Elsevier

European Journal of Agronomy

Volume 92, January 2018, Pages 17-29
European Journal of Agronomy

Research paper
Trade-off between grain weight and grain number in wheat depends on GxE interaction: A case study of an elite CIMMYT panel (CIMCOG)

https://doi.org/10.1016/j.eja.2017.09.007Get rights and content

Highlights

  • TGW and GN across 27 elite CIMMYT genotypes showed contrasting associations between locations.

  • The trade-off between TGW and GN was affected by the environmental conditions during grain growth.

  • A low trade-off between TGW and GN was due to heavier IGW of both proximal and distal grain position of the spike.

  • Different breeding strategies aimed at increasing grain yield are suggested depending on the TGW-GN interaction.

Abstract

Identifying the functionally linked mechanisms of grain yield (GY) and its components —i.e. grain number (GN) and grain weight (GW) is necessary for boosting GY potential of wheat. The objectives of the current study were to: (i) analyze the trade-off between GW and GN in 27 elite wheat genotypes grown in two contrasting locations with different yield potential, (ii) assess its causes, and (iii) gain a better understanding of the physiology behind the trade-off between GW and GN. A set of 27 elite wheat genotypes was evaluated during three years in Ciudad Obregón, Mexico (CO), and two years in Valdivia, Chile (Val). GY was higher in Val than CO (783 g m−2 and 665 g m−2, respectively) and positively associated with above-ground biomass (BM) in both locations. In CO, 15,850 grains m−2 were recorded and 15,197 grains m−2 in Val, while thousand-grain weight (TGW) was higher (P < 0.001) in Val than in CO by 23% (52.2 and 42.5 g, respectively). Also, individual grain weight (IGW) of most categories was higher in Val than in CO. Remarkably, the relationships between GY and GN showed contrasting responses between locations despite the similar GN. A very low GY/GN relationship was found in CO, while a positive and linear relationship was plotted in Val. The virtual lack of association found in CO (11%) was due to a clear trade-off between TGW and GN, while the positive association in Val was the result of a very low trade-off between the two main yield components. Interestingly, the IGW of grains set in the G2 and G4 positions showed negative association with GN in CO across years as well as during each year, while in Val no association was found across years, though a very low association was found in each year. The source-sink treatments applied ten days after anthesis by halving the spikes showed that, G2 and G4 responded to the increased source by 7.7% and 16%, respectively in CO, while in Val the responses were 15% and 5.1% in Valy13 and 6.5% and 9.6% in Valy14, respectively. In conclusion, the lack of association between GY and GN found in CO was due to the trade-off between the two main yield components (GW and GN), which was mainly explained by higher average temperature and lower photothermal quotient during grain filling recorded in this location than in Val. These results highlight the need to employ different strategies aimed at increasing yield potential depending on the environment. The increase of grain number could be proposed for environments with favorable growing conditions as in Val. On the contrary, increasing GW would be the objective in environments with little chance of taking advantage of increased GN such as CO.

Introduction

During the “Green Revolution” a quantum leap in wheat yield was achieved through improved biomass partitioning as a result of introgressing the Rht1 and Rht2 alleles. This, in turn, improved grain yield, harvest index and grain number due to the higher amount of assimilate partitioned to the spike during pre-flowering (Miralles et al., 1998, Slafer and Andrade, 1993). However, genetic gains in yield potential are currently well under 1% per year (Crespo-Herrera et al., 2017), and global wheat production would have to increase ∼2.4% per year to feed the increasing human population (Ray et al., 2013), underlining the need to accelerate genetic gains. Studies published recently have reported that grain yield (GY) of wheat and other crops are asymptotically related to grain number (GN) suggesting that GY tends to level off at a very high GN (Bomford, 2009, Bustos et al., 2013, García et al., 2013), which could be ascribed to the trade-off between grain weight (GW) and GN. This trade-off could be due to: (i) source limitation during grain filling (Sinclair and Jamieson, 2006), (ii) the setting of smaller grains in distal position of the spikes, with lower weight potential (Acreche and Slafer, 2006, Fischer, 2008), or (iii) a combination of both. The former assumes source limitation during grain filling while the latter could be related either to source limitations at pre-grain filling or to intrinsic limitations in the grain weight potential of distal grain positions (Acreche and Slafer, 2006).

Taking into account the negative relationship generally reported between TGW and GN in wheat (Acreche and Slafer, 2006, Bustos et al., 2013, García et al., 2013, Miralles and Slafer, 1995, Sadras, 2007, Slafer and Miralles, 1993) and other grain crop species (Bulman et al., 1993, Gambín and Borrás, 2010, López Pereira et al., 1999), future increases of yield potential both in wheat as well as other crops could be achieved by improving individual grain weight (IGW) as a necessary breeding strategy to counteract the trade-off between the two main yield components (Calderini and Ortiz-Monasterio, 2003). Therefore, to quantify the degree of the trade-off between the two major yield components of wheat, and to understand the causes behind the negative association between TGW and GN, is a key for wheat breeding efficiency aimed at continuing increasing grain yield. Recent published evidences suggest that the trade-off between TGW and GN could be affected by the environment taking into account that the relationship between these yield components showed different values in the same wheat doubled haploid population across the explored environments (Bustos et al., 2013, García et al., 2013). Although the trade-off between TGW and GN has been reported since long ago (e.g. Villareal et al., 1992) little is known about the environmental effect on this association. This information can provide important knowledge for wheat breeding strategies aimed at different kinds of high yielding environments.

The objectives of the current study were to (i) gain a better understanding of the trade-off between GW and GN and its interaction with the environment in 27 elite wheat genotypes from the CIMMYT Core Germplasm (CIMCOG) population grown in two contrasting locations (both corresponding to mega-environment 1) and (ii) assess its physiological bases. The answer to these objectives would accelerate the breeding of wheat with higher grain yield potential.

Section snippets

Plant material

A set of 27 elite wheat genotypes [26 Triticum aestivum (22 elite lines, 4 historic lines) and 1 T. turgidum var. durum] from the CIMMYT Core Germplasm (CIMCOG) panel were provided by CIMMYT’s breeding programs (Table A1). The 27 genotypes were selected because they represent historical genetic gains and similar phenology. Some lines are synthetic-derived wheat materials, and one is a recently released and extremely high yielding durum wheat (Table A1). Five field trials in two locations (three

Weather conditions during the crop cycles at both experimental locations

The mean time span of the Em-Ant period was shorter in Val than in CO both in days (64 and 88 days, respectively) and thermal time units (787°Cd in Val and 1387°Cd in CO, respectively), while the Ant-PM phase was similar between these locations, i.e. 41 days and 788°Cd in CO; and 45 days and 725°Cd in Val, respectively (Table A2, Table A3). Differences in the Em-Ant period between CO and Val could have been due to the different photoperiod experienced by plants as longer days were recorded in Val

Discussion

Differences in GY were expressed at both locations as expected, with Val being the highest yielding environment. These results agree with a previous study conducted by García et al. (2013) where southern Chile (Val) showed higher GY potential than CO. Differences in yield potential between Val and CO were recorded in spite of the shorter crop cycle in Val (4 months) than in CO (5 months). The higher development rate found in Val was mainly due to the longer photoperiod between emergence and

Conclusions

The results of the present study, which assessed 27 elite wheat genotypes grown in CO and Val, show a significant trade-off between the two main yield components (GW and GN) in CO. The need to increase GW is a clear consequence of this trade-off, which is highlighted by the weak association between GY and GN recorded in CO during each of the three growing seasons evaluated here. On the other hand, very low trade-off between GW and GN was found in Val across the 27 elite wheat genotypes, given

Acknowledgments

We would like to thank the Wheat Physiology Department of the International Maize and Wheat Improvement Center (CIMMYT); the Institute of Plant Production and Plant Protection of the Universidad Austral de Chile and the personnel of the EEAA (UACh) experiment station. The research was supported by funding from Mexico’s Ministry of Agriculture (Secretaria de Agricultura, Ganaderia, Desarrollo Rural, Pesca y Alimentación, SAGARPA) and the Sustainable Modernization of Traditional Agriculture

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