Did Myzus persicae (Sulzer) from potato reared on a novel host for 15 years retain its host-related properties?

Myzus persicae (Sulzer) is an important agricultural pest worldwide causing major economic losses due to its ability to transmit over 100 viruses including Potato virus Y (PVY). Myzus persicae shows considerable variation with respect to performance on its host plants. The objective of this study was to use a survival experiment, behavioural observations, including observations of probing and feeding behaviour obtained using the electrical penetration graph (EPG) technique, and a PVY acquisition experiment to determine whether or not potato was still the more suitable host for M. persicae originating on potato and reared on a novel host, table beet, for over 15 years. In a survival experiment, the pre-reproductive period was significantly longer while adult survival and whole longevity were significantly lower for M. persicae reared on beet fed beet leaves compared to M. persicae reared on potato fed potato leaves. The number of progenies produced and fecundity were both significantly reduced (90 and 85%, respectively) for M. persicae reared on beet fed beet leaves. Ethological observations and EPG assessment of M. persicae behaviour reared on beet placed on beet leaves showed significantly impaired behavioural responses compared to M. persicae reared on potato placed on potato leaves. The rate of PVY acquisition was the same for M. persicae reared on beet and on potato. These results indicate that after 15 years on table beet, M. persicae still performs better on its original host, potato, and appears to be a specialized potato-adapted genotype.

Increased sensitivity of RT-PCR for Potato virus Y detection using RNA isolated by a procedure with differential centrifugation.

The sensitivity of reverse transcription-polymerase chain reaction (RT-PCR) for virus detection is influenced by many factors such as specificity of primers and quality of templates. These factors become extremely important for successful detection when virus concentration is low. Total RNA isolated from Potato virus Y (PVY)-infected potato plants using the sodium sulfite RNA isolation method or RNeasy plant mini kit contains a high proportion of host RNA and may also contain trace amount of phenolic and polysaccharide residues, which may inhibit RT-PCR. The goal of this study was to enhance the sensitivity of PVY detection by reducing host RNA in the extract by differential centrifugation followed by extraction using an RNeasy mini kit (DCR method). One-step RT-PCR had relatively low amplification efficiency for PVY RNA when a high proportion of plant RNA was present. SYBR Green-based real time RT-PCR showed that the RNA isolated by the DCR method had a higher cycle threshold value (Ct) for the elongation factor 1-α mRNA (Ef1α) of potato than the Ct value of the RNA extracted using the RNeasy plant mini kit, indicating that the DCR method significantly reduced the proportion of potato RNA in the extract. The detectable amount of RNA extracted using the DCR method was <0.001ng when plant sap from 10 PVY-infected and PVY-free potato leaflets in a 1.5:100 fresh weight ratio was extracted, compared with 0.01 and 0.02ng of RNA using the RNeasy plant mini kit and sodium sulfite RNA isolation methods, respectively.

Effect of insecticide-treated potato plants on aphid behavior and potato virus Y acquisition.

BACKGROUND: The objective was to assess the effect of two contact insecticides, lambda-cyhalothrin and flonicamid, and three systemic insecticides, pymetrozine, dimethoate and imidacloprid, on the behavior and potato virus Y (PVY) acquisition of three aphid species, Macrosiphum euphorbiae (Thomas), Rhopalosiphum padi L. and Aphis fabae (Scopoli). RESULTS: At 1-4 days after application, contact insecticides strongly modified aphid behavior and intoxicated them. Dimethoate sprayed on potato plants did not change the behavior of the three tested aphid species, while imidacloprid slightly reduced the probing behavior of M. euphorbiae and intoxicated several R. padi. The residual effect of the insecticides (10-21 days after application) was almost non-existent. No intoxication was found, and only slight changes in the behavior of R. padi and A. fabae were observed. The acquisition of PVY by R. padi was reduced on lambda-cyhalothrin- and dimethoate-treated plants that were sprayed a few days before the test. CONCLUSION: One systemic and two contact insecticides were effective at intoxicating aphids and reducing probing behavior soon after application. Some insecticides might sporadically reduce the spread of PVY either by modifying the behavior or reducing PVY acquisition, but their action is likely limited to a short period of time after application.

Quantification of mineral oil accumulation and movement in potato plants and its significance in potato virus Y management.

BACKGROUND: Mineral oils are increasingly sprayed to manage potato virus Y (PVY). However, the mode of accumulation and movement of mineral oil in the potato plant has not been understood. This information is important for optimisation of the concentration and frequency of spraying. During the 2012 season, cvs Russet Burbank and Shepody were planted in the field and in the greenhouse, respectively, and were subjected to mineral oil treatments. The plant samples from the treatment plots were collected, and oil was extracted and quantified using gas chromatography-mass spectrometry. RESULTS: Mineral oil stayed in the vicinity of the sprayed leaves and did not move from leaflet to leaflet or from leaflet to stem, stolon, tuber or root. Following spraying, the oil content in the plant leaves diluted as time progressed. At plant maturity, leaves sampled from the greenhouse sprayed plants had about 4 times more oil content than those sampled from the field sprayed plants. Plots treated with regular spray of mineral oil showed low PVY incidences at crop harvest. CONCLUSION: The information generated in this study on the pattern of accumulation and movement of mineral oil in greenhouse- and field-grown potato plants shows that, as the oil does not move from leaflet to leaflet, frequent mineral oil sprays from crop emergence to harvest are required to prevent PVY infection in newly emerged leaflets and seasonal spread of PVY. The frequency of sprays may be kept higher from early to mid-stage, when plant growth is faster, and lower close to plant maturity.

Assessing aphids potato virus Y-transmission efficiency: A new approach.

In order to develop an alternative method to optimize the relative efficiency factor (REF) assessment, the efficiency of transmission of Potato virus Y (PVY) by seven aphid species was examined. In vitro micropropagated potato plantlets were used to experiment on phenotypically and genetically homogeneous material. Species-specific acquisition access period (AAP) on a PVY-infected plantlet was assessed for each aphid species using electrical penetration graph (EPG) technique. Aphid probing behaviour determined by EPG showed that Macrosiphum euphorbiae and Myzus persicae exhibited the shortest AAPs (15 and 11min, respectively) whereas Rhopalosiphum padi, Sitobion avenae, Brevicoryne brassicae and Acyrthosiphon pisum exhibited the longest ones (more than 30min). The transmission rate obtained for M. persicae (83.3%) was higher than the ones reported in the literature. REFs assessment showed that A. pisum and B. brassicae were poor efficient vectors while M. euphorbiae and S. avenae seemed to be efficient ones even though their respective REF were significantly lower than that of M. persicae. The species R. padi and A. fabae did not transmit PVY. The hypothesis assessed for M. euphorbiae and S. avenae and consisting in the compensation of a weak PVY-transmission efficiency by a higher number of vectors, was not supported. The use of this new method for REF evaluation and the need to consider aphid behaviour for such an assessment was discussed.

Probing behavior of apterous and alate morphs of two potato-colonizing aphids.

Secondary host plant colonization by aphids involves alate and apterous morphs to spread in the population at a large scale by flying or, at a finer one, by walking. Macrosiphum euphorbiae Thomas (Hemiptera: Aphididae) and Myzus persicae Sulzer (Hemiptera: Aphididae) are two polyphagous aphids that cause serious losses on many crops, particularly on potato, Solanum tuberosum L. (Solanales: Solanaceae). When settlement of virginoparous alate aphids occurs, apterous individuals are produced and spread within the potato field. As these two potato colonizers originate from different areas and show different body length, this study compared probing behaviors of virginoparous alate and apterous M. persicae and M. euphorbiae on one of their secondary host plants, Solanum tuberosum. Non­choice bioassays and electrical penetration graph (EPG) recordings were performed. Most M. euphorbiae of the two morphs rapidly accepted potato plants and exhibited long duration of probing, phloem sap salivation, and ingestion phases. In contrast, at the end of the experiment, most alates of M. persicae left the potato leaflet after brief gustative probes. Moreover, EPG experiments showed that the main difference between both morphs of the two species concerned the xylem ingestion parameter. Differences between species were also reported, such as an increased total duration of probing in both morphs and enhanced phloem ingestion duration in apterous M. euphorbiae. All the differences highlighted in this study are discussed according to the variations observed in aphid body size and to their historical association with Solanum species.