Preferential helping to relatives: A potential mechanism responsible for lower yield of crop variety mixtures?

Abstract

Variety mixtures, the cultivation of different genotypes within a field, have been proposed as a way to increase within‐crop diversity, allowing the development of more sustainable agricultural systems with reduced environmental costs. Although mixtures have often been shown to over‐yield the average of component varieties in pure stands, decreased yields in mixtures have also been documented. Kin selection may explain such pattern, whenever plants direct helping behaviors preferentially toward relatives and thus experience stronger competition when grown with less related neighbors, lowering seed production of mixtures. Using varieties of durum wheat originating from traditional Moroccan agrosystems, we designed a greenhouse experiment to address whether plants reduced competition for light by limiting stem elongation when growing with kin and whether such phenotypic response resulted in higher yield of kin groups. Seeds were sown in groups of siblings and nonkin, each group containing a focal plant surrounded by four neighbors. At the group level, mean plant height and yield did not depend upon relatedness among competing plants. At the individual level, plant height was not affected by genetic relatedness to neighbors, after accounting for direct genetic effects that might induce among‐genotype differences in the ability to capture resources that do not depend on relatedness. Moreover, in contrast to our predictions, shorter plants had lower inclusive fitness. Phenotypic plasticity in height was very limited in response to neighbor genotypes. This suggests that human selection in crops may have attenuated shade‐avoidance responses to competition for light. Future research on preferential helping to relatives in crops might thus target social traits that drive competition for other resources than light. Overall, our study illustrates the relevance of tackling agricultural issues from an evolutionary standpoint and calls for extending such approaches to a larger set of crop species.

Shift in beneficial interactions during crop evolution

“…Kin recognition implies that plants display phenotypic plasticity toward reduced competition for resources when growing with kin, leading to increased fitness in kin groups. Preferential helping to relatives might hamper the efficiency of varietal mixtures (Fréville et al, 2019 ), an advocated practice for mobilizing mechanisms such as niche partitioning and facilitation that may drive positive biodiversity effects on productivity. Convincing evidence of kin recognition is still rare in wild species (Karban et al, 2013 ; Pennisi, 2019 ) and in crops.…”

“…Convincing evidence of kin recognition is still rare in wild species (Karban et al, 2013 ; Pennisi, 2019 ) and in crops. Although crops can indeed display phenotypic plasticity in response to relatedness in cultivated plants (Fang et al, 2013 ; Murphy, Swanton, et al, 2017 ; Murphy, Van Acker, et al, 2017 ; Zhang, Zhang, et al, 2016 ; Zhang, Liu, et al, 2016 ), how such plastic response affects fitness remains to be more thoroughly explored, by paying special attention to other confounding effects such as those arising from differences in competitive ability among genotypes (Fréville et al, 2019 ; Masclaux et al, 2010 ). Assessing whether interactions mediated by kin recognition might have shifted during domestication and breeding needs further work.…”

Detect thy family: Mechanisms, ecology and agricultural aspects of kin recognition in plants

“…As kin selection can lead to more cooperative traits in plants and greater group performance, its potential use in crop breeding could be considered (Murphy, Swanton, et al, 2017). Kin discrimination has been demonstrated in several crop species, for example, soybean (Murphy, Van Acker, et al, 2017), barley (Ninkovic, 2003), sorghum (Zhang et al, 2016), wheat (Zhu & Zhang, 2013, but see Fréville et al, 2019), rice (Yang et al, 2018) and Jerusalem artichoke ( Helianthus tuberosus , Fukano, Guo, Noshita, Hashida, & Kamikawa, 2019), with findings that kin‐interacting plants tend to exhibit more cooperative root systems. A question then arises: to what would extent crop selection for kin recognition and discrimination be an effective means to increase crop yields?…”

Effects of kin recognition on root traits of wheat germplasm over 100 years of breeding

“…Recent studies have assessed kin response based on pot experiments, allowing simultaneous interaction (e.g. Fréville et al 2019). This can be problematic as it is not possible to distinguish the effects of the indirect kin recognition from effects of more direct interaction such as competition for limited resources.…”