wheat is nitrogen-efficient and maintains productivity

Related Research Project
BNI-system

Description

The amount of nitrogen fertilizer used in modern agriculture is enormous, amounting to about 120 million tons worldwide. However, most of it (about 70%) is not absorbed by crops and is leached out from farmland, making farmland a source of pollution to the aquatic environment and emission of nitrous oxide (N2O), a global warming gas with a greenhouse effect up to 298 times greater than that of carbon dioxide. The release of excess nitrogen into the environment is related to nitrification in the soil. Nitrification is a microbial oxidation reaction from ammonia-form nitrogen (NH4+-N) to nitrate-form nitrogen (NO3--N), which is an important pathway in the nitrogen cycle of the earth. NH4+ is retained in the soil and does not migrate much, while NO3- is weakly bound to the soil and is highly mobile, so it easily leaches out of the farmland. Nitrification in agricultural soils is highly active due to a large amount of industrially fixed nitrogen fertilizer applied, so the conversion to NO3-, which cannot be retained by the soil, and its leaching into the hydrosphere proceed rapidly, and N2O is released into the atmosphere during the process (Fig. 1 left).

Therefore, if the nitrification rate of agricultural soil can be suppressed, it could be an effective means of solving the problem. Biological Nitrification Inhibition (BNI) is the process by which crops themselves secrete substances that inhibit nitrification. BNI technology that utilizes BNI can both maintain and increase crop yields with less nitrogen fertilizer input and reduce environmental impact. By inhibiting nitrification, crops have more opportunities to absorb nitrogen, which allows reducing NO3- leaching and N2O release. The introduction or enhancement of BNI capacity through breeding can be expected to both reduce agricultural greenhouse gas emissions and nitrogen fertilizer application.

We have been investigating the BNI potential of wheat, a major cereal covering the largest area among food crops, and developed BNI-enabled wheat by introducing superior BNI capacity from Leymus racemosus into high-yielding wheat varieties through chromosome engineering tools. Substitution of Leymus racemosus chromosome N short-arm with wheat chromosome 3B introduced BNI capacity, and the resulting line was further back-crossed with high-yielding varieties. (Fig. 2) The BNI-enabled variety, “BNI-Munal,” showed around 2–5 times higher BNI capacity than the parental variety, “Munal.” This high-yielding background ”BNI-Munal” showed suppression of nitrifying microorganisms in rhizosphere soil, resulting in the lowering of soil nitrification rate and N2O emission (Fig. 3); therefore, the environmental load by agriculture caused by nitrogen fertilizer can be reduced. “BNI-Munal” also showed efficient use of NH4+ in terms of nitrogen assimilation and soil organic nitrogen. “BNI-Munal” showed a significantly higher yield than Munal, and a 60% reduction in nitrogen application (from 250 to 100 kgN/ha) did not show a difference in yield between BNI-enabled and parental variety, hence the grain protein content (and bread-making quality) also did not change (Fig. 3). Further improvement in BNI capacity can be made by reducing the N chromosome short-arm and elucidating the mode of action, which is ongoing.

 

Figure, table

  1. Fig1

    Fig. 1. BNI-enabled wheat with Leymus racemosus N chromosome (ex. BNI-Munal)

     

  2. Fig2

    Fig. 2. N2O emission from BNI-enabled Munal
    N2O emission was suppressed by 25%.

     

  3. Fig3

    Fig. 3. Changes in nitrogen assimilation
    BNI-enabled wheat prefers ammonium.

     

  4. Fig4

    Fig. 4. Grain yield under different nitrogen
    No significant difference in yields between Munal-control at 250 kg/ha and BNI-enabled Munal at 100 kg/ha.

     

  5. Fig5

    Fig. 5. Bread making quality of BNI-enabled wheat
    BNI-enabled Munal can be processed into bread as well as Munal-control.

     

    Figures reprinted/modified with permission from Subbarao et al. (2021).

     

     

Classification

Technical

Research project
Program name

Environment

Term of research

FY 2021–2025

Responsible researcher

Subbarao Guntur Venkata ( Crop, Livestock and Environment Division )

KAKEN Researcher No.: 00442723

Kishii Masahiro ( International Maize and Wheat Improvement Center )

KAKEN Researcher No.: 70535476

Oritz-Monasterio Ivan ( International Maize and Wheat Improvement Center )

Gao Xiang ( Crop, Livestock and Environment Division )

Itria Ibba Maria ( University of the Basque Country )

Karwat Hannes ( International Maize and Wheat Improvement Center )

Gonzalez-Moro M. B. ( University of the Basque Country )

Gonzalez-Murua Carmen ( University of the Basque Country )

Tadashi Yoshihashi ( Biological Resources and Post-harvest Division )

KAKEN Researcher No.: 60450269
MIERUKA ID: 001766

Tobita Satoshi ( Nihon University )

KAKEN Researcher No.: 30450266

Kommerell Victor ( International Maize and Wheat Improvement Center )

Braun Hans-Joachim ( International Maize and Wheat Improvement Center )

Iwanaga Masa ( 顧問 )

ほか
Publication, etc.

Subbarao et al. (2021) PNAS 118: e2106595118
https://doi.org/10.1073/pnas.2106595118

Japanese PDF

2021_A04_ja.pdf459.8 KB

English PDF

2021_A04_en.pdf293.84 KB

Poster PDF

2021_A04_poster.pdf359.92 KB

* Affiliation at the time of implementation of the study.