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Seed potato crops are currently sprayed weekly with mineral oil to prevent transmission of the Potato virus Y (PVY; Potyviridae: Potyvirus), one of the most prevalent and important non-persistent viruses affecting potato production. In spite of its wide usage as inhibitor of virus transmission, the mode of action for mineral oil is poorly known. The objective of this study was to quantify the effect of dosage and time from application of mineral oil on the inhibition of PVY acquisition. The bird cherry-oat aphid, Rhopalosiphum padi (L.) (Hemiptera: Aphididae), known as vector of PVY, was used in all the experiments. The results indicated that mineral oil efficiently decreased PVY acquisition by 75 and 70% 1 day after application of 5 and 10 l ha−1, respectively. The inhibition effect decreased with time from application; mineral oil inhibits acquisition for less than 4 days at 5 l ha−1 and between 8 and 12 days at 10 l ha−1. As mineral oil was detected in the body of fewer aphids when they fed on plants 1 day after oil application, a change in the aphid probing behaviour on mineral oil-treated plants was deduced. These results support the hypothesis that mineral oil physically inhibits the binding of the virus at the tip of the stylets.

The current-season spread of Potato virus Y (PVY) was investigated in New Brunswick, Canada, in 11 potato fields planted with six different cultivars in 2009 and 2010. In all, 100 plants selected from each field were monitored for current-season PVY infections using enzyme-linked immunosorbent assay (ELISA) and real-time reverse-transcription polymerase chain reaction (RT-PCR) assay. Average PVY incidence in fields increased from 0.6% in 2009 and 2% in 2010 in the leaves to 20.3% in 2009 and 21.9% in 2010 in the tubers at the time of harvest. In individual fields, PVY incidence in tubers reached as high as 37% in 2009 and 39% in 2010 at the time of harvest. Real-time RT-PCR assay detected more samples with PVY from leaves than did ELISA. A higher number of positive samples was also detected with real-time RT-PCR from growing tubers compared with the leaves collected from the same plant at the same sampling time. PVY incidence determined from the growing tubers showed a significant positive correlation with the PVY incidence of tubers after harvest. Preharvest testing provides another option to growers to either top-kill the crop immediately to secure the seed market when the PVY incidence is low or leave the tubers to develop further for table or processing purposes when incidence of PVY is high.

Potato virus Y (PVY) is one of the most economically important viruses affecting the potato crop. Several strains of the virus, including PVYO, PVYN, recombinant isolates; PVYN:O (PVY N-Wi) and PVYNTN and several variants of PVYO have been reported from North American potato-production areas. The green peach aphid, Myzus persicae Sulzer, is a colonizer of potatoes and is considered the most important vector of PVY. The objective of this study was to measure the population growth of M. persicae on potato plants infected with different strains and genetic variants of PVY. The initial population of ten winged adults of M. persicae was allowed to develop on a potted plant for 12 days. Results clearly indicated that infections by different strains and genetic variants of PVY did not influence the population growth of M. persicae on potato plants during this period.

Potato virus Y (PVY) is one of the most economically important viruses affecting potato crops worldwide. PVY can be transmitted from potato to potato by several aphid species, most of which do not colonize the potato crop. New methods including preservation of viral RNA on stylets of aphids collected from yellow pan trap samples, polymerase chain reaction detection of PVY from the stylets of one aphid, and aphid identification using DNA barcoding were used to identify possible PVY vectors from field samples. In total, 65 aphid taxa were identified from the samples that tested positive for PVY. Among those, 45 taxa had never been evaluated for their ability to transmit PVY, and 7 were previously labeled as nonvectors. These results demonstrated that the list of PVY vectors is likely longer than previously reported and that most (if not all) species of aphids could be considered as potential vectors. This premise has important implications in the management of PVY in seed potato production.

The strain diversity and variant population of Potato virus Y (PVY) was investigated in potato lots with high PVY incidence in 2009 in New Brunswick, Canada, using reverse transcription (RT)-PCR, enzyme-linked immunosorbent assay (ELISA) and biological assays. Twenty lots with PVY infection rates >3 % were chosen following post-harvest testing for further investigation. Assays using multiplex RT-PCR revealed the existence of the common (PVYO), the recombinant N:O (PVYN:O) and the recombinant (European) potato tuber necrosis (Eu-PVYNTN) strains. PVYO was the predominant strain while PVYN:O and Eu-PVYNTN were widespread in these potato lots. PVYN:O and Eu-PVYNTN, either present alone or mixed with PVYO, were found in 19 and 13 of the 20 lots, respectively. Neither the tobacco veinal necrosis strain (PVYN) nor the non-recombinant (North American) PVYNTN was detected in the potatoes. Among the PVYO strain group, PVYO-Oz/-FL variant type was the predominant followed by the uncharacterized PVYO and the PVYO-139/-RB types. Biological assays of representative PVY positive-samples using tobacco and Yukon Gold were consistent with the findings of RT-PCR and serological assays.

Pink rot caused by Phytophthora erythroseptica is found in most major potato-growing regions of the world. The pathogen can survive for many years in soil by means of oospores which are disseminated from diseased potato tissues. The ability to detect the pathogen in soil could be a valuable management tool that enables growers to plan control strategies depending on the presence of pathogen propagules in a particular field. However, soils are one of the most challenging environmental matrices to obtain microbial DNA that will support PCR. A method was developed that combined traditional baiting technique with PCR methods to detect P. erythroseptica in infested soil samples. Hairy nightshade (Solanum sarrachoides Sendt.) and bitter nightshade (Solanum dulcamara L.) two leaf stage (TLS) seedlings and cotyledon leaves successfully baited P. erythroseptica from zoospore suspensions, artificially inoculated soils and naturally infested soils. The pathogen was detected in the bait tissue with PCR methods. PCR increased the precision of the bait test. However, time was still required for the pathogen to infect and develop on the bait tissues. Although P. erythroseptica was detected from some bait plants only after 2 days of incubation, 10 days of incubation produced consistent results across the replicates with hairy and bitter nightshade cotyledon leaves and TLS seedlings.

Pink rot of potatoes caused by Phytophthora erythroseptica is known to infect all underground potato (Solanum tuberosum) tissues such as roots, stolons, tubers and basal stems. Potato leaves and stems do not normally exhibit symptoms except when extensive infection of underground plant parts results in plant wilt, chlorosis and necrosis. This is the first study to investigate the spread of P. erythroseptica in above-ground potato tissues using both traditional isolation and PCR methods originally developed to detect the pathogen in tubers. P. erythroseptica was detected in 66% of leaf and stem tissue samples originated from artificially-inoculated and naturally-infected tubers of ‘Yukon Gold’ and ‘Shepody’ by PCR methods. However, it was only recovered in pure cultures from 38% of stem and leaf tissue samples. The pathogen was also detected in leaf and stem tissues and aerial tubers of plantlets grown in potting mixtures infested with P. erythroseptica. Pure cultures of P. erythroseptica obtained from stem and leaf tissues, together with the 95% of the detection with the real-time PCR assay and 45% with the conventional PCR assay confirmed the viability of the pathogen in above-ground potato tissues. Furthermore, the pathogen was detected in progeny tubers and stolons produced by the infected potato plants. P. erythroseptica was also detected in a few samples of debris taken from naturally senesced above-ground potato tissue after harvest.

Potato virus Y (PVY) is transmitted by aphids in a nonpersistent manner and aphid species differ in their ability to transmit PVY. During host selection, aphids will land and probe on nonhost plant species and this behavior is an important component of the epidemiology of many aphid-transmitted viruses. In this study, we hypothesized that host selection behavior varies between aphid species and the host or nonhost status of the plant and this behavior will modulate their ability to acquire PVY. Three potato colonizers, Myzus persicae (Sulzer), Macrosiphum euphorbiae (Thomas), and Aphis nasturtii (Kaltenbach) and three casual visitors to potato fields, Myzus cerasi (F.), Rhopalosiphum padi (L.), and Sitobion avenae (F.) were evaluated using two acquisition assays. In one assay, the normal host selection and feeding behavior of aphid species were eliminated using an artificial diet while the other considered the normal host selection and feeding behavior of aphid species on potato plants. PVY acquisition rates of aphid species widely differed between the two assays indicating the impact of host selection and feeding behavior on PVY acquisition. This behavior varied greatly between potato colonizers and noncolonizers. We recommend that laboratory evaluations of PVY vector efficiency consider the normal host selection and feeding behavior of aphid species on potatoes.