Disentangling the effects of PAR and R : FR on lodging-associated characters of wheat (Triticum aestivum)

It has been previously demonstrated that large wheat canopies are more prone to lodging than smaller canopies and it has been suggested that this is because of the plant's response to changes in the light environment. However, it is unclear whether plants are responding to reduced light quantity (photosynthetically active radiation, PAR) or reduced light quality (red:far-red, R:FR). Two glasshouse experiments were designed, using shading materials and supplementary light, to manipulate PAR and R:FR independently, so that the response of lodging-associated characters of wheat could be ascribed to the different aspects of shade. The increase in lodging susceptibility associated with mutual plant shading was found to be because of both PAR and R:FR. Calculated stem failure wind speed and its component traits responded to shading entirely through their response to reductions in PAR. Ear number, which led to differences in plant leverage, was also explained by differences in PAR. In contrast, calculated anchorage failure wind speed and rooting traits demonstrated additional responses to R:FR, over and above those to PAR. Thus, the aspect of mutual plant shading responsible for increased lodging susceptibility of wheat varied between stem and root traits. PAR was solely responsible for changes in stem traits associated with lodging but R:FR played a role in determining rooting traits that affect the anchorage capacity of wheat plants.