Resistance and susceptibility in interactions between apple and woolly aphids

Cindayniah Godfrey

If you are interested in contributing samples for this project please email me at Cindayniah.Godfrey@emr.ac.uk for further information.

What I’m doing and what I want. One key objective for this project is to build up a comprehensive survey of WAA genetic diversity across the world. We would appreciate any samples of WAA including, if possible, WAA with a resistance-breaking phenotype which allows them to feed on supposedly resistant rootstocks. We would like the samples to be collected in summer when there is peak WAA abundance.

We will be extracting DNA from the samples and comparing the genetics of different populations. We are especially interested in genetic differences between WAA which are able to feed on supposedly resistance rootstocks and those which cannot. Based on the results of this stage we may carry out some life cycle studies next year using live aphid samples.

We will provide all equipment required to collect and store the samples, as well as detailed instructions to ensure that all samples are collected in a standard way, and a recording sheet. Once your samples have been collected we would ask that you post them back to us.

Background. The woolly apple aphid (WAA; Eriosoma lanigerum) is one of the most important pests of apples in many of the world’s apple-growing regions, able to feed from the roots, trunks, branches and shoots. Woolly apple aphid reproduces asexually, producing up to twenty generations per year and secretes long white waxy filaments to form a protective covering for the colony (Barbagallo et al., 1997). Globally, WAA is one of the most devastating apple orchard pests, particularly in hot climates where severe root infestations frequently compromise tree survival but is currently only a sporadic pest in the UK. Infestations have increased following the recent withdrawal of two effective insecticides (chlorpyrifos and pirimicarb).

WAA resistance in apple. Breeding of WAA resistant rootstocks is increasingly critical for orchard longevity but the molecular mechanisms underpinning resistance are not fully understood. Four sources of WAA resistance from different cultivars have been described as major single genes and tentatively mapped (King et al., 1991; Bus et al., 2000, 2010). Although WAA-resistant rootstocks have been in successful use for several years, WAA with a resistance-breaking phenotype have been observed in Australia (Self, 1966), South Africa (Giliomee et al., 1968), and North Carolina, USA (Rock and Zeiger, 1974). An understanding, therefore, of the mechanism(s) of resistance and the identification of tightly linked markers to allow for gene pyramiding is urgent. The locations of the known WAA resistance genes on different chromosomes make them ideal candidates for gene pyramiding, giving the potential to create rootstocks with durable WAA resistance (Sandanayaka et al., 2003; Bus et al., 2008).

Woolly apple aphid life cycles. There is a lack of knowledge concerning the life cycle and genetic diversity of the pest. Sexual forms are sometimes produced in autumn and sexual females then lay eggs for overwintering. In many parts of the world, including the UK, it has been proposed that the aphids that hatch from these sexually-produced eggs die without feeding (Blackman & Eastop, 2000), and the population may therefore be functionally asexual. The genetic structure of such populations have not been studied, and it is possible that successful sexual reproduction does occasionally occur, as has been recorded elsewhere (e.g. Sandanayaka & Bus, 2005)

Sexual reproduction may lead to rapid emergence of new clones with increased virulence on plants previously considered to be WAA-resistant (Kanvil et al., 2014). A better understanding of WAA life cycle and population genetics is therefore critical to inform plant breeding strategies. NIAB EMR has recently detected the presence of resistance-breaking biotypes of WAA on rootstocks carrying both Er1 and Er2 resistance alleles. This could have serious implications for levels of WAA in UK orchards, making this pest a priority in a warming climate.

References

  1. AHDB (Agriculture and Horticulture Development Board). Not dated. Woolly aphid – additional information. In: AHDB ed. Apple best practice guide. Kenilworth: AHDB.
  2. Barbagallo, S., Cravedi, P., Pasqualini, E., Patti, I., Stroyan, H.L., 1997. Aphids of the principal fruit-bearing crops.
  3. Blackman, R.L., Eastop, V.F., 2000. Aphids on the world’s crops: an identification and information guide. Aphids Worlds Crops Identif. Inf. Guide.
  4. Bus, V., Ranatunga, C., Gardiner, S., Bssett, H., Rikkerink, E., 2000. MARKER ASSISTED SELECTION FOR PEST AND DISEASE RESISTANCE IN THE NEW ZEALAND APPLE BREEDING PROGRAMME. Acta Hortic. 541–547. https://doi.org/10.17660/ActaHortic.2000.538.95
  5. Bus, V.G.M., Chagné, D., Bassett, H.C.M., Bowatte, D., Calenge, F., Celton, J.-M., Durel, C.-E., Malone, M.T., Patocchi, A., Ranatunga, A.C., Rikkerink, E.H.A., Tustin, D.S., Zhou, J., Gardiner, S.E., 2008. Genome mapping of three major resistance genes to woolly apple aphid (Eriosoma lanigerum Hausm.). Tree Genet. Genomes 4, 223–236. https://doi.org/10.1007/s11295-007-0103-3
  6. Bus, V.G.M., Bassett, H.C.M., Bowatte, D., Chagné, D., Ranatunga, C.A., Ulluwishewa, D., Wiedow, C., Gardiner, S.E., 2010. Genome mapping of an apple scab, a powdery mildew and a woolly apple aphid resistance gene from open-pollinated Mildew Immune Selection. Tree Genet. Genomes 6, 477–487. https://doi.org/10.1007/s11295-009-0265-2
  7. Giliomee, J.H., Strydom, D.K., Van Zyl, H.J., 1968. Northern Spy, Merton and Malling-Merton rootstocks susceptible to woolly aphid, Eriosoma lanigerum, in the Western Cape. South Afr. J. Agric. Sci. 11, 183–186.
  8. Kanvil, S., Powell, G., Turnbull, C., 2014. Pea aphid biotype performance on diverse Medicago host genotypes indicates highly specific virulence and resistance functions. Bull. Entomol. Res. 104, 689–701. https://doi.org/10.1017/S0007485314000443
  9. King, G.J., Alston, F.H., Battle, I., Chevreau, E., Gessler, C., Janse, J., Lindhout, P., Manganaris, A.G., Sansavini, S., Schmidt, H., Tobutt, K., 1991. The ‘European Apple Genome Mapping Project’-developing a strategy for mapping genes coding for agronomic characters in tree species. Euphytica 56, 89–94. https://doi.org/10.1007/BF00041748
  10. Rock, G.C., Zeiger, D.C., 1974. Woolly Apple Aphid Infests Malling and Malling-Merton Rootstocks in Propagation Beds in North Carolina. J. Econ. Entomol. 67, 137–138. https://doi.org/10.1093/jee/67.1.137a
  11. Sandanayaka, W.R.M., Bus, V.G.M., 2005. Evidence of sexual reproduction of woolly apple aphid, Eriosoma lanigerum, in New Zealand. J. Insect Sci. 5. https://doi.org/10.1093/jis/5.1.27
  12. Sandanayaka, W.R.M., Bus, V.G.M., Connolly, P., Newcomb, R., 2003. Characteristics associated with Woolly Apple Aphid Eriosoma lanigerum, resistance of three apple rootstocks. Entomol. Exp. Appl. 109, 63–72. https://doi.org/10.1046/j.1570-7458.2003.00095.x
  13. Self, B. F. 1966. Progress in research. Report of East Malling Research Station, 1965, p.1201-1206.

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