Impacts of domestication on the rhizobial mutualism of five legumes across a gradient of nitrogen-fertilisation

Aims Domestication and crop breeding has improved plants for human use, but may have unintended consequences for traits that are not selected upon. Disruption in the mycorrhizal mutualism has been observed in crops; possibly due to breeding in fertilised soil. Little is known about whether the legume-rhizobia mutualism can be disrupted by domestication and crop evolution, despite the importance of symbiotic nitrogen fixation. We aimed to identify differences in mutualistic outcomes between five legume cultivars and their wild progenitors in terms of their reactions across varying nitrogen levels. Methods With five greenhouse experiments, we characterised symbiosis traits in chickpea, lentil, pea, peanut, and soybean across a gradient of N fertilisation to characterise whether symbiosis traits differ context specifically between wild and domesticated lines. Results At lower levels of N addition, wild soybean benefited more from rhizobia than domesticated soybean. Chickpea cultivars abandoned symbiosis at lower N than wild chickpea accessions. Chickpea cultivars reduced per-nodule colony forming units (CFU) in response to N addition more than wild chickpeas, but lentil cultivars reduced CFU less than lentil accessions. The lentil, pea, and peanut cultivars did not differ from their wild relatives in rhizobial benefit, nor in nodulation response to N addition. Conclusions Differences in the regulation of the root nodule symbiosis are evident between domesticated and wild chickpea and soybean, but not lentil, pea, or peanut. This indicates that mutualism disruption—a decrease in the magnitude of the mutually symbiotic interaction—is a possible, but not necessary, consequence of domestication.