Plant-mediated interactions between the potato cyst nematode, Globodera pallida and the peach potato aphid, Myzus persicae

This study elucidated the relationship between the potato cyst nematode, Globodera pallida and the peach-potato aphid, Myzus persicae, two pests that can infect the potato plant and often so simultaneously. The biological, biochemical and molecular responses of potato plants suffering nematode and aphid stress were characterised both singly and in combination. It was established that the reproductive success of aphids was significantly greater on potato plants pre-infected with nematodes compared to non-infected control plants. Endogenous levels of salicylic acid (SA) increased systemically in the leaves of potato plants following nematode and aphid infection singly with a corresponding increase in expression of the SA-mediated marker gene PR-5. Measurements of endogenous levels of jasmonic acid (JA) as well as the expression of JA-mediated defence genes increased in plants infected with aphids but were suppressed when plants were co-infected with both nematodes and aphids. This suppression of JA in co-infected plants shows a different and unique response to that found when the plant was infected with either pest in isolation. These results may indicate antagonistic crosstalk between molecular pathways in the plant following infection of the plant with G. pallida and M. persicae. M. persicae had a negative amensalism effect on G. pallida below-ground whereby pre-infestation of potato plants with M. persicae stimulated a significantly lower cumulative hatch of second-stage juveniles (J2s) when cysts of G. pallida were incubated in root diffusates from aphid-infested plants. A dose-dependent response was responsible for this with the presence of 50 aphids on the foliar parts of the plant causing a significant reduction in the emergence of J2s from cysts. Sequence of arrival experiments showed that pre-infestation of M. persicae significantly reduced the infection rate of G. pallida. This work comprises the first study into dual nematode and aphid attack in the potato crop and the study highlights how multiple stresses elicit a unique molecular response to attack compared to singly stressed plants.