Contribution of Proximal and Distal Grains Within Spikelets in Relation to Yield and Yield Components in the Winter Wheat Production Region of China From 1948 to 2012

Abstract

Grain number and weight within a spikelet are major yield components which determine the grain yield in wheat. The objective of this study was to explore genetic gains in grain performance within wheat spikelets at the individual grain level and its effect on grain yield and evaluate genetic progress in stem internode length and other yield-related traits. We conducted field experiments across three growing seasons in the western Yellow and Huai Valley of China; incorporating 17 bread wheat cultivars released from 1948 to 2012. Yields were significantly correlated with year of release. Yield gains equated to 3.95 g m−2 yr−1 in response to increases in total grain weight per m2 (GW) in proximal (G1 and G2) and distal (G3 and G4) grains, despite a decline in the proportional contribution of proximal grains to yield and increase in the proportional contribution of distal grains to yield with year of release. Grain number per m2 (GN), thousand-grain weight (TGW), and harvest index (HI) increased with year of release, but plant height decreased. Both grain number per spikelet of proximal and distal grain contributed to the increase in total GN. However, the contribution ratio of GN in proximal grains to total GN declined, and the proportion in distal grains increased. Average single grain weight (SGW) increased linearly at G1, G2, G3, and G4 with year of release and contributed to the increase in TGW. The G3 and G4 grain positions had much lower individual grain weights but increased at a faster rate than G1 and G2. At G1, G2, and G3 grain positions, from bottom to top spikelets, the newly released cultivars had the heaviest grains and the old cultivars had the lightest grains. New cultivars had more spikelets than old cultivars and the number of grains (proximal and distal grains) in the apical spike increased with year of release. The length of five internodes decreased significantly with year of release, more so in the upper than lower internodes, all of which contributed to the decline in plant height. In summary, increasing the number and weight of distal grains could increase grain yield, TGW, and GN.

Physiological bases of cultivar differences in average grain weight in wheat: Scaling down from plot to individual grain in elite material

“…Both the processes described above, would lead to a higher proportion of small grains and so will be referred to below as 'populational' effects. The important roles of these populational effects on the trade-off between GNM2 and AGW is supported by a large number of studies (Acreche and Slafer, 2006;Chen et al, 2019;Feng et al, 2019;Ferrante et al, 2017;García et al, 2013;Li et al, 2016;Miralles and Slafer, 1995b;Quintero et al, 2018).…”

“…Most studies comparing wheat cultivars and showing differences in grain number and AGW have focused on the dichotomy between old cultivars and new ones, or between tall cultivars and semi-dwarf ones (Chen et al, 2019;Ferrante et al, 2017;Miralles and Slafer, 1995b), or they have explored cultivars showing wide-ranging yield potentials (e.g., Peltonen-Sainio et al, 2007;Quintero et al, 2018). All these studies, together with an abundance of studies that have focused on yield responses to different management practices (e.g., Acreche and Slafer, 2006;Feng et al, 2019;Fischer, 1993;Li et al, 2016) have concluded that yield variations are mainly related to variations in GNM2 (e.g., Slafer et al, 2014 and references therein). Given the negative relationship that commonly exists between GNM2 and AGW (Slafer et al, 2014;Slafer and Savin, 1994), studies that rely on a high variability in GNM2, only highlight the dominant effect of GNM2 on AGW.…”

“…The second populational effect suggested in the literature having a putative effect on AGW, operates at the within-spike level. From this point of view, increasing grain number per m 2 through an increase in NGS is accompanied by a higher proportion of small grains positioned in basal or apical spikelets within the spike (e.g., Feng et al, 2019;Ferrante et al, 2017;Miralles and Slafer, 1995a). It is well established that, within spikelets, the grains in distal florets are smaller than in basal florets (e.g., Baillot et al, 2018;Miralles and Slafer, 1995a;Rawson and Evans, 1970).…”

“…The idea of a trade-off originating from sink limitation, is based on the observation that an increase in GNM2 usually leads to a higher proportion of grains of low potential weight (Acreche and Slafer, 2006;Chen et al, 2019;Feng et al, 2019). The higher proportion of small grains could be driven by processes occurring at two different levels.…”

Winter Wheat Adaptation to Climate Change in Turkey

“…Under normal conditions, the grain formation rate per average per spikelet of the wheat spike is around 2.7, and it is well known that the sterility rate in the third florets of the wheat spike is about 30% [61]. One of the most important reasons why the WW genotypes tested had low GY was sterility in the spike (SS).…”