फसल सुधार के लिए विकिरण उपयोग दक्षता का दोहन

The energy of the entire ecosystem is reliant on the sun, which is the sole source of energy for all living organisms, directly or indirectly. Solar radiations reach from sun to earth and helps in photosynthesis, a process by which plants transform light energy into chemical energy.

The rate of accumulation of dry matter of all plants is completely dependent on the interception of light energy from the sun (400–700 nm wavelength range), known as photosynthetically active radiation (PAR). Global climate changes are affecting crop yield potential and reducing the yield of crop significantly.

A rapid rise in population is expected in the near future (about 10 billion by 2050), which might raise food consumption and put load on the agricultural system. So, we need to improve the efficiency of crop varieties to produce more yield with less resources. Crop productivity is the outcome of the amount of radiation, water, or nutrients captured by the crop and how efficiently those resources are used, which could only be enhanced by improving the traits related to yield and biomass production, such as Radiation use efficiency (RUE).

RUE is the efficiency of the crop plant for using intercepted radiation to produce the biomass of the plant. With the increased correlation between biomass production and radiation interception the crop production can be heightened.

RUE is measured by the device known as Ceptometer. It is light-weight, portable and has linear photosynthetically active radiation (PAR) sensor. Its measurement ranges from 0 to > 2,500 μmol m^-2s^-1. Formula to calculate RUE is

RUE=      Biomass accumulation / Photosynthetically Active Radiation

Scope to improve RUE in agricultural crops

Yield potential of any crop is associated with intercepted radiation, conversion into biomass and allocation to edible organs. But the photosynthetic conversion of light into biomass is currently less than half the theoretical maximum in many major food crops. Hence, there is a wide scope to improve RUE in crops, which could be explained a follows

• From the total solar radiation only 3-6 % of solar energy is utilized by the plants and most of solar energy remains unutilized.
• RUE is also related to the other physiological traits like, Water Use Efficiency and Net Assimilation Rate which simultaneously increases with increased RUE.
• For making climate smart crops enhanced RUE is very much essential.
• Wheat yield potential can be improved by up to 25% through improvement of RUE (Reynold et al., 2010).

RUE of different crops

The RUE studies in field crops are still in very nascent stage and the information is available for very few crops (Table 1). Among the studied crops RUE is found to be highest in Potato as mentioned below.

RUE value of different crops

 Factors affecting RUE

• Photosynthetic traits
• Canopy Architecture
• Transport of assimilates
• Other environmental factors like light, temperature and nutrient availability mainly nitrogen

 Suggested Targets for improving Radiation Use Efficiency

• Plant Phenology
• Partitioning of assimilates
• Leaf photosynthesis
• Non-leaf photosynthesis
• Metabolic efficiency
• Efficiency of light-limited tissue
• Canopy architectural characteristics

Strategies to improve radiation use efficiency

RUE increases with increasing rate of leaf photosynthesis and decreases with increasing leaf age, respiration and some other inherent factors. In many studies, a linear relationship has been found between intercepted photosynthetically active radiation (IPAR), leaf area index (LAI), leaf area duration (LAD), and biomass production in many agricultural crops such as barley, wheat, poplar, willow, maize, and oilseed rape.

Based on the factors affecting RUE there are a number of approaches which can be utilized to improve it. Most of the research aimed at increasing yield through photosynthesis has concentrated on increasing the RUE of individual organs, essentially the leaves, through higher rates of photosynthesis per unit organ area.

Mathan et al., (2021) revealed that in cultivated rice varieties there could be many targets for improving the photosynthetic efficiency, such as, rubisco activity, electron transport rate, and leaf anatomical.

Variations in vascular features, sucrose transport, and functions of sugar metabolic enzymes explained the differences in source–sink relationships between cultivated rice, Nipponbare and a wild rice O. australiensis, these could also be targeted to improve the RUE. Lu et al., (2020) compared the grain yield, IPAR and RUE of hybrid rice and inbred rice under different N rates and planting densities and found the maximum radiation use efficiency with high planting density.

Wheat plants that were genetically manipulated to increase leaf photosynthesis through a higher activity of the Calvin cycle’s enzymes also reported higher rates of ear assimilation, which translated into increased grain yield (Driever et al., 2017; Simkin et al., 2020). Besides these there are numerous other approaches which are targeted by the agricultural scientists for increasing RUE in crop plants and they are categorized as follows:

Physiological approach:

• Manipulating CO₂ diffusion, like stomatal conductance (g_s) and mesophyll conductance (g_m)
• Increasing non-leaf photosynthesis like, ear photosynthesis and panicle photosynthesis
• Enhancing the efficiency of photosystems
• Retranslocation of assimilates, like increasing sink strength and increasing nutrient supply

Biochemical approach:

• Increased activity of sedoheptulose1,7-bisphosphatase
• Improving kinetic properties of RuBisCO
• Increasing photoprotection of PSII through non photochemical quenching
• Enhancing the kinetic properties of key photosynthetic enzymes such as, RuBisCO, Sedoheptulose 1,7-bisphosphate and Fructose 1,6-bisphophate aldolase

Anatomical approach:

• Introduction of the proto-kranz anatomy in C₃
• Introduction of C₄ like anatomy in C₃ plants
• Increasing the size of mesophyll cell
• Increasing vein density

Molecular approach:

• Introducing the carbon concentrating mechanism (CCM) in C₃ crops through Agrobacterium transformation example; ictB gene (Inorganic carbon transporter from Cynobacteria)
• Overexpression of genes involved in the activity of Calvin cycle’s enzymes, SBPase gene
• Direct installation of enzymes involved in C₄ metabolism into C₃ crop species like, NADP-ME, MDH and PPDK
• Overexpression of maize MADS-box transcription gene zmm28

Conclusion

RUE is a potentially useful trait for crop improvement, as it is currently less explored and utilized in breeding progamme of major crops. Climate change and sunshine variations during crop period offers challenge for screening genotypes for RUE under field conditions.

But, there is an urgent need for identifying genotypes and germplasm for high RUE in different crops for sustainable agriculture. Crop canopy architecture, photosynthetic traits, leaf anatomical traits, source and sink traits contribute significantly for improving RUE in crops. However, there are numerous research areas that may be investigated in order to discover new pathways for increasing RUE.

References:

• Reynolds, M., Bonnett, D., Chapman, S. C., Furbank, R. T., Manès, Y., Mather, D. E. & Parry, M. A. (2011). Raising yield potential of wheat. I. Overview of a consortium approach and breeding strategies. Journal of experimental botany, 62(2), 439-452.
• Furbank, R. T., Sharwood, R., Estavillo, G. M., Silva-Perez, V. & Condon, A. G. (2020). Photons to food: genetic improvement of cereal crop photosynthesis. Journal of Experimental Botany, 71(7), 2226-2238.
• Araus, J. L., Sanchez-Bragado, R. & Vicente, R. (2021). Improving crop yield and resilience through optimization of photosynthesis: panacea or pipe dream?. Journal of Experimental Botany, 72(11), 3936-3955.
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• Ermakova, M., Arrivault, S., Giuliani, R., Danila, F., Alonso Cantabrana, H., Vlad, D. & Furbank, R. T. (2021). Installation of C₄ photosynthetic pathway enzymes in rice using a single construct. Plant biotechnology journal, 19(3), 575-588.
• Driever, S. M., Simkin, A. J., Alotaibi, S., Fisk, S. J., Madgwick, P. J., Sparks, C. A. & Raines, C. A. (2017). Increased SBPase activity improves photosynthesis and grain yield in wheat grown in greenhouse conditions. Philosophical Transactions of the Royal Society B: Biological Sciences, 372(1730).
• Hubbart, S., Smillie, I. R., Heatley, M., Swarup, R., Foo, C. C., Zhao, L. & Murchie, E. H. (2018). Enhanced thylakoid photoprotection can increase yield and canopy radiation use efficiency in rice. Communications Biology, 1(1), 1-12.
• Sadras, V. O. & Calderini, D. (Eds.). (2020). Crop Physiology Case Histories for Major Crops. Academic Press.
• Hatfield, J. L., & Dold, C. (2019). Photosynthesis in the solar corridor system. In The solar corridor crop system(pp. 1-33). Academic Press.
• Miralles, D. J., Abeledo, L. G., Prado, S. A., Chenu, K., Serrago, R. A. & Savin, R. (2021). Barley. In Crop Physiology Case Histories for Major Crops(pp. 164-195). Academic Press.
• Mattera, J., Romero, L.A., Cuatrín, A.L., Cornaglia, P.S., Grimold, A.A., (2013). Yield components, light interception and radiation use efficiency of Lucerne (Medicago sativa) in response to row spacing. Euroupian Jorunal of Agronomy. 45, 8795.
• Lizana, X. C., Sandaña, P., Behn, A., Ávila-Valdés, A., Ramírez, D. A., Soratto, R. P. & Campos, H. (2021). Potato. In Crop Physiology Case Histories for Major Crops(pp. 550-587). Academic Press.

Authors

Preety Dohrey, Mamrutha HM, Rinki, Kapil Deswal, Zeenat Wadhwa and Yogesh Kumar

ICAR-Indian Institute of Wheat and Barley Research Karnal, 132001 (Haryana)

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