The role of plant labile carbohydrates and nitrogen on wheat-aphid relations 

Abstract

Interactions between plants and herbivores are key drivers of evolution and ecosystem complexity. We investigated the role of plant labile carbohydrates and nitrogen on wheat-aphid relations in a 22 factorial combining [CO2] and nitrogen supply. We measured life history traits (assay 1) and feeding behaviour (assay 2) of bird-cherry oat aphid (Rhopalosiphum padi L.) and English grain aphid (Sitobion avenae F.) forced to feed on single leaf laminae, and reproduction of R. padi in a setting where insects moved freely along the plant (assay 3). Experimental setting impacted aphid traits. Where aphids were constrained to single leaf, high nitrogen reduced their fitness and discouraged phloem feeding. Where aphids could move throughout the plant, high nitrogen enhanced their reproduction. Aphid responses to the interaction between nitrogen and [CO2] varied with experimental setting. The number of R. padi adults varied tenfold with plant growing conditions and correlated negatively with molar concentration of sugars in stem (assay 3). This finding has two implications. First, the common interpretation that high nitrogen favours insect fitness because protein-rich animal bodies have to build from nitrogen-poor plant food needs expanding to account for the conspicuous association between low nitrogen and high concentration of labile carbohydrates in plant, which can cause osmotic stress in aphids. Second, the function of labile carbohydrates buffering grain growth needs expanding to account for the osmotic role of carbohydrates in plant resistance to aphids.

Symmetric response to competition in binary mixtures of cultivars associates with genetic gain in wheat yield

“…However, the response of carbohydrate reserves to neighbour lacked symmetryconcentration of water-soluble carbohydrates increased in Halberd with Scepter neighbour but did not reduce in the same proportion in Scepter with Halberd neighbour. The reason for this lack of symmetry is unknown; it has been speculated that high concentration of water-soluble carbohydrates could play an osmotic role and increase in response to selection for tolerance to aphids (Sadras et al, 2020(Sadras et al, , 2021.…”

Wheat Oxylipins in Response to Aphids, CO2 and Nitrogen Regimes

“…Saturated vs. unsaturated lipid ratios play a crucial role in plant survival and stress tolerance [ 60 ]. In this experimental setting, we found that high levels of CO 2 increased fructose and glucose concentrations, which are essential to buffer the growth requirement of wheat, and play an osmotic role in plant resistance to aphids [ 5 ]. Kanobe et al [ 56 ] concluded that aphids reduced the levels of PUFAs in the leaves and seeds of soybean plants.…”

“…The experimental procedure is fully explained elsewhere [ 5 ]. Briefly, wheat (cv Pedrosa) plants were grown in 9 cm × 9 cm × 10 cm pots with vermiculite (Asfaltex S.A., Barcelona, Spain) in growth chambers.…”

“…Biotic (insects, pathogens, weeds) and abiotic stresses (drought, salinity, extreme temperatures) compromise agricultural production [ 1 , 2 , 3 ]. Elevated [CO 2 ], high temperatures and nitrogen deficiency can also influence the nutritional quality of plants and their secondary metabolite profiles [ 4 , 5 ].…”

“…The bird cherry-oat aphid, Rhopalosiphum padi , and the English grain aphid, Sitobion avenue , are major pests of wheat worldwide. With a focus on this wheat–aphid system, we reported the role of carbohydrates, with an emphasis on osmotic stress, on the fitness and behavior of these insects [ 5 ]. Using the same experimental setting, we investigated whether aphids trigger a defensive reaction from the plant in terms of oxidative stress related to the generation of oxylipins.…”