Abstract
Aphid saliva can suppress the blocking of sieve elements, a reaction that plants employ to inhibit aphid feeding, but aphid saliva can also elicit plant defence responses. Such plant responses might affect interactions between different aphid species and intraspecifically, e.g. among different biotypes. The objectives of our study were to investigate if feeding behaviour and performance of two biotypes of the lettuce aphid Nasonovia ribisnigri are affected by (1) feeding by the other biotype and (2) feeding by the green peach aphid Myzus persicae or the potato aphid Macrosiphum euphorbiae. Additionally the effect of feeding in a group was studied. All experiments were performed on both a resistant and an isogenic susceptible lettuce cultivar. Feeding or probing by conspecific or heterospecific aphids had different effects on Nasonovia ribisnigri biotypes. Aphids were only slightly affected by feeding or probing of the same biotype on both susceptible and resistant lettuce. N. ribisnigri virulent biotype Nr:1 suppressed the resistance against Nr:0 in the resistant cultivar. In contrast, defence was induced by Nr:1 against Nr:0 in susceptible lettuce. Co-infestation by M. euphorbiae and M. persicae had minor effects on Nr:0. Defence against Nr:1 was induced on both susceptible lettuce and resistant lettuce by Nr:0 and M. euphorbiae. Additionally, M. persicae induced defence in resistant lettuce against Nr:1. Effectors in the saliva of Nr:1 aphids are likely responsible for the defence suppression in lettuce. Identification of these effectors could lead to a better understanding of the mechanism of virulence in N. ribisnigri.
Highlights
Nasonovia ribisnigri (Mosely), the black currant-lettuce aphid, is an important pest of lettuce, causing significant economic losses in the lettuce industry (McCreight 2008)
To study the effect of feeding in a group, we investigated the effect of feeding by the same biotype on Nr:0 and Nr:1 aphids on the two lettuce cultivars
Nr:1 aphids in a group on Terlana displayed a higher number of probes (P = 0.001) compared to single aphids on Terlana (Table 2; Fig. 1d)
Summary
Nasonovia ribisnigri (Mosely), the black currant-lettuce aphid, is an important pest of lettuce, causing significant economic losses in the lettuce industry (McCreight 2008). Control of this aphid was based on host plant resistance conferred by the Nr-gene, originating from Lactuca virosa L. (a distant wild relative of cultivated lettuce), which provided near-complete resistance against this aphid (Reinink and Dieleman 1989) This resistance, is no longer effective, because virulent populations of N. ribisnigri, designated as biotype Nr:, have been reported infesting resistant lettuce since 2007 (Thabuis et al 2011). It is hypothesised that the ability of virulent aphid biotypes to overcome R-gene-based resistance could be attributed to the loss or modification of avirulence gene products, thereby suppressing plant defences and/or evading recognition by the plant (Hogenhout and Bos 2011; Parker and Gilbert 2004)
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