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Can grain protein contents be increased without sacrificing grain yields in wheat?

Senthold Asseng and Stephen Milroy

CSIRO Plant Industry, Private Bag 5, PO Wembley WA 6913, Australia, Senthold.Asseng@csiro.au

Abstract

Genetic potential for grain protein concentration in wheat has previously been shown to be negatively correlated to genetic yield potential. In a simulation analysis, when the potential rate for grain dry matter accumulation was increased to reflect an increase in the genetic yield potential, grain protein concentration declined linearly with increasing yield under optimal water and N supply. Introducing single constraints by increasing temperatures, water shortage or sub-optimal N supply shifted the line but the linear negative relationship was maintained. This close linear negative relationship between grain protein concentration and grain yield agrees well with published experimental findings and highlights the genetic limitation to increases in grain protein. However, simulating co-limitation of water and N, which is common in Mediterranean agriculture of Western Australia, indicated that the relationship can become non-linear in some situations: as yield potential decreased, the simulated grain yield achieved did not change but grain protein increased. From this result it can be hypothesised that in situations were both water and N are limiting, genotypes with a slightly lower genetic potential yield may deliver higher grain protein without compromising the achievable grain yield as limited by environment. The hypothesis needs to be tested under controlled and field conditions.

Key words

APSIM, grain protein, yield potential, wheat

Introduction

With increasing attention to food quality in recent years, grain protein concentration has increased in importance. However, gains in genetic yield potential in the last decades have decreased the genetically-determined grain protein concentration potential and attempts to increase the potential grain protein concentration often resulted in a reduction in yield potential (Oury et al. 2003). A simulation model was used together with long term historical weather records to explore the trade-off between yield and protein concentration with changing the genetic yield potential in a water and nitrogen limited Mediterranean environment.

Methods

The Agricultural Production Systems SIMulator (APSIM) (Keating et al. 2003) for wheat (Triticum aestivum L.) (APSIM-Nwheat version 1.55s) is a crop simulation model, consisting of modules that incorporate aspects of soil water, nitrogen, crop residues, crop growth and development and their interactions within a crop/soil system that is driven by daily weather data. A detailed description of APSIM-Nwheat is given by Asseng (2004). Recent advances in simulating grain protein concentrations in wheat (Asseng et al. 2002) now allow the analysis of the impact of yield-related physiological traits on grain protein concentration. Grain protein concentrations often vary between seasons in Mediterranean environments and are affected by high temperatures and terminal water shortage during grain filling. In a simulation experiment with APSIM, a trait for increased grain filling rate, which has been suggested as increasing yields of lupin in terminal drought environments (Palta et al. 2005) has been used to explore the expected trade-off between yield and protein concentration with changing the genetic yield potential in wheat.

Results and Discussion

The variation between different seasons in the protein-yield curves with the increased potential grain filling rate indicated a large impact of rainfall, and consequently water and water by N interaction, on this relationship (Figure 1). The simulated changes in protein content with no change in grain yield in particularly in the low yielding seasons were unexpected, but can be explained by the model through an intermittently restricted carbohydrate supply that occurred at different frequency with the different grain filling rates. Hence, N accumulation, which is constrained by periods of low grain dry matter accumulation, was interrupted to varying extents. The frequency of changes in protein content without change in yield was lower at high N supply and at high rainfall locations (Asseng and Milroy 2006). From these responses it is hypothesised that a higher genetic grain protein potential could be achieved via a lower genetic yield potential without compromising the achievable grain yield under water- and N-limited conditions. Cultivars with moderate yield potential might therefore be more suitable for growth-limited environments: attaining a higher grain protein but still achieving the environmental yield potential.

Figure 1. Simulated relationship between grain protein percentage and grain yield with seven different potential grain filling rates (rates increase with increasing yield or decreasing protein) for 104 years (lines connect the different filling rates) at Merredin (low rainfall location), Western Australia, with 60 kg N/ha.

References

Asseng, S., Bar-Tal, A., Bowden, J.W., Keating, B.A., Van Herwaarden, A., Palta, J.A., et al., 2002. Simulation of grain protein content with APSIM-Nwheat. European Journal of Agronomy, 16, 25-42.

Asseng, S., 2004. Wheat crop systems – A simulation analysis. CSIRO Publisher, Melbourne, ISBN 064309119X, pp. 275

Asseng, S. and Milroy, S.P., 2006. Simulation of environmental and genetic effects on grain protein concentration in wheat. European Journal of Agronomy (in press)

Keating, B.A., Carberry, P.S., Hammer, G.L., Probert, M.E., Robertson, M.J., Holzworth, D., et al., 2003. An overview of APSIM, a model designed for farming systems simulation. European Journal of Agronomy, 18, 267-288.

Oury, F.X., Berard, P., Brancourt-Hulmel, M., Depatureaux, C., Doussinault, G., Galic, N., Giraud, A., Heumez, E., Lecomte, C., Pluchard, P., Rolland, B., Rousset, M., Trottet, M., 2003. Yield and grain protein concentration in bread wheat: a review and a study of multi-annual data from a French breeding program. J. Genet. Breed. 57, 59-68.

Palta, J.A., Nandwal, A.S., Kumari, S. and Turner, N.C., 2005. The yield performance of lupin genotypes under terminal drought in a Mediterranean-type environment. Australian Journal of Agricultural Research, 55, 449-459.

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