Abstract
Genetic improvements have significantly contributed to wheat production. Five wheat cultivars—widely grown in north China in the 1950s, 1990s, or 2010s—were grown in field experiments conducted in the 2014–2015 and 2015–2016 growing seasons. This study evaluated the genetic progress in wheat grain yield and its related traits in north China and explored how breeding and selection have influenced grain numbers and weights within spikelets in the past 60 years. The results showed that the significant increases in grain yield in the past 60 years were mainly due to increases in grain number per spike and grain weight, while spike number per m2 has not changed significantly. Improvements in thousand grain weight (TGW) from the 1950s to 2010s have occurred at four grain positions (G1 to G4). The relative contribution of G4 to TGW increased over time, but was much less than the contributions of G1, G2, and G3. Indeed, the average grain weight at G4 was much less than that of 1000 grains. The increase in grain number per spike since the 1950s was mainly due to an increase in grain number at G1, G2 and G3, with the relative contribution of grain position to grain number being G1 > G2 > G3 > G4. Dwarfing genes increased grain number per spike and grain number at G3 and G4, but not TGW. In future, yields could be boosted by enhancing grain weight at G4 and grain number at G3 and G4, while maintaining those at G1 and G2.
Highlights
Wheat is an important crop throughout the world (Morgounov et al, 2010; Manès et al, 2012; Beche et al, 2014)
We found no apparent change in spike number per m2, which agrees with the findings of Zheng et al (2011) and Zhang et al (2016) in the Henan Province, but disagrees with those of Zhou et al FIGURE 6 | Average grain weight (A), grain number (B), and total grain weight (C) at each grain position in five wheat cultivars released in different decades and grown in 2014–2015 and 2015–2016
Our results showed that grain number, average grain weight, and total grain weight from the bottom to the top spikelets showed parabolic changes, indicating that the middle spikelets had a significant advantage for priority development than the bottom and top spikelets, which agrees with previous studies (He et al, 2000; Guo and Schnurbusch, 2015; Li Y. et al, 2016)
Summary
Wheat is an important crop throughout the world (Morgounov et al, 2010; Manès et al, 2012; Beche et al, 2014). There have been significant genetic improvements in wheat yields in the past decades (Siddique et al, 1989a,b; Zhou et al, 2007a; Xiao et al, 2012; Sun et al, 2014). Most studies have attributed the increased wheat yields in past decades to increases in grain number per spike (Siddique et al, 1989a), thousand grain weight (TGW), or both (Donmez et al, 2001; Zhou et al, 2007a; Zheng et al, 2011; Xiao et al, 2012; Zhang et al, 2016). Few studies have paid attention to changes in TGW and grain number per spike at different grain positions
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