Des pite the growing concerns over the damages and unsustainability of conventional agriculture, arable farmers struggle to convert to organic cropping practices. In wheat farming, the lack of cultivars adapted to organic cropping has prompted a search for alternatives to better cope with unpredictability and stress. In that respect, heterogeneous material (HM) has attracted a lot of attention for its good performances and yield stability across years and environments. These benefits are thought to arise from facilitative plant interactions brought forth by intraspecific diversity, but much remains to be known about the mechanisms at play as well as their interactions with the other elements of the cropping system. Here, we review the literature on plant interactions within organic bread wheat crops through the successive scopes of (i) heterogeneous material, (ii) plant density, and (iii) their interaction. Our major findings are as follows: (1) optimizing heterogeneous material performance and evolutionary trajectories grossly amounts to tipping the balance between competitive and facilitative plant interactions toward the latter. (2) The stress gradient hypothesis applies to the competition/facilitation balance within HM: The more stressful the conditions, the more facilitation happens. (3) Plant density also affects this balance, and the relationship between net facilitation and plant density in HM follows a humped curve. (4) Therefore, the optimal plant density range for HM should be both narrower and lower than for pure lines, and also harder to predict. (5) High-tillering, high individual yielding plant types should probably be aimed for in HM, for two reasons: first, they perform better at the lower-than-the-recommendations plant densities at which HM are expected to best express their potential. Second, optimal plant densities of such plant types are more stable across environments, which should increase the probability of falling within the narrower optimal plant density range of HM, particularly in unpredictable and/or stressed environments.

尽管人们越来越担心传统农业的破坏性和不可持续性，但耕地农民仍在努力转向有机种植方式。在小麦种植中，缺乏适合有机种植的品种促使人们寻找替代品以更好地应对不可预测性和压力。在这方面，异质材料（HM）因其在多年和环境中的良好性能和产量稳定性而引起了广泛关注。这些好处被认为是由种内多样性带来的促进植物相互作用产生的，但关于起作用的机制以及它们与种植系统其他元素的相互作用仍有许多待了解。这里，我们通过（i）异质材料，（ii）植物密度和（iii）它们的相互作用的连续范围回顾了有关有机面包小麦作物中植物相互作用的文献。我们的主要发现如下：（1）优化异质材料性能和进化轨迹在很大程度上意味着将竞争性和促进性植物相互作用之间的平衡向后者倾斜。(2) 压力梯度假设适用于 HM 内部的竞争/促进平衡：条件越紧张，促进发生的越多。(3)植物密度也影响这种平衡，HM中净促进与植物密度之间的关系呈驼峰曲线。(4) 因此，HM 的最佳植物密度范围应该比纯系更窄和更低，也更难预测。(5) 高分蘖、高单产的植物类型可能应该针对 HM，原因有两个：首先，它们在低于建议的植物密度下表现更好，而 HM 预计在该密度下最能发挥其潜力. 其次，此类植物类型的最佳植物密度在整个环境中更加稳定，这应该会增加落入 HM 较窄的最佳植物密度范围的可能性，特别是在不可预测和/或压力大的环境中。