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Genotypic Variation in Grain P Loading across Diverse Rice Growing Environments and Implications for Field P Balances

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ABSTRACT

More than 60% of phosphorus (P) taken up by rice (Oryza spp.) is accumulated in the grains at harvest and hence exported from fields, leading to a continuous removal of P. If P removed from fields is not replaced by P inputs then soil P stocks decline, with consequences for subsequent crops. Breeding rice genotypes with a low concentration of P in the grains could be a strategy to reduce maintenance fertilizer needs and slow soil P depletion in low input systems. This study aimed to assess variation in grain P concentrations among rice genotypes across diverse environments and evaluate the implications for field P balances at various grain yield levels. Multi-location screening experiments were conducted at different sites across Africa and Asia and yield components and grain P concentrations were determined at harvest. Genotypic variation in grain P concentration was evaluated while considering differences in P supply and grain yield using cluster analysis to group environments and boundary line analysis to determine minimum grain P concentrations at various yield levels. Average grain P concentrations across genotypes varied almost 3-fold among environments, from 1.4 to 3.9 mg g−1. Minimum grain P concentrations associated with grain yields of 150, 300, and 500 g m−2 varied between 1.2 and 1.7, 1.3 and 1.8, and 1.7 and 2.2 mg g−1 among genotypes respectively. Two genotypes, Santhi Sufaid and DJ123, were identified as potential donors for breeding for low grain P concentration. Improvements in P balances that could be achieved by exploiting this genotypic variation are in the range of less than 0.10 g P m−2 (1 kg P ha−1) in low yielding systems, and 0.15–0.50 g P m−2 (1.5–5.0 kg P ha−1) in higher yielding systems. Improved crop management and alternative breeding approaches may be required to achieve larger reductions in grain P concentrations in rice.

No MeSH data available.


Theoretical relationship between grain yield and grain P concentration of a genotype grown across different environments or levels of P supply (full line with uncertainty interval indicated with dashed lines). The different zones on the curve can be interpreted as: (1) low grain yield and low grain P concentration—grain yield restricted by P availability; (2) low grain yield and medium to high grain P concentration—grain yield restricted by other factors; (3) high grain yield and medium grain P concentration—no major restrictions to grain yield; (4) high grain yield and luxury grain P loading—no major restrictions to grain yield and very high P supply. The critical range is the portion of the curve where yield declines quickly with declining grain P concentration.
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Figure 1: Theoretical relationship between grain yield and grain P concentration of a genotype grown across different environments or levels of P supply (full line with uncertainty interval indicated with dashed lines). The different zones on the curve can be interpreted as: (1) low grain yield and low grain P concentration—grain yield restricted by P availability; (2) low grain yield and medium to high grain P concentration—grain yield restricted by other factors; (3) high grain yield and medium grain P concentration—no major restrictions to grain yield; (4) high grain yield and luxury grain P loading—no major restrictions to grain yield and very high P supply. The critical range is the portion of the curve where yield declines quickly with declining grain P concentration.

Mentions: A typical nutrient response curve is characterized by an ascending area of the curve where yield increases with plant nutrient concentration, and a relatively level portion where yield is not limited by the specific nutrient (Bates, 1971). The portion of the curve where yield declines quickly with declining nutrient concentration is referred to as the “critical range.” Based on this, a theoretical relationship between grain yield and grain P concentration for a certain rice genotype grown across different environments or levels of P supply was drawn in Figure 1. In P-deficient environments, grain yield is limited by insufficient P uptake and this affects grain P concentrations which remain low (zone 1 on Figure 1). When P supply increases, increases in grain P concentration will depend on whether grain yield increases concomitantly. If other factors limiting grain yield exist, additional P available in the plant tissue will be distributed among a small amount of grain biomass and grain P concentrations may ultimately reach high levels (zone 2). In environments where P deficiency is the main yield-limiting factor, additional P uptake will lead to increases in grain P concentration and grain yield but—compared to zone 2—the additional P moving to grain may be partly diluted because of the grain yield increase (zone 3). Lastly, if P supply is in excess of that required by the crop for optimal growth, luxury P loading in grains at concentrations above the sufficiency range may occur (zone 4).


Genotypic Variation in Grain P Loading across Diverse Rice Growing Environments and Implications for Field P Balances
Theoretical relationship between grain yield and grain P concentration of a genotype grown across different environments or levels of P supply (full line with uncertainty interval indicated with dashed lines). The different zones on the curve can be interpreted as: (1) low grain yield and low grain P concentration—grain yield restricted by P availability; (2) low grain yield and medium to high grain P concentration—grain yield restricted by other factors; (3) high grain yield and medium grain P concentration—no major restrictions to grain yield; (4) high grain yield and luxury grain P loading—no major restrictions to grain yield and very high P supply. The critical range is the portion of the curve where yield declines quickly with declining grain P concentration.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC5037189&req=5

Figure 1: Theoretical relationship between grain yield and grain P concentration of a genotype grown across different environments or levels of P supply (full line with uncertainty interval indicated with dashed lines). The different zones on the curve can be interpreted as: (1) low grain yield and low grain P concentration—grain yield restricted by P availability; (2) low grain yield and medium to high grain P concentration—grain yield restricted by other factors; (3) high grain yield and medium grain P concentration—no major restrictions to grain yield; (4) high grain yield and luxury grain P loading—no major restrictions to grain yield and very high P supply. The critical range is the portion of the curve where yield declines quickly with declining grain P concentration.
Mentions: A typical nutrient response curve is characterized by an ascending area of the curve where yield increases with plant nutrient concentration, and a relatively level portion where yield is not limited by the specific nutrient (Bates, 1971). The portion of the curve where yield declines quickly with declining nutrient concentration is referred to as the “critical range.” Based on this, a theoretical relationship between grain yield and grain P concentration for a certain rice genotype grown across different environments or levels of P supply was drawn in Figure 1. In P-deficient environments, grain yield is limited by insufficient P uptake and this affects grain P concentrations which remain low (zone 1 on Figure 1). When P supply increases, increases in grain P concentration will depend on whether grain yield increases concomitantly. If other factors limiting grain yield exist, additional P available in the plant tissue will be distributed among a small amount of grain biomass and grain P concentrations may ultimately reach high levels (zone 2). In environments where P deficiency is the main yield-limiting factor, additional P uptake will lead to increases in grain P concentration and grain yield but—compared to zone 2—the additional P moving to grain may be partly diluted because of the grain yield increase (zone 3). Lastly, if P supply is in excess of that required by the crop for optimal growth, luxury P loading in grains at concentrations above the sufficiency range may occur (zone 4).

View Article: PubMed Central - PubMed

ABSTRACT

More than 60% of phosphorus (P) taken up by rice (Oryza spp.) is accumulated in the grains at harvest and hence exported from fields, leading to a continuous removal of P. If P removed from fields is not replaced by P inputs then soil P stocks decline, with consequences for subsequent crops. Breeding rice genotypes with a low concentration of P in the grains could be a strategy to reduce maintenance fertilizer needs and slow soil P depletion in low input systems. This study aimed to assess variation in grain P concentrations among rice genotypes across diverse environments and evaluate the implications for field P balances at various grain yield levels. Multi-location screening experiments were conducted at different sites across Africa and Asia and yield components and grain P concentrations were determined at harvest. Genotypic variation in grain P concentration was evaluated while considering differences in P supply and grain yield using cluster analysis to group environments and boundary line analysis to determine minimum grain P concentrations at various yield levels. Average grain P concentrations across genotypes varied almost 3-fold among environments, from 1.4 to 3.9 mg g−1. Minimum grain P concentrations associated with grain yields of 150, 300, and 500 g m−2 varied between 1.2 and 1.7, 1.3 and 1.8, and 1.7 and 2.2 mg g−1 among genotypes respectively. Two genotypes, Santhi Sufaid and DJ123, were identified as potential donors for breeding for low grain P concentration. Improvements in P balances that could be achieved by exploiting this genotypic variation are in the range of less than 0.10 g P m−2 (1 kg P ha−1) in low yielding systems, and 0.15–0.50 g P m−2 (1.5–5.0 kg P ha−1) in higher yielding systems. Improved crop management and alternative breeding approaches may be required to achieve larger reductions in grain P concentrations in rice.

No MeSH data available.