| Two hard bread winter wheat cultivars JN17 and JM20(multiple spike cultivars with high tillering ability, and widely planted in the North China Plain) were grown in field trials in Dongwu Village(35°57’N and 117°3’E, Dawenkou Town, Tai’an City, Shandong province, China) during 2012-2013 and 2013-2014. The main plots were assigned for two contrasting nitrogen fertilisation rates of 0 and 240 kg ha-1, respectively, applied as urea with a basal nitrogen fertilisation rate of 72 kg ha-1, plus a topdressing rate of 168 kg ha-1 at jointing(Feekes stage 6). Subplots were assigned for three plant densities: low(120 plants m-2); normal(180 plants m-2) and high(240 plants m-2). The responses of grain yield, protein size distribution, dough rehological properties and breadmaking quality to plant density under two nitrogen fertilisation rates were investigated. The main results are shown as follows:Significant interactive effects between N level and plant density on the grain yield and quality were observed in the present study. Under 0 kg ha-1 N fertilisation, grain yield, GPC, the concentration of SDS-insoluble glutenins, polymerisation index, wet gluten concentration, dough development time, dough stability time and loaf volume were all decreased with the plant density increasing from 120 to 240 plants m-2 in JN17, while remain constant in JM20. Increasing plant density from 120 to 240 plants m-2 enhanced grain yield, GPC, dough rehological properties and end-use quality under 240 kg ha-1 N fertilisation in both hard bread winter wheat cultivars. Stepwise analysis showed that plant density exerts effects on the dough rheological properties and breadmaking quality of two hard bread winter wheat cultivars under two N levels mainly through changing the polymerisation degree of glutamines in flour. 1. Combined effects of N level and plant density on the grain yield formation in hard bread winter wheatIn the present study, The responses of grain yield to plant density varied between two contrasting N levels. Under 0 kg ha-1 N fertilisation, increasing plant density significantly increase the spikes per unit area at maturity were also increased with the plant density increased from 120 to 240 plants m-2. But kernels per spike were decreased with the increase of plant density. Besides, the thousand kernel weight remained constant among different plant densities. With the increase of plant density, the enhanced spikes per unit area could not be offset by the reduced kernel numbers per spike, lead to adecresed grain yield in JN17. The grain yield was constant among different plant densities in JM20. This was mainly due to the spikes per unit area at maturity. As the decreased kernels per spike were offset by the increased spikes per unit area, the grain yield in JM20 remained constant with the increase of plant density under 0 kg ha-1 N fertilisation.It was observed that with the plant density increasing from 120 to 180 plants m-2, the grain yield was significantly increased, with no further increase with the plant density increasing from 180 to 240 plants m-2 in both cultivars under 240 kg ha-1 N fertilisation. Increasing plant density significantly increased the spikes per unit area at maturity. Increasing plant density from 120 to 180 plants m-2, the percentage increase of spikes per unit area was higher than the percentage decrease of kernels per spike and kernel weight, resulted in and increased grain yield. Further increased of plant density from 120 to 240 plants m-2, significant decrease in kernels per spike and kernel weight resulted in no significant increase in grain yield.According to the obove results, we observed that the responses of grain yield to plant density were significantly influenced by the interactive effect of N level and plant density, and variations were different between two cultivars. 2. Combined effects of N level and plant density on the grain N concentration, grain protein concentratin and composition in hard bread winter wheatIn the present study, the response to the grain protein concentration varied between different N level. Under 0 kg ha-1 N fertilization, increasing plant density significantly decreased the grain N concentration and grain protein concentration of JN17. Variations in grain protein concentration were closely correlated with changes in the amount and composition of protein fractions. With the increase of plant density, the concentration of SDS-insoluble glutenins was decreased significantly, while the concentration of SDS-soluble glutenins was increased, which resulted in a decreased polymerization index. The concentration of glutenins and gliadins were increased with the increase of plant density, but the percentage increase of glutenins were lower than the percentage increase of gliadins, which resulted in a decreased glutenin to gliadin ratio. Different from JN17, the grain N concentration and grain protein concentration were both increased with the increase of plant density. Increased plant density also increased the concentration of SDS-insoluble glutenins, SDS-soluble glutenins, glutenins and gliadins. The percentage increase of SDS-insoluble glutenins and the percentage increase of SDS-soluble glutenins were similar with the increase of plant density, resulted in an constant polymerization index. The percentage increase of glutenins was lower than the percentage increase of gliadins, which resulted in a decreased glutenin to gliadin ratio.Under 240 kg ha–1 N fertilisation in this study, the increased GNC as well as the increased GPC occurred with the increase in plant density. Increased plant density significantly increased the concentration of SDS-insoluble glutenins, SDS-soluble glutenins, glutenins and gliadins, as well as the polymerization index and the glutenin to gliadin ratio. 3. Combined effects of N level and plant density on the quality formation in hard bread winter wheatIn the present study, the dough reological properties and bread-making quality were significantly affected by the interactive effects of N level and pant density. Under 0 kg ha-1 N fertilization, the responses of different variaties to plant density were different. With the increase of plant density, the wet gluten content, water absorption, dough development time, dought stability time and loaf volume were constant among different plant densities, while under 240 kg ha-1 N fertilization, increased plant density significantly increased the gluten wet content, dough development time, dough stability time and loaf volume, and both cultivars showed the same trends. According to the correlation analysis, the dough development time, dought stability time and loaf volume were significantly correlated with the grain protein concentration, the concentrations of SDS-insoluble glutenins and glutenins, as well as the polymerization index, the glutenin to gliadin ratio. However, these quality traits showed no significant relationship with the concentration of SDS-soluble glutenins and gliadins. Stepwise analysis showed that plant density exerted effects on the dough rheological properties and breadmaking quality in both cultivars under two contrasting N levels primarily by changing the polymerisation degree of glutenins in the flour. |
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