ReviewA global analysis of dry matter accumulation and allocation for maize yield breakthrough from 1.0 to 25.0 Mg ha−1
Graphical abstract
Introduction
Maize (Zea mays L.) is the largest food crop in the world in terms of both grain yield per hectare and total production (Tester and Langridge, 2010; Hou et al., 2020; Hou et al., 2021a). The primary countries for maize production are the USA, China, Brazil, Argentina, etc., and the average yield is 5.8 Mg ha−1 in the global world (FAO, 2020). Maize production consumes great amounts of water and fertilizers, and produces massive straw, which is an important biofuel feedstock (Liu et al., 2022a). With the growth of the world economy and the increasing consumption of fossil fuels, the demand for biofuel will continue to increase (Mauser et al., 2015). The current increases in crop yields in the limited arable land are still not sufficient to satisfy the demands of the world's population by 2050 (Bailey-Serres et al., 2019). Therefore, increasing maize production per unit area is not only vital for future food security, but also for increasing resources use efficiency. It is also a critical approach to achieve the United Nations Sustainable Development Goal SDG 2 (Zero Hunger) (FAO, 2015).
In recent decades, more and more studies have demonstrated that increasing population density is one of the most effective ways to improve maize grain yield (Zhang, 2011; Liu et al., 2017; Assefa et al., 2018; Hou et al., 2020; Luo et al., 2020; Jaikumar et al., 2021; Rizzo et al., 2022). A recent study stated that by increasing the plant density by 15,000 plants ha−1 without extra nitrogen input, the maize grain yield could increase by 2.7% – 10.5% in China (Hou et al., 2020). This improvement of grain yield is mainly due to the fact that increasing plant density can improve light interception, photosynthesis, and light use efficiency and thus increase the aboveground dry matter (DM) accumulation and final grain yield (Maddonni et al., 2001; Li et al., 2011; Huang et al., 2017; Xu et al., 2017; Bernhard and Below, 2020).
The accumulated DM or photosynthate is the material base of yield formation. Increasing the total DM accumulation and the proportion of DM allocated to the kernels are the key factors for yield improvement (Rivera-Amado et al., 2019). A previous study with multisite experiments showed that the contribution of DM to grain yield was 73.7%, indicating it played an important role in varieties with a high yield level (Liu et al., 2020a). Many studies have pointed out that DM accumulation during post-sillking (from silking to maturity) is more important for modern maize cultivars (Yang et al., 2012; Zhou et al., 2016; Liu et al., 2017; Cao et al., 2021). The proportion of post-silking DM is more than 60% when the grain yield is > 18 Mg ha−1, which is only 50% when the grain yield is < 9.0 Mg ha−1 (Meng et al., 2018). Therefore, higher DM accumulation or the proportion of post-silking DM is vital for achieving higher grain yields.
Previous studies showed that grain yield formation was mainly due to the transfer of DM from vegetative organs (Papakosta and Gagianas, 1991; Qi et al., 2020), and the total DM transfer rate could reach 46% (Huo et al., 2021). Other studies have found that the contribution of pre-silking DM is limited (Allison and Watson, 1966; Tollenaar, 1991), and there is little or no DM transfer under modern high-yield conditions (Srivastava et al., 2018; Zhang et al., 2020; Hu et al., 2021; Li et al., 2021). There exists a negative relationship between grain yield and rate of DM transfer from vegetative organs (Yi et al., 2006). More and more studies have shown that post-silking DM contributes much more to final grain yield under high-yield levels (Huang et al., 2007; Meng et al., 2016; Zhou et al., 2016; Liu et al., 2019). For high-yield maize grown under dense planting conditions, higher post-silking DM accumulation reduces DM transfer from vegetative organs, especially the stem, and thus reduces the risk of lodging (Xue et al., 2017). Therefore, for modern high-yield maize cultivation, a high DM transfer rate from vegetative organs may not be essential for yield formation because there is a large amount of DM accumulation during the grain filling stage.
The harvest index (HI) is the proportion of total aboveground DM that is allocated to the kernels. A previous study found that the HI did not change in the U.S. Corn Belt from the 1930s to 1970s while maize grain yield greatly increased (Meghji et al., 1984), as well as the found in Canada (Tollenaar, 1989). However, the HI of maize hybrids released from 1965 to 1993 increased from 0.41 to 0.52 in Argentina (Echarte and Andrade, 2003). In addition, there was also an increase of HI from 0.37 to 0.51 in China (Hou et al., 2012), and an analysis of data from previous studies showed that the HI did not increase when grain yield exceeded 15 Mg ha−1 (Liu et al., 2020a). In our previous study, we showed that an average HI of 0.54 could be achieved for a modern maize hybrid with yield potential of 22.5 Mg ha−1 by using precise field regulation strategies (Liu et al., 2017). Therefore, there is still potential to further improve the HI.
The increase in DM and final grain yield are related to the increase in leaf area (LA) and increased duration of the LA and growth period (Long et al., 2006; Ciampitti et al., 2013; Tian et al., 2020), and there is a significant relationship between grain yield and the duration of grain filling (Daynard et al., 1971; Poneleit and Egli, 1979; Liu et al., 2021a; Rizzo et al., 2022). Because of breeding for increased tolerance to density, the optimal plant density has increased greatly, and cultivars thus have a higher leaf area index (LAI) and increased light interception and use efficiency (Liu et al., 2022b). However, previous studies have shown that a LAI exceeding 5.0 is not necessary for obtaining high grain yield (Stewart et al., 2003; Liu et al., 2015; Liu et al., 2017), and that a LAI of about 5.0–6.0 might be optimal for maize (Li, 2000; Kiniry et al., 2004; Wang et al., 2004; Liu et al., 2020b). A recent meta-analysis showed that the highest maize grain yield was reached when the maximum LAI (MaxLAI) was 6.4 at density of 11.0 plants m−2 and that further increasing MaxLAI would decrease the photosynthetic rate (Hou et al., 2021b). In addition, early leaf senescence adversely affects crop yield during the grain filling stage (Gregersen et al., 2013), and the LAI for high-yield maize should be about 4.0 at maturity (Li, 2000; Liu et al., 2017). Therefore, a reasonable LAI is vital for high yield.
By using precise field regulation strategies, we previously obtained the highest grain yield (25.0 Mg ha−1) in China with a density of 13.5 plants m−2 (Cheng et al., 2021), which was higher than previous studies. The average maize yield was 6.0 Mg ha−1 in China (Liu et al., 2021b) and 5.8 Mg ha−1 in the world (FAO, 2020), which were much lower than our highest yield record. So far, it is not clear in how to achieve yield potential of 25.0 Mg ha−1. Therefore, we performed a synthesis analysis of data from previous studies combined with those from our high-yield experiments to explore how to achieve maize yield breakthrough, from the aspects of DM accumulation and allocation.
Section snippets
Experimental site and design
Five consecutive years’ field experiments from 2017 to 2021 were conducted at Qitai Farm (89°34′ E, 44°12′ N) in Xinjiang, China. A local alternating narrow-wide-row pattern was used with narrow and wide rows of 0.4 m and 0.7 m wide, respectively. We selected six hybrids (SC704, ZD958, XY335, LY66, DH618, and MC670), which once gained highest yield records in China, 16.3, 20.4, 20.8, 21.2, 22.7, and 24.9 Mg ha−1, respectively. In 2017, five of the six cultivars (except MC670) were planted at
Growth duration
Analysis of data from the collected literatures and our field experiments revealed that the duration of the pre-silking (Fig. 2A) and post-silking (Fig. 2B) stages and the whole growth duration (Fig. 2C) significantly increased with increasing grain yield. When analyzing the data from the collected literatures alone, there was no significant correlation between pre-silking duration and grain yield (Fig. 2A, inset); however, the post-silking duration (Fig. 2B, inset) and whole growth duration (
Discussion
Dry matter accumulation and its allocation into the kernels are very important determinants of final grain yield (Rivera-Amado et al., 2019; Liu et al., 2020a). A prolonged growth duration is related to higher DM accumulation and grain yield (Tian et al., 2020). By reviewing data from previous studies combined with data from five consecutive years’ field experiments, we found that the pre-silking, post-silking, and whole growth durations significantly increased as grain yield increased from 1.0
Conclusions
The breeding for erect plant type has increased the density tolerance and improved maize grain yield under dense planting. The breakthrough of grain yield is due to the application of density-tolerant cultivars and precise field regulation strategies without extra resource inputs, which prolongs the post-silking duration and leaf stay-green, reduces the DM transfer from vegetative organs, and increases the DM accumulation and HI. Our innovative findings are of great importance for ensuring food
CRediT authorship contribution statement
Guangzhou Liu: Writing – original draft, Conceptualization, Data curation, Investigation, Writing – review & editing, Visualization. Yunshan Yang: Data curation, Investigation. Xiaoxia Guo: Data curation, Investigation. Wanmao Liu: Data curation, Investigation. Ruizhi Xie: Methodology. Bo Ming: Methodology. Jun Xue: Methodology. Keru Wang: Methodology. Shaokun Li: Methodology, Supervision, Funding acquisition. Peng Hou: Conceptualization, Methodology, Supervision, Funding acquisition.
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
The authors declare the following financial interests/personal relationships which may be considered as potential competing interests:
Acknowledgments
We thank the National Natural Science Foundation of China (32172118; 31871558), the National Key Research and Development Program of China (2016YFD0300110, 2016YFD0300101), National Basic Research Program of China (973, Program 2015CB150401), Basic Scientific Research Fund of Chinese Academy of Agricultural Sciences (S2021ZD05), the Agricultural Science and Technology Innovation Program (CAAS-ZDRW202004), Central Public-interest Scientific Institution Basal Research Fund (No. S2022ZD05).
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