Genetic diversity of root-infesting woolly apple aphid Eriosoma lanigerum (Hausmann) (Hemiptera: Aphididae) populations in the Western Cape

[摘要] ENGLISH ABSTRACT:Characterizing the genetic structure of a pest population can provide an understanding of the factorsinfluencing its evolution and assist in its ultimate control. The aim of the present study was to characterizethe genetic structure of woolly apple aphid Eriosoma lanigerum (Hausmann) populations in the WesternCape Province in South Africa. Since this economically important apple pest has not previously beencharacterized at molecular level, it was necessary to evaluate methods for determining the genetic structureof E. lanigerum populations. Two different molecular techniques were evaluated viz. random amplificationof polymorphic DNA (RAPD) and amplified fragment length polymorphism (AFLP). This study representsthe first application of the latter technique to members of the Aphididae.Aphids were sampled from four regions in the Western Cape in South Africa viz. Elgin, Ceres, Vyeboom andVilliersdorp. A spatially nested sampling design was used to establish the distribution of the geneticvariance of aphids. A total of 192 individuals from 13 farms were analysed. Ten RAPD primers werechosen for analysis from an initial assay of 25 after fragment reproducibility had been confirmed. For AFLPanalysis three different rare-cutting restriction enzymes were evaluated for AFLP analysis, viz. EcoRI, SseIand MluI. The latter yielded the best results in combination with the frequent-cutting enzyme MseI.Twenty-five AFLP selective primer pairs were evaluated, out of which five were chosen for analysis of thetotal population.Two hundred and fifty AFLP fragments and 47 RAPD fragments were scored for analysis. Both analysesindicated that a low level of genetic variation was apparent in E. lanigerum populations and that nodifferentiation resulted from geographic isolation. From RAPD analyses it was deduced that all variationcould be attributed to differences between individuals. AFLP analysis indicated that, whereas geneticdifferences in E. lanigerum populations between orchards were negligible, a significant portion of geneticvariation could be attributed to differences between farms and individuals within farms.Therefore, AFLP analysis allowed for finer discrimination of the genetic structure of E. lanigerumpopulations than RAPD analysis and is recommended for studies of other aphid species. The fact that mostof the genetic variation present in E. lanigerum populations could be found on small spatial scales indicatedthat sampling individuals over a wide geographic area was an ineffective way of detecting the geneticdiversity present in E. lanigerum populations. The low level of variation in populations is most likely due tothe exclusive occurrence of parthenogenetic reproduction, founder effects (including distribution of infestedplant material from a limited source) and selective factors such as the use of resistant rootstocks orpesticides. Furthermore, the low level of variation found indicated that the possibility of controlling E.lanigerum in the Western Cape using host plant resistance is favourable. Thus, plant breeders developing resistance to E. lanigerum can expect plant entries to be exposed to most of the genetic diversity present inWestern Cape populations, regardless of location.

[发布机构] Stellenbosch University