Induced senescence promotes the feeding activities and nymph development of Myzus persicae (Hemiptera: Aphididae) on potato plants.

The effect of dark-induced senescence on Solanum tuberosum L. (Solanales: Solanaceae) plants was assessed on the feeding behavior and performance of the green peach aphid, Myzus persicae Sulzer (Hemiptera: Aphididae). Senescence was induced by covering the basal part of the plant with a black cloth for 5 d, avoiding the light passage, but keeping the apical buds uncovered. The basal part of control plants was covered with a white nonwoven cloth. The degree of senescence was determined by measuring the chlorophyll content of the covered leaves. The performance and feeding behavior of M. persicae were studied on the uncovered nonsenescent apical leaves. The aphid's performance was evaluated by measuring nymphal mortality and prereproductive time. Aphid feeding behavior was monitored by the electrical penetration graph technique. In plants with dark-induced senescence, the aphids showed a reduction in their prereproductive time. Aphids also spent more time ingesting sap from the phloem than in control plants and performed more test probes after the first sustained ingestion of phloem sap. These data suggest that M. persicae's phloem activities and nymph development benefit from the nutritional enrichment of phloem sap, derived from dark-induced senescence on potato plants. The induced senescence improved plant acceptance by M. persicae through an increase in sap ingestion that likely resulted in a reduction in developmental time.

Response of Solanum tuberosum to Myzus persicae infestation at different stages of foliage maturity.

Young leaves of the potato Solanum tuberosum L. cultivar Kardal contain resistance factors to the green peach aphid Myzus persicae (Sulzer) (Hemiptera: Aphididae) and normal probing behavior is impeded. However, M. persicae can survive and reproduce on mature and senescent leaves of the cv. Kardal plant without problems. We compared the settling of M. persicae on young and old leaves and analyzed the impact of aphids settling on the plant in terms of gene expression. Settling, as measured by aphid numbers staying on young or old leaves, showed that after 21 h significantly fewer aphids were found on the young leaves. At earlier time points there were no difference between young and old leaves, suggesting that the young leaf resistance factors are not located at the surface level but deeper in the tissue. Gene expression was measured in plants at 96 h postinfestation, which is at a late stage in the interaction and in compatible interactions this is long enough for host plant acceptance to occur. In old leaves of cv. Kardal (compatible interaction), M. persicae infestation elicited a higher number of differentially regulated genes than in young leaves. The plant response to aphid infestation included a larger number of genes induced than repressed, and the proportion of induced versus repressed genes was larger in young than in old leaves. Several genes changing expression seem to be involved in changing the metabolic state of the leaf from source to sink.

Comparative analysis of Solanum stoloniferum responses to probing by the green peach aphid Myzus persicae and the potato aphid Macrosiphum euphorbiae.

Plants protect themselves against aphid attacks by species-specific defense mechanisms. Previously, we have shown that Solanum stoloniferum Schlechtd has resistance factors to Myzus persicae Sulzer (Homoptera: Aphididae) at the epidermal/mesophyll level that are not effective against Macrosiphum euphorbiae Thomas (Homoptera: Aphididae). Here, we compare the nymphal mortality, the pre-reproductive development time, and the probing behavior of M. persicae and M. euphorbiae on S. stoloniferum and Solanum tuberosum L. Furthermore, we analyze the changes in gene expression in S. stoloniferum 96 hours post infestation by either aphid species. Although the M. euphorbiae probing behavior shows that aphids encounter more probing constrains on phloem activities-longer probing and salivation time- on S. stoloniferum than on S. tuberosum, the aphids succeeded in reaching a sustained ingestion of phloem sap on both plants. Probing by M. persicae on S. stoloniferum plants resulted in limited feeding only. Survival of M. euphorbiae and M. persicae was affected on young leaves, but not on senescent leaves of S. stoloniferum. Infestation by M. euphorbiae changed the expression of more genes than M. persicae did. At the systemic level both aphids elicited a weak response. Infestation of S. stoloniferum plants with a large number of M. persicae induced morphological changes in the leaves, leading to the development of pustules that were caused by disrupted vascular parenchyma and surrounding tissue. In contrast, an infestation by M. euphorbiae had no morphological effects. Both plant species can be regarded as good host for M. euphorbiae, whereas only S. tuberosum is a good host for M. persicae and S. stoloniferum is not. Infestation of S. stoloniferum by M. persicae or M. euphorbiae changed the expression of a set of plant genes specific for each of the aphids as well as a set of common genes.