The inheritance of resistance in two lettuce cultivars to lettuce root aphid, Pemphigus bursarius, was studied in a series of laboratory and field experiments at Wellesbourne between 1989 and 1992. A source of total resistance in the cv. 'Avoncrisp' which is linked to the downy mildew resistance gene Dm6, was shown to be governed by a single dominant gene. There were no maternal effects evident in the inheritance of this resistance. The basis of the high level of resistance which exists in the cv. 'Lakeland' (formerly known as 'Jubilee') was also shown to be controlled by the same dominant gene. The linkage between Dm6 and root aphid resistance was broken in 'Lakeland' as this cultivar does not possess the Dm6 gene. The linkage was presumably broken when the original cross between the parents of cv. 'Lakeland', 'Calmar' and 'Avoncrisp' was made. Under laboratory conditions small numbers of aphids commence development on cv. 'Lakeland' but colonies fail to develop and under field conditions the resistance provides adequate protection against the pest. The resistance in both 'Avoncrisp' and 'Lakeland' was effective against a population of lettuce root aphid collected from an endive crop in southern France as well as being effective against the Wellesbourne population of this aphid. Crute I R, Dunn J A. 1980. An association between resistance to root aphid (Pemphigus bursarius L.) and downy mildew (Bremia lactucae Regel) in lettuce. Euphytica 29:483-488. Dunn J A. 1968. Resistance of lettuce to attack by lettuce root aphids. Varietal resistance. Report of the National Vegetable Research Station for 1967, pp. 73-74. Dunn J A. 1974a. Study on inheritance of resistance to root aphid, Pemphigus bursarius, in lettuce. Annals of Applied Biology 76:9-18. Dunn J A. 1974b. The influence of host plant on the production of sexuparae in the aphid Pemphigus bursarius. Entomologia experimentalis et applicata 17:445447.
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