Triticum monococcumlines with distinct metabolic phenotypes and phloem-based partial resistance to the bird cherry-oat aphidRhopalosiphum padi

Abstract

Crop protection is an integral part of establishing food security, by protecting the yield potential of crops. Cereal aphids cause yield losses by direct damage and transmission of viruses. Some wild relatives of wheat show resistance to aphids but the mechanisms remain unresolved. In order to elucidate the location of the partial resistance to the bird cherry–oat aphid, Rhopalosiphum padi, in diploid wheat lines of Triticum monococcum, we conducted aphid performance studies using developmental bioassays and electrical penetration graphs, as well as metabolic profiling of partially resistant and susceptible lines. This demonstrated that the partial resistance is related to a delayed effect on the reproduction and development of R. padi. The observed partial resistance is phloem based and is shown by an increase in number of probes before the first phloem ingestion, a higher number and duration of salivation events without subsequent phloem feeding and a shorter time spent phloem feeding on plants with reduced susceptibility. Clear metabolic phenotypes separate partially resistant and susceptible lines, with the former having lower levels of the majority of primary metabolites, including total carbohydrates. A number of compounds were identified as being at different levels in the susceptible and partially resistant lines, with asparagine, octopamine and glycine betaine elevated in less susceptible lines without aphid infestation. In addition, two of those, asparagine and octopamine, as well as threonine, glutamine, succinate, trehalose, glycerol, guanosine and choline increased in response to infestation, accumulating in plant tissue localised close to aphid feeding after 24 h. There was no clear evidence of systemic plant response to aphid infestation.

Unravelling mycorrhiza-induced wheat susceptibility to the English grain aphid Sitobion avenae

“…Metabolites may also play a role in resistance; Greenslade et al 22. showed distinct metabolic phenotypes for resistant T. monococcum lines in comparison to susceptible lines.…”

“…showed distinct metabolic phenotypes for resistant T. monococcum lines in comparison to susceptible lines. The expression of trehalose was shown to be elevated in T. monococcum MDR049 and MDR657 and T. aestivum Solstice after aphid infestation22. The disaccharide sugar trehalose has been shown to increase plant resistance to the Powdery mildew pathogen ( Blumeria graminis ) by accelerating the stress signalling response48.…”

“…These lines were identified in previous work to have varying levels of susceptibility to R. padi 22. We determined whether mycorrhizal colonisation can affect the resistance and susceptibility that diploid T. monococcum varieties, and T. aestivum , hold towards S. avenae , through fecundity and development studies using whole plant cages.…”

The price of protection: a defensive endosymbiont impairs nymph growth in the bird cherry‐oat aphid, Rhopalosiphum padi

“…3C), in line with our original prediction. The mechanism of aphid resistance in HsP5 has not been fully characterized, but partial resistance to aphids in the wild relative of wheat, Triticum monococccum, is thought to be phloemmediated, linked to increased secondary metabolite concentrations (Greenslade et al, 2016). Whatever the causal mechanism of resistance, it is possible that the decrease in nymph growth rate on HsP5 in aphid lines harboring H. defensa resulted from resource demand by the endosymbiont, which intensified the negative effects of feeding on a poor quality plant host.…”

Searching for wheat resistance to aphids and wheat bulb fly in the historical Watkins and Gediflux wheat collections

“…Due to differences in rate of development (Greenslade et al , 2016), the timings of bioassays differ by 1 day between the two aphid species, with S. avenae alates put onto plants on day 8 and R. padi alates on day 9 after sowing. On day 10 after sowing, 24 h ( R. padi ) and 48 h ( S. avenae ) from when the alates were put onto the wheat, they were removed with fine forceps, the number of nymphs produced recorded and the clip cages replaced.…”