We measured the effect of wheat density on weed biomass and seed production, wheat biomass, and grain yield in five wheat cultivars in Pakistan in the presence and absence of individuals of the weed Medicago polymorpha L. The presence of M. polymorpha decreased wheat biomass and grain yield by up to 25%, even though the density of the weed was low (5 plants m⁻²). When wheat density was increased from 130 to 390 plants m⁻², weed biomass and seed production were reduced by 68 and 85%, respectively, across all five cultivars. The average wheat yield increased by up to 7% with increasing density for all wheat cultivars. The cultivars varied in their responses to the weed and to their own density. While most effects were additive, there was a highly significant interaction between wheat density and cultivar on weed seed production, in which the cultivar that completely suppressed weed seed production at high wheat density was among the least suppressive at low density. The cultivar that produced the highest yield across all treatments was not among the best at suppressing the weed or producing biomass, suggesting that tolerance of weed biomass is also important at low but still damaging levels of weed infestation. Our results confirm that even a relatively low density of M. polymorpha can incur significant yield losses, but also show that it can be managed effectively with cultural practices like increasing seed rate and by selecting weed suppressive and tolerant cultivars suited to the local environment.

中文翻译：

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案例研究：小麦密度和品种对毛刺（Medicago polymorpha L.）生长繁殖、小麦生长和产量的影响

我们在存在和不存在杂草Medicago polymorpha L个体的情况下测量了小麦密度对巴基斯坦五个小麦品种的杂草生物量和种子产量、小麦生物量和谷物产量的影响。M. polymorpha的存在降低了小麦生物量和即使杂草的密度很低（5 株 m ^-2），谷物产量也提高了 25%。当小麦密度从 130 株增加到 390 株时 m ^-2，所有五个品种的杂草生物量和种子产量分别减少了 68% 和 85%。随着所有小麦品种密度的增加，平均小麦产量增加了 7%。品种对杂草和自身密度的反应各不相同。虽然大多数影响是相加的，但小麦密度和品种之间对杂草种子生产存在高度显着的相互作用，其中在高小麦密度下完全抑制杂草种子生产的品种在低密度时抑制作用最小。在所有处理中产生最高产量的品种在抑制杂草或产生生物量方面并不是最好的品种，这表明杂草生物量的耐受性在杂草侵染程度低但仍具有破坏性的情况下也很重要。M. polymorpha会导致显着的产量损失，但也表明可以通过提高播种率和选择适合当地环境的杂草抑制和耐受品种等文化实践对其进行有效管理。