Evidence for presence of the founder Ia mtDNA haplotype of Phytophthora infestans in 19th century potato tubers from the Rothamsted archives

Late blight remained a significant disease for potato growers in Europe long after the famine of the 1840s. Of the four mitochondrial haplotypes of Phytophthora infestans, only the Ia mitochondrial DNA (mtDNA) haplotype has been identified previously in infected potato leaves from famine‐era herbarium specimens collected in England, Ireland and Europe in the 19th century. Long‐term soil fertility experiments were conducted on potato between 1876 and 1901 in Rothamsted to investigate effects of combinations of organic manures and mineral fertilizers on disease and yield. This report identifies for the first time the same Ia mtDNA haplotype of P. infestans in three diseased tubers from 1877 from the long‐term Rothamsted trials, thus providing the earliest evidence of the presence of the founder Ia mtDNA haplotype of P. infestans in potato tubers in England. Soil amendments had a significant impact on disease and yield. A real‐time PCR assay was used to detect and quantify P. infestans in tubers. The level of pathogen DNA was greatest in tubers from highest yielding plots that received combinations of inorganic nitrogenous and mineral fertilizers and least in tubers from plots with organic farmyard manures or non‐nitrogenous mineral fertilizers. The Ia mtDNA haplotype was also confirmed from diseased potato leaves during the same time period. Thus, the founder Ia mtDNA haplotype survived in potato tubers after 1846 and was present over 30 years later in the UK.     

Fusarium graminearum as a dry rot pathogen of potato in the USA: prevalence,comparison of host isolate aggressiveness and factors affecting aetiology

A 2004–2005 survey of potatoes from stores in the north‐central potato‐producing region of the USA showed that the predominant causes of dry rot were Fusarium graminearum and Fusarium sambucinum. Isolates of F. graminearum originally isolated from potato tubers with dry rot (n = 15), wheat kernels with scab (n = 15), and sugarbeet tap roots with decay (n = 5) were tested for aggressiveness to potato tubers. There were no significant differences in aggressiveness among isolates of F. graminearum, regardless of original host, as measured by their ability to cause dry rot. These findings may have implications for survival of F. graminearum inoculum since potatoes, wheat and sugarbeets are frequently used in crop rotation in the region. Fusarium graminearum required larger wounds for infection of potato tubers than F. sambucinum. Plug‐removal injury, simulating a stolon‐removal injury, resulted in equal incidence of dry rot caused by the two Fusarium species, whereas abrasion and bruising injury were sufficient for infection and dry rot development by F. sambucinum, but not F. graminearum. A change in harvest practices from vine‐killing prior to harvest to mechanical vine‐killing on the day of harvest may be a factor affecting the onset of dry rot caused by F. graminearum, since this process often causes large wounds at the stem end of the tubers when the stolon is forcibly removed.     

Performance of real‐time PCR and immunofluorescence for the detection of Clavibacter michiganensis subsp. sepedonicus and Ralstonia solanacearum in potato tubers in routine testing

This paper describes a comparison study of test methods and supports the use of real‐time polymerase chain reaction (PCR) for the detection of Clavibacter michiganensis subsp. sepedonicus and Ralstonia solanacearum in potato tubers in routine testing. These 2 bacteria are quarantine organisms under European Union (EU) regulatory control and testing for (latent) infections of these bacteria in seed potatoes is mandatory. Real‐time PCR tests were performed on 276 routine potato tuber samples, including samples infected with either C. michiganensis subsp. sepedonicus or R. solanacearum, and the performance of these real‐time PCR tests was compared with that of immunofluorescence (IF). Real‐time PCR tests, using different primer sets and extraction and PCR protocols, proved to be sensitive and specific for the detection of C. michiganensis subsp. sepedonicus and R. solanacearum in potato tubers in routine testing, and performed at least as well as IF. Real‐time PCR is a good addition to the detection protocols as laid down in EU regulations (EU Council Directives 2006/56/EC and 2006/63/EC).     

New Zealand perspective on ISO 17025 accreditation of a plant diagnostic laboratory1

Four plant diagnostic laboratories in New Zealand have obtained ISO 17025 accreditation since 2001: Linnaeus Laboratory; PestLab, AsureQuality Ltd; Horticulture and Food Research Institute of New Zealand Ltd; and the Ministry of Agriculture and Forestry's (MAF) Plant Health and Environment Laboratory (PHEL). The challenge of pursuing ISO 17025 accreditation for PHEL emerged in late 2003 when a review of a MAF diagnostic standard made ISO 17025 accreditation a mandatory requirement for approval. The accreditation project took three years from initiation to accreditation in 2007. The scope of PHEL's accreditation covers tests (e.g. PCR, RT‐PCR, or ELISA) for the Carlavirus group, High plains virus, Iris yellow spot virus, Pepino mosaic virus, Plum pox virus, Raspberry ringspot virus, phytoplasmas, Potato spindle tuber viroid, and Xylella fastidiosa and morphological identifications of fungi and invertebrates. This article provides a brief overview of ISO 17025 accreditation of plant diagnostic laboratories in New Zealand, describes PHEL's scope of accreditation, and discusses some of the issues and challenges PHEL faced during the process of attaining accreditation and still faces post‐accreditation.     

The importance of the infected seed tuber and soil inoculum in transmitting Potato mop‐top virus to potato plants

Potato mop‐top virus (PMTV), the cause of spraing in potato tubers, is transmitted by Spongospora subterranea, the cause of powdery scab, and by planting infected seed tubers. This study was undertaken to determine the relative importance of these sources of infection in seed potato production in Scotland. The transmission of PMTV from tested seed tubers to daughter plants was examined over 2 years and six cultivars. The development of foliar symptoms varied with year and cultivar. Infection of daughter tubers derived from PMTV‐infected seed tubers was more prevalent on plants affected by foliar symptoms than those without symptoms. The rate of transmission of PMTV from infected seed tubers to daughter tubers ranged from 18 to 54%. Transmission was affected by cultivar and by origin of seed tubers used for a cultivar, but not by a cultivar's sensitivity to PMTV infection. The incidence of PMTV in daughter tubers of cv. Cara grown from seed potatoes from one source (common origin) by more than 25 seed producers was examined over two successive generations. The incidence of PMTV in daughter tubers was not correlated with that in the seed tubers but appeared to be strongly associated with soil inoculum. The incidence of PMTV was correlated with powdery scab in those crops in which both were present. There was some evidence from soil tests conducted in 2006 using a tomato bait plant and real‐time RT‐PCR that planting PMTV‐infected seed potatoes could increase the risk of introducing the virus into land not infested by PMTV.     

The MeloTuber Test: a real‐time TaqMan® PCR‐based assay to detect the root‐knot nematodes Meloidogyne chitwoodi and M. fallax directly in potato tubers

Potato is one of the many important hosts for the root‐knot nematodes Meloidogyne chitwoodi and M. fallax that can infest roots as well as tubers. In the latter they may cause surface galls and necrotic spots below the skin. In the EU these pathogens are categorized as quarantine organisms and are therefore regulated. Phytosanitary measures (PMs) are implemented and one aspect involves diagnostic procedures to detect these pathogens. To date, visual screening of external and internal symptoms is combined with the specific identification of these pests, either through microscopy, biochemical or molecular tests. A disadvantage of all these tests is the requirement of the prior extraction of nematodes from the tubers, which is not suitable for high‐throughput screening. This paper describes the MeloTuber Test developed to simultaneously detect M. chitwoodi and M. fallax by triplex real‐time TaqMan^® PCR directly in secondary potato tuber peelings. DNA extraction is carried out in a 96‐well plate of pooled secondary peelings from one hundred tubers. The analytical sensitivity is such that a single female can be readily detected in such a sample size. The validation data, described here, prove the suitability of this molecular test for the detection of M. chitwoodi and M. fallax in large scale screening tests.     

Necrotic diseases caused by viruses in Swedish potato tubers

Potato tuber necrosis in the form of spraing symptoms is caused by infection with Potato mop‐top virus (PMTV) or Tobacco rattle virus (TRV); spraing has become more important in the Swedish potato crop production. In this study, the presence in Sweden of three potato‐infecting viruses associated with necrotic symptoms in tubers was demonstrated: PMTV, TRV and Tobacco necrosis virus (TNV). This study shows that both PMTV and TRV are frequent in Swedish potato fields. PMTV was found in all Swedish counties, except the two most northern ones. TRV was present at several locations in southern and up to the central parts of Sweden. Both viruses were found further north than observed in earlier surveys. PMTV and TRV were analysed in tubers with spraing symptoms and it was not possible to decide visually if the symptoms were caused by either PMTV or TRV. Furthermore, a high occurrence of symptomless tuber infections was observed for several potato cultivars. A unique observation from this study was a mixed infection of both PMTV and TRV in tubers of cv. Berber, where no visual differences on symptom development were detectable for these tubers compared to single infections. During the survey, tubers of cv. Melody were found to display necrotic symptoms in the skin that are characteristic for the ABC disease. This suggested infection by TNV, which also could be confirmed.     

Direct tuber testing for Potato Y potyvirus by real‐time RT‐PCR and ELISA: reliable options for post‐harvest testing?*

The method currently used for testing potato tubers for viruses following harvest involves a growing‐on test. This takes up to 6 weeks to complete, and there is therefore a demand for more rapid test results. The sensitivity and reliability of direct tuber testing by DAS‐ELISA and real‐time RT‐PCR (TaqMan) were compared with the growing‐on test. In addition, the reliability of all three methods for the detection of Potato Y potyvirus (PVY) in tubers was compared over post‐harvest intervals of 6, 10, 14 and 18 weeks. The test material came from plots of tubers (cv. ‘Maris Piper’) containing a primary infection of strains PVY^N and PVY^O, following aphid transmission from marked infector plants grown during the 2003 season. Sample material was homogenized and divided, to provide comparative test material for detection of PVY by ELISA and real‐time RT‐PCR. Tuber eye‐plugs were then taken and subjected to the growing‐on test. The remainder of the tuber was also grown on and tested, to ensure infection was not missed as a consequence of an uneven distribution of virus throughout the tuber material. The results obtained using the two methods for direct testing of the tubers, and those results obtained from the traditional growing‐on test, are compared. The advantages and disadvantages of each method are discussed.     

Computer aids for plant protection in Latvia*

The main agricultural crops where decision support systems (DSS) can be used via the Internet in Latvia are winter and spring cereals and potato. Two PC‐based models, forming part of a Danish DSS, were tested under the agroecological conditions of Latvia in 1999/2002: PC‐Plant Protection to control diseases in cereals and several modifications of the NegFry model for prediction of potato late blight. The results of 4 years of trials suggest that models that satisfy the needs of one pest may not fit another. The main reasons for failure to adapt PC models are differences in cultivar susceptibility, differences in pathogenicity, simultaneous action of other organisms and spatial placement of crops (forests, rivers and fallow land). For example, it is well known that, with the recent global migration of more aggressive strains and populations of Phytophthora infestans, late blight epidemics have become less predictable and, at the same time, less controllable in potato‐growing areas. For cereals, there is a different spectrum of prevailing pathogens, causing different levels of damage, requiring incorporation into models of thresholds corresponding to local conditions. Data from weekly monitoring of local fields, warnings about the local situation and meteorological information via the Internet are the most important computer‐aided elements for experts in plant protection.     

The yam nematode (Scutellonema bradys), a potential threat to potato (Solanum tuberosum) production in West Africa

Potato (Solanum tuberosum) production in Africa is rapidly expanding and becoming increasingly important. As its geographical production range broadens, so does its potential to host new pests and diseases. Following the discovery that potato can be affected by Scutellonema bradys, further studies were undertaken to assess its potential pathogenicity on potato under screenhouse and field conditions, and on marketed tubers. Potato plants inoculated with S. bradys produced tubers with substantial cracking and evident tuber rot, compared with tubers from uninoculated plants. Symptoms of nematode infection on tubers included a scaly appearance, surface cracking as well as deeper tissue cracks, distortions, and darkened surface patches. In most cases these patches were related to sub‐surface rot. Nematodes were recovered from the soil, roots and tubers of inoculated plants. Eight weeks after inoculation, the reproduction factor of the nematode was greatest (2·0) at the lowest inoculation rate assessed (1000 nematodes per 2·5‐L pot) and least (0·4) at the highest inoculation rate (5000 nematodes per pot). In the screenhouse, potato tuber weights were low and mostly unaffected by nematode inoculation rate, except at 5000 nematodes per pot. In the field, non‐inoculated plants yielded over nine times more tubers than plants inoculated with 2000 S. bradys. Low densities of S. bradys were also recovered from 10 of 15 (67%) samples collected from market stalls, indicating field infection. This study confirms that potato can host and be damaged by S. bradys, raising its prospect as a likely significant biotic constraint to the crop.     

Investigations on potato mop-top furovirus in Sweden1

Potato mop-top furovirus (PMTV) was isolated for the first time in Sweden in 1985. During 1986 and 1987, soil samples from potato fields, mainly in the south-west of Sweden, were tested for PMTV. The virus was detected in 49 out of 305 samples tested. PMTV was also found to be present in soil collected from potato riddles during potato grading in early spring. The soil samples were tested by using Nicotiana clevelandii and N. debneyi as bait plants in a glasshouse. Seven potato cultivars were grown in a PMTV-infested field. PMTV symptoms in the tubers, i.e. external and/or internal brown rings and arcs (spraing), were observed in cvs Evergood, Provita, Saturna and Ukama but not in cvs Bellona, Bintje or King Edward. Very few, or no, PMTV symptoms were found in tubers of susceptible cultivars when examined 2-3 weeks after lifting. In later examinations spraing appeared and increased. The increase was greater in tubers stored at 9°C than in those at 4°C, and in cut than in uncut tubers.     

Detection of the root lesion nematode Pratylenchus penetrans in potato tubers

The root lesion nematode Pratylenchus penetrans parasitizes a wide range of economically important crops, including potato (Solanum tuberosum). Damage by P. penetrans impacts not only the potato yield but can also reduce the tuber quality. Detailed information on tuber infection by P. penetrans is scarce for most cultivars and molecular detection of nematodes from infected tubers is needed. The objective of this study was to assess tuber symptomatology due to P. penetrans infection in 10 potato cultivars and to provide an accurate molecular methodology for nematode detection using tuber peels. Sprouts of certified potato seed from cultivars Agata, Agria, Camel, Désirée, Dirosso, Kennebec, Laura, Picasso, Royata, and Stemster were planted in 2 L pots, and soil was inoculated with 4 P. penetrans/g of soil. Sixty days after inoculation, tubers were harvested, inspected for lesions, and the number of nematodes/g of potato peel assessed. Observations of tubers with symptoms showed the presence of P. penetrans in superficial layers of peels around the lenticels and injured necrotic tissue. Different nematode stages were detected in tubers of all inoculated cultivars, varying from 4 to 46 nematodes/g of potato peel. Species-specific primers showed suitable sensitivity and reproducibility for the detection of P. penetrans in tuber potato peel samples. The molecular detection of P. penetrans directly from tuber peels can facilitate routine nematode inspections of potato seed tubers or cull potatoes for nematode detection, and prevent further dissemination of this species.     

Epitrix similaris and Epitrix cucumeris in Portugal: damage patterns in potato and suitability of potential host plants for reproduction

The potato flea beetle species Epitrix similaris and Epitrix cucumeris were identified in mainland Portugal in 2009. This was the first finding of the species E. similaris in the EPPO region, and the first report of the species E. cucumeris, established in the Atlantic Islands of Azores (Portugal) for three decades, in the mainland EPPO zone. Preliminary information on the damage patterns caused by E. similaris and E. cucumeris on potato and their host plant preferences is provided. Leaf feeding by the adults causes the characteristic shot‐hole pattern common to flea beetles. The larvae of both species develop on the root system and cause damage to the tubers. In field experiments, tuber damage by E. similaris presented three patterns: superficial tracks (serpentines), black splinters, and shallow holes. In the laboratory E. cucumeris was observed to be able to feed on very small immature tubers, causing serpentines and holes as well. However, in some cases it developed exclusively on roots. The adults of both Epitrix species hardly fed and reproduced on sweet pepper plants but fed and reproduced on the remaining five solanaceous plants tested (aubergine, Datura stramonium, tomato, potato and Solanum nigrum). E. similaris produced a much higher number of progeny on potato and on S. nigrum than on the other host plants. E. cucumeris produced more offspring on S. nigrum than on the other host‐plants.     

Identification ofTomato Mottle Taino Begomovirus strains in Cuban potato fields

The presence of a begomovirus in potato plants with yellow mottle symptoms was determined for the first time in Cuba. The incidence of typical begomovirus-like symptoms in potato plants in some regions of Havana province (Güira de Melena, San José de las Lajas, Güines and Boyeros) during the growing seasons from 1992 to 1998 was in general low. However, in some cultivars belonging to the National Program for Potato Genetic Improvement, the incidence reached 100%. Yield losses, determined in 1992 and 1994, ranged as high as 19% to 56.33% depending on the cultivar. Characterization of the causal agent was done by light microscopy, host range (graft and mechanical transmission), DNA hybridizations, polymerase chain reaction, and restriction fragment length polymorphism analysis. Nucleotide sequence of the amplified fragments revealed the presence ofTomato mottle Taino virus. The virus was transmittedvia tubers and has been detected in mixed infections withPotato virus X and withPotato leaf roll virus. http://www.phytoparasitica.org posting Oct. 20, 2003. The first two authors contributed equally to this work.     

Development time and fecundity of the white peach scale,Pseudaulacaspis pentagona, in Turkey

The white peach scale (WPS),Pseudaulacaspis pentagona (Targioni-Tozzetti) (Homoptera: Diaspididae), is a worldwide polyphagous scale insect. It is widely distributed in Turkey, where it is the main pest of peach trees. The development and fecundity ofP. pentagona were examined at different temperatures and on different hosts in the laboratory; from these data, life tables were constructed and intrinsic rates of increase were calculated. The longevity of WPS decreased with a rise in temperature. At 25°C the largest number of crawlers (76.1 crawlers/female) was observed. The development time of WPS was generally longer on peach than on squash or potato; fecundity was higher on potato than on the other hosts, potato tubers and peach trees.     

Direct infection of potato tubers by the root parasite Orobanche aegyptiaca

Parasitic plants of the Orobanchaceae are known as obligate root parasites that develop haustoria that connect to roots of various host plants. This article describes, for the first time, a case where the root parasite successfully connected to potato tubers, i.e. to the swollen portion of an underground stem rather than to a root. The rhizosphere of Orobanche aegyptiaca and of its host Solanum tuberosum (potato) was carefully examined. In anatomical studies, the adventitious roots were directly connected to potato tubers. Numerous secondary haustoria, which developed along the adventitious roots in close vicinity to the potato tuber, penetrated the tuber epidermis and the perimedullary tuber parenchyma and developed xylem strands that are presumably connected to the minor xylem strands within the tuber cortex. These findings indicate that parasites of the Orobanchaceae that normally attack host roots may also parasitise underground stem tubers.     

Factors affecting the development and control of black dot on potato tubers

Field trials were carried out over a 4 year period (2004–2007) to determine the effect of agronomic factors, specifically cultivar resistance, irrigation, crop duration and chemical control (in‐furrow application of azoxystrobin), on black dot development on potato tubers grown in fields where soilborne inoculum of Colletotrichum coccodes was present. In 2004, 2005 and 2006, two field trials were performed each year and in 2007, 19 mini‐field trials were carried out across Scotland and England. Cultivar resistance was clearly demonstrated to be an effective method of reducing black dot disease severity on tubers (described here as the percentage of unmarketable tubers, i.e. those with symptoms covering a surface area of >10%). In the four field trials carried out in 2004 and 2005, in irrigated and fungicide‐untreated plots, 43·8% of tubers of cv. Maris Piper were unmarketable, compared with 17·0% of tubers of cv. Sante. Assessments of disease development on underground plant parts (stems, stolons and roots) revealed that cultivar resistance acted only at the tuber level, as disease symptoms on other parts were often high irrespective of published disease resistance ratings. Irrigation increased the severity of disease on tubers in two trials (England 2004 and 2006), but its effect was less significant when rainfall was high. Delaying harvest by 2 weeks increased disease severity in all six trials, whilst application of azoxystrobin consistently reduced black dot severity. There were significant interactions between factors. The results clearly show how black dot disease severity can be reduced through an integrated approach to disease management.     

Anoplophora species in Europe: infestations and management processes1

By the end of summer 2005, four sites of infestation by Anoplophora glabripennis (Coleoptera, Cerambycidae) had been detected in three European countries: Austria in 2001, at Braunau am Inn; France in 2003, at Gien, and in 2004, at Sainte‐Anne‐sur‐Brivet; and Germany in 2004, at Neukirchen am Inn. Two sites of infestation by Anoplophora chinensis have been detected in two European countries: Italy in 2000, at Parabiago, and France in 2003, at Soyons. The history of the A. glabripennis and A. chinensis discoveries is presented, as well as the respective management responses (monitoring and destruction of the infested trees). By the end of summer 2005, the eradication was not yet fully achieved in any of the four A. glabripennis‐infested sites. In contrast, no new A. chinensis‐infested trees had been found at Soyons, France, since 2003. At Parabiago, Italy, monitoring is taking place: the A. chinensis infestation affects 16 municipalities over more than 60 km². By summer 2005, destruction on a large scale of the infested trees had not yet taken place, but tree‐cutting of more than 1000 trees had been planned for winter 2005‐06. Given the current substantial extent of the A. chinensis infestation near Milan, and the density of the established A. chinensis populations, there is a high probability that the status of the pest in Italy will soon be raised from ‘introduced’ to ‘invasive’.