Identification of molecular markers linked to woolly apple aphid (Eriosoma lanigerum) (Hausmann) resistance in apple

[摘要] ENGLISH ABSTRACT:Apple (Malus x domestica Borkh.) is an important horticultural crop worldwide and in the WesternCape. The income generated from apple and other deciduous fruit production amounts toapproximately 25% of the gross total value of horticultural production in the Western Cape.Unfortunately diseases and pests adversely affect fruit production in this region.Woolly apple aphids (Eriosoma lanigerum L. (Hausmann» have a significant effect on the appleindustry in the Western Cape. Damage caused is two-fold, occurring aerially and terrestrially. Insectscolonise the plants, feeding off the phloem sap. Aphid infestation around the root system results inrepeated infestation of the foliage as it serves as a reservoir of aphids. In extreme cases, the apple coresare also infested, thus affecting the sale of apples. In 1962, Northern Spy was identified as a woollyapple aphid resistant rootstock and has since then formed the basis for traditional rootstock breedingprogrammes. The Er1 gene in Northern Spy confers resistance. According to one report, the naturalresistance of Northern Spy was overcome in South Africa in 1968, but this was not confirmed in anindependent study.The main objectives of this study was to firstly identify molecular markers more closely linked to thewoolly apple aphid resistance gene, Er1, than existing markers, by applying AFLP technology toselected seedlings, identified to be resistant by conventional phenotyping. If identified, these markerscan be incorporated into existing breeding programmes. Secondly, previously identified RAPD andSCAR markers were tested to determine their applicability in local populations for use in breedingprogrammes. Ultimately the segregation of the Er1 gene in South African populations can bedetermined if tightly linked markers are identified.Three families were derived from crosses of each of three resistant genotypes, namely Northern Spy,Rootstock 5 and Russian Seedling and a susceptible cultivar, Braeburn. For the three successive yearsof the study, each resistant genotype was allowed to cross-pollinate in isolation with the susceptibleparent. Two hand-pollinated families, Russian Seedling x Liberty and Russian Seedling x NorthernSpy, were also included in the study. The amplified fragment length polymorphism (AFLP) techniquewas used in an attempt to identify markers in the resistant and susceptible seedlings. No markers wereidentified using this technique. Known sequence characterised amplified regions (SCAR) and randomamplified polymorphic DNA (RAPD) markers were used due to their suitability in marker-assistedselection for woolly apple aphid resistance. Varying results were obtained with these markers and noconclusive information was acquired with regard to the segregation of the Er] gene in any of theserootstocks and crosses. This underlines the need for the development of markers that can readily beapplied in local breeding programmes. The identification and integration of such markers will greatlybenefit the local and world wide apple industries.

[发布机构] Stellenbosch University