INHERITANCE OF RESISTANCE TO LETTUCE ROOT APHID IN THE LETTUCE CULTIVARS AVONCRISP AND LAKELAND

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 m ildew resistance gene Dm6, was shown to be governed by a single domina nt gene. There were no maternal effects evident in the inheritance of this resistance. The basis of the high level of resistance which exist s in the cv. 'Lakeland' (formerly known as 'Jubilee') was also shown t o 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 o riginal cross between the parents of cv. 'Lakeland','Calmar' and 'Avon crisp' was made. Under laboratory conditions small numbers of aphids c ommence development on cv. 'Lakeland' but colonies fail to develop and under field conditions the resistance provides adequate protection ag ainst 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.