Aphid resistance in raspberry and feeding behaviour of Amphorophora idaei

Abstract

The raspberry aphid Amphorophora idaei is a major pest of the raspberry plant and a vector of different viruses like Raspberry leaf mottle virus (RLMV), Raspberry leaf spot virus (RLSV), Black raspberry necrosis virus (BRNV) and Rubus yellow net virus (RYNV). Aphid resistant raspberry genotypes additionally show a reduced occurrence of viruses, thus the aim of this study was to investigate whether the feeding behaviour of A. idaei differs between aphid resistant and susceptible plants. In a biotest the cultivars (cvs.)‘Titan’,‘Rumiloba’,‘Nootka’,‘Schoenemann’,‘Williamette’ and‘Autumn Bliss’ show different levels of resistance. A significantly lower population was observed after 27 d on the resistant cvs.‘Rumiloba’ and‘Autumn Bliss’ in comparison to the other cultivars tested. The number of aphids on cv.‘Nootka’ was higher than on the resistant cultivars but significantly lower than on the susceptible cvs.‘Titan’,‘Williamette’ and‘Schoenemann’. The feeding behaviour was studied over a period of 12 h on plants of the cvs.‘Rumiloba’,‘Nootka’,‘Schoenemann’ and‘Autumn Bliss’ by using the electrical penetration graph (EPG) technique. Overall between 62% and 68% aphids tested per cultivar made probes on the leaves and penetrated into the phloem. On the resistant cv.‘Rumiloba’ the aphids started to probe considerably later (49.3 min) than on the other cultivars (12.1 to 33.1 min). In contrast, the first probe on‘Rumiloba’ was shorter (2.2 min) than on the resistant cultivars (23.9 to 63.5 min). On average the aphids attained the phloem on the susceptible cv.‘Schoenemann’ considerably earlier (221.1 min) than on the resistant cultivars (349.5 to 370.4 min). On the resistant cv.‘Nootka’ significant differences were found for the duration of phloem salivation (E1-pattern, 810.9 s in comparison to 24.3 to 176.9 s), the number of phloem salivation phases (2.7 in comparison to 0.1 to 0.2) and the number of phloem contacts before the sustainable phloem feeding (> 10 min) started (1.1 in comparison to 0.1 to 0.2). No differences were found between the cultivars for the number and duration of potential drops (cell penetrations) during the pathway to the phloem, analysed during the first 2 hours of the experiments. The obtained results indicate that the probing and feeding behaviour of A. idaei, which is responsible for virus transmission, is not sufficiently different between resistant and susceptible cultivars to be the reason for virus resistance.