Population size plays a crucial role in determining wheat yields. Altered carbohydrate accumulation resulting from increased competition between populations and individuals leads to poor-quality stems. The sowing date can mitigate competition in densely planted populations. However, the underlying mechanism by which it confers resistance to wheat lodging remains elusive. In this study, Zimai 28 (lodging-sensitive variety) and Shannong 28 (lodging-resistant variety) were used with three sowing treatments on October 22 (S1), October 28 (S2), and November 3 (S3). The sowing rate was adjusted to ensure adequate population size and consistency in the overwintering populations across sowing dates (300 plant m⁻² for S1, 375 plant m⁻² for S2, and 525 plant m⁻² for S3). The lodging resistance in winter wheat was increased by delayed sowing and increased sowing rate, which led to a reduction in tiller numbers and fostered primary stem development. A reduction in the overwinter cumulative temperature from 500 to 450 °C, coupled with an elevation in sowing rates from 300 to 375 plant m⁻² (transition from S1 to S2), corresponded with a notable increase in structural carbohydrates (lignin, cellulose, hemicellulose, and pectin) by 175.07 mg g⁻¹. Additionally, there was a moderate increase in non-structural carbohydrates, including soluble sugars and starch, by 15.54 mg g⁻¹. Delayed sowing and increased sowing rate elevated the precursor contents of lignin synthesis. Enhanced metabolic activity of related pathways ultimately increased dimer/trimer content. In summary, this study highlights the pivotal role of lignin metabolites and cross-linked structures in determining the stem stiffness breaking strength.

Drought at the grain filling stage of wheat will cause premature leaf senescence, thus leading to considerable loss of wheat yield. Therefore, this paper aims to establish a cultivation technology for strong drought resistance, delayed senescence, and yield improvement based on the analysis of hormones homeostasis obtained by applying chemical control substances. Experiments were conducted with two genotypes of wheat. Four water irrigation treatments were applied to impose the water deficit, including well-watered control treatment (WW), mild water deficit (MiWD), moderate water deficit (MoWD), and severe water deficit (SWD). Exogenous abscisic acid (ABA) was sprayed on the plants at the anthesis stage of the wheat. As a result, exogenous ABA reduced initial senescence rate (r₀), total duration of chlorophyll (Chl_total), rapid senescence phase (Chl_loss), and the accumulated temperature at an inflection point (M) but improved the persistence phase (Chl_per) of flag leaves under all of the four treatments. However, exogenous ABA produced inconsistent effects on photoassimilate relocation and grain weight under different treatments. It produced positive regulatory effects on grain weight under WW, MiWD, and MoWD treatments. On the one hand, spraying ABA during the persistence phase of flag leaves reduced the ratios of zeatin to gibberellin (Z/GA₃), spermine to spermidine (Spm/Spd), and salicylic acid to ABA (SA/ABA), which prolonged active photosynthesis by stimulating high level of proline (Pro) and increased the activities of antioxidant enzymes, such as superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), and ascorbate peroxidase (APX). Therefore, drought tolerance was enhanced, and more photosynthetic assimilates were accumulated. On the other hand, the rapid senescence phase and the transport rate of assimilates into grains were accelerated, resulting in higher grain weight, yield, and water use efficiency (WUE). However, under SWD treatment, exogenous ABA improved the ratio of SA/ABA, leading to low Pro content and low antioxidant enzyme activity of flag leaves in the rapid loss phase. Meanwhile, drought resistance declined and the transport duration of assimilates into grains was shortened, thus making photosynthetic assimilates redundant. Therefore, exogenous ABA can lead to the reduction in grain weight, yield, and WUE of wheat under SWD treatment.

Premature senescence after anthesis reduces crop yields. Delaying leaf senescence could maintain photosynthetic activity for a longer period and lead to a higher photosynthetic rate. Recent studies have provided some insights into the interaction between cytokinin and nitrogen (N) in the regulation of plant development. In the present study, foliar application of exogenous 6-benzylaminopurine (6-BA) and lovastatin, an inhibitor of cytokinin synthesis, was combined with three N rates [0 kg ha⁻¹ (low nitrogen, LN), 240 kg ha⁻¹ (normal nitrogen, NN), and 360 kg ha⁻¹ (high nitrogen, HN)] in two wheat cultivars, Wennong 6 (with a staygreen phenotype) and Jimai 20 (with a non-staygreen phenotype). Flag leaf senescence was assessed using a Gompertz growth curve. Grain mass, dry matter accumulation and distribution, total N of flag leaf, and concentrations of zeatin riboside (ZR) and abscisic acid (ABA) were also used to evaluate the functional characteristics of flag leaves. Grain mass was negatively correlated with initial senescence rate (r₀) and duration of rapid chlorophyll loss (Chl_loss), whereas it was positively correlated with maximum senescence rate (r_max), average senescence rate (r_aver), persistence phase (Chl_per), total duration of flag leaf (Chl_total) and inflection point cumulative temperature (M). Compared to Jimai 20, Wennong 6 had larger r_aver, Chl_per, and Chl_total. The concentration of ZR was highest under the 6-BA × NN treatment, followed by the 6-BA × HN and 6-BA × LN treatments. However, the concentration of ABA showed the opposite trend. It was concluded that the staygreen phenotype Wennong 6 was associated with greater grain mass and altered cytokinin metabolism and could be classified as a functional staygreen type. Foliar application of 6-BA interacting with N at the NN level (240 kg ha⁻¹) may be a beneficial strategy for improving grain yield of wheat by regulating endogenous hormones and the flag leaf senescence process. Increasing endogenous cytokinin promoted the transport of dry matter to grain.