Objective 7 - Lesley Smart (RRes)

Insect resistance in wheat: Cereal aphids (RRes)

Final Report (pdf) PDF


The grain aphid, Sitobion avenae, and the bird-cherry oat aphid, Rhopalosiphum padi are major pests of wheat, vectoring virulent strains of Barley Yellow Dwarf Virus (BYDV), one of the most damaging cereal viruses in the world. In addition, feeding aphids intercept nitrogen assimilates necessary for developing grain, resulting in significant yield losses and affecting the quality of bread making wheat. Seed treatment with the systemic insecticide imidacloprid can protect the crop during early growth stages, but an additional application of a pyrethroid insecticide may be necessary to control secondary spread from initial colonies. Breeding of resistant varieties has been particularly important in the management of other species of aphids attacking wheat worldwide e.g. the greenbug, Schizaphis graminum, and the Russian wheat aphid, Diuraphis noxia (Berzonsky et al. 2003). However, despite considerable research effort, to date there are currently no commercial wheat varieties resistant to UK resident aphid species, although resistance to S. avenae has been found in Triticum monococcum (Migui & Lamb 2004). The unique resources available through the WGIN project provide a great opportunity for further targeted research on suitable traits for resistance to UK cereal aphid species. Increasingly stringent regulatory requirements and high costs for registration of insecticides have, and will continue to, limit the number of such products available to growers. In addition, impetus for finding alternative control methods to insecticides has come from the public perception of health or environmental issues associated with insecticide use. In line with Defra’s strategic objectives towards sustainable crop production and a healthy natural environment, the development of insect resistant wheat varieties is a grower-friendly insect pest management solution and will make a substantial contribution towards reducing insecticide use.

Activity 1: To explore whether the differential response of hexaploid wheats to two different cereal aphid species has a genetic basis

Approaches and Research Plan

An initial investigation, under BBSRC funding, of a very limited number of lines from the Spark x Rialto mapping population that show selective response to D. noxia and S. graminum, has demonstrated differential attraction for R. padi and S. avenae. The sole aim of this work is to determine whether this trait is under simple mendelian control and therefore is potentially exploitable by the wheat breeders. By also exploring the response of F1 plants, it will be possible to determine whether the trait is dominant or recessive. Initially, selected lines in the mapping population, showing either strong resistance or susceptibility to D. noxia and S. graminum, will be tested against R. padi and S. avenae in laboratory bioassays. If successful, this data set will be used to apply for additional research funds from defra through LINK or via application for some of the WGIN sub-contractor funds. In addition, if a genetic analysis is published by others, the current UK germplasm will be explored for the existence of this QTL and all material will be tested in the aphid bioassays to see if there is a correlation between the QTL and all resistance genotypes identified.

Activity 2: To determine the differential susceptibility to two cereal aphid species of targeted lines from the Spark x Rialto mapping population


This will involve the use of No-choice bioassays, since this method provides the most stringent conditions, in that aphids that do not settle will die. Each wheat line will be tested against the two major cereal aphid species R. padi and S. avenae, both of which are reared in laboratory cultures under controlled environmental conditions (16:8h L:D and 22°C+/-2°C). In replicated trials under the same controlled conditions, a single plant at the two leaf growth stage will be placed in each of ten glass chimney cages and 5 or 10 alates aphids, depending on the species being tested, will be introduced into each cage. (R. padi produce large numbers of nymphs in a 24 h period, but S. avenae are less prolific). Settlement of alatae will be assessed after 2, 5 and 24 h and nymph production at 24 h after which the alates will be removed. To determine effects on aphid nymph survival, the plants will be kept for a further 3 days after which the remaining nymphs will be counted. This work will test initially the extent to which the natural genetic variation in the lines can influence aphid colonisation and provide a “settling index”. If lines with differential settlement and/or nymph survival are identified, then more detailed tests will be conducted to determine development such as mean relative growth rates (MRGR). In these trials, neonate nymphs produced on the test lines will be weighed on a Cahn microbalance in batches of 5 then caged on a plant of the same line. After 5 days the surviving nymphs will be re-weighed and the MRGR will be calculated (MRGR = (ln 5 day wt – ln birth wt) /5) (Wyatt and White, 1977). This test will assess the possible effects of test lines on the rate of the aphid species development. The experimental designs and subsequent analysis will be decided in consultation with a Consultant Statistician from the Biomathematics and Bioinformatics Department. Experience in the design and analysis of similar experiments in previous projects will influence the experiments in this project. If lines with enhanced resistance to one or more aphid species are identified, these will enter into near- isogenic line production at JIC (activity 2) so that further analysis of the phenotype can take place at a later date.

Berzonsky, W.A., Ding, H., Haley, S.D., Lamb, R.J., McKenzie, R.I.H., Ohm, H.W., Patterson, F.L., Peairs, F.B., Porter, D.R., Ratcliffe, R.H., and Shanower, T.G. (2003) Breeding wheat for resistance to insects. Plant Breeding Reviews, 22: 221–296.
Migui, S.M. and Lamb, R.J. (2004) Seedling and adult plant resistance to Sitobion avenae (Hemiptera : Aphididae) in Triticum monococcum (Poaceae), an ancestor of wheat. Bulletin of Entomological Research, 94, 35-46.
Wyatt IJ and White PF, Simple estimation of intrinsic increase rates for aphids and tetranychid mites. J Applied Ecology 14:757-766 (1977).

This Page Was Last Edited: 16-Dec-2011