The present study identified wheat varieties with strong grass resistance, clarified the physiological mechanism of their anti-grassing effect, and provided a scientific basis for the application of grass-resistant wheat varieties for producing high and stable yield of wheat. Ten wheat varieties commonly used in production were selected to study the effects of Descurainia sophia, Galium tricorne, Wild oat, and sativa extracts on seed germination and seedling growth. Results showed that the Descurainia sophia, Galium tricorne, Wild oat, and Vicia sativa extracts exhibited allelopathic inhibition on wheat seed germination and seedling growth. The allelopathic indices of wheat seed germination rate, seedling height, and root length were −0.12 to −0.19, −0.70 to −0.87, and −0.70 to −0.91, respectively. The weed extract had certain differences in allelopathic inhibition on wheat. The Wild oat extract had the strongest inhibitory effect on seed germination, whereas the Descurainia sophia extract showed the weakest inhibitory effect. The Vicia sativa extract had the strongest inhibitory effect on seedling growth, whereas the Galium tricorne extract showed the weakest inhibitory effect. According to the absolute value of allelopathic index, the effects of the four kinds of weed extracts on seedling growth index were systematically clustered. Results showed that the allelopathic inhibition rate of weed extracts on Wanmai 19 was weak, and the weed resistance was strong. The weed extracts had an allelopathic effect on the root activity and activities of superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT) in the leaves and could promote the content of malondialdehyde (MDA) in the leaves. However, they had minimal allelopathic effect on Wanmai 19. The seedling height and root length of wheat seedlings were significantly correlated with root activity, activities of SOD, POD, and CAT in the leaves and MDA content. Thus, the effect of allelochemicals on the cell membrane in weed extracts could be the cause of inhibited wheat growth.

For gaining insights into the relationship between the accumulation of high-molecular-weight glutenin subunit (HMW-GS) and the distribution of glutenin macropolymer (GMP) in wheat (Triticum aestivum L.), Shannong 12, a cultivar with high glutenin, was used in a field experiment with four phosphorus (P) application levels (0, 40, 100, and 160 kg ha −1 ) under low nitrogen (112.5 kg ha −1 ) and normal nitrogen (225 kg ha −1 ) conditions, respectively. The result showed that HMW-GS in grains formed before 14 d after anthesis, and its content at maturity was higher in P application treatments than in the treatment with no P fertilizer applied. Phosphorus was in favor of the accumulation of HMW-GS under the low nitrogen (N) condition, but caused a negative effect in high P levels under the normal N condition. The content of GMP particle in <10 μm in diameter was significantly reduced with increasing P application. The effect increased with increasing P level under the low N condition, but showed the largest reduction at P level of 100 kg ha −1 and the smallest reduction at P level of 40 kg ha −1 . For GMP particle in 10-100 μm and >100 μm groups, their contents tended to increase with more P applied under both N conditions. Under the normal N condition, there was no significant effect of P level on the number distribution of GMP particle. At maturity, the content of HMW-GS was negatively correlated with the volume of GMP particle in <10 μm group, but positively correlated with that in 10-100 µm group. The result suggested that larger GMP particles have higher HMW-GS content than the smaller GMP particles.