Particle length of various isolates of potato virus S

The normal lengths of virus particles of five isolates of potato virus S, which in previous experiments had been detected to differ extremely in translocation speed in potato plants, were found to vary only from 641 to 655 m. However, these differences are not significant and the isolates are therefore considered to have a particle length of 650 m in agreement with Brandes' recent conclusion (1967).Samenvatting Er werd vastgesteld, dat de normale lengte van de virusdeeltjes van vijf isolaten van het aardappel-S-virus, waarvan in eerder uitgevoerde proeven was aangetoond dat ze met verschillende snelheden in aardappelplanten werden getransporteerd, varieerden van 641 tot 655 m. Aangezien de verschillen in de berekende lengten onbetrouwbaar zijn moet worden geconcludeerd dat de isolaten een gelijke normale lengte bezitten. Deze kan vanwege zijn overeenstemming met de gegevens van Brandes (1967) gesteld worden op 650 m.     

Detection of potato virus Y in early-harvested potato tubers by cDNA hybridization and three modifications of ELISA1

The standard ELISA method for detection of PVY in dormant potato tubers was compared with recently developed methods: (1) a hybridization technique, using a complementary DNA-probe to PVY^N; (2) three modifications of ELISA (standard monoclonal, Flegg & Clark polyclonal or monoclonal). Sap of six Dutch cultivars secondarily infected with PVY was subjected to these methods directly after lifting and after six subsequent one-week intervals during storage at 20°C. During storage the detectability of PVY decreased, irrespective of the diagnostic method applied. However, decrease was less in susceptible than in resistant cultivars. Although the hybridization technique yielded slightly better results than the standard ELISA procedure, it was time-consuming and involved hazardous reagents. The modifications of ELISA investigated were not, in general, more sensitive than standard ELISA.     

Partial infection with potato virus YN of tubers from primarily infected potato plants

A field experiment was designed to obtain information on the extent of partial infection of Bintje potato tubers with potato virus Y^N. Data from eight fields, in which plants were artificially infected with the virus, showed that tubers with a weight lower than 30 g became infected only about half as frequently as bigger tubers; the latter were divided into three groups of 30–60 g, 60–90 g and over 90 g, but there were no significant differences in the extent of infection in these groups. In the same experiment it was found that the heel end of a tuber is less frequently infected than the rose end. This means that in testing samples of potato tubers for the presence of potato virus Y^N it is preferable to grow the rose end of the tuber.Samenvatting Een veldproef, waarbij aardappelplanten kunstmatig met aardappel-Y^N-virus werden geïnoculeerd met het doel nadere gegevens te verkrijgen omtrent de gedeeltelijke besmetting van knollen met dit virus, leverde de volgende resultaten op. Het percentage besmette knollen met een lager gewicht dan 30 g bleek ongeveer de helft te bedragen van dat van knollen in de gewichtsklassen 30–60 g, 60–90 g en de klasse zwaarder dan 90 g. Tussen de drie laatstgenoemde groepen traden geen betrouwbare verschillen in besmetting op.Verder bleek dat in alle gewichtsklassen de oogstek genomen van de top van de knol meer kans heeft met Y^N-virus besmet te geraken dan de oogstek genomen van het naveleinde van de knol. Voor de nacontrole van aardappelpoot-goed betekent dit, dat het toetsen van een oogstek van de top van een knol voor dit doel beter geschikt is dan de oogstek van het naveleinde. De knolgrootte speelt hierbij blijkbaar geen rol van betekenis, daar knollen lichter dan 30 g in het algemeen niet voor pootgoed worden gebruikt.     

Diversity of microorganisms associated with atypical superficial blemishes of potato tubers and pathogenicity assessment

Skin blemishes of potato (Solanum tuberosum L.) tubers can cause severe economical losses to production. Some blemishes are due to known pathogens and others whose causes are unknown are called atypical blemishes. The present work aims at determining the origin of superficial atypical blemishes on a set of 204 tubers coming from 12 different French regions producing potato. The diversity of fungi and Streptomyces bacteria associated with blemishes was investigated by systematic isolation followed by identification by sequencing the internal transcribed spacer of the ribosomal DNA for fungi and by sequencing the 16S ribosomal DNA for bacteria. We found a high microbial diversity represented by 349 fungal isolates belonging to at least 47 different species and 21 bacterial strains of Streptomyces sp. The most represented fungi belonged to the genera Fusarium, Rhizoctonia, Alternaria, Penicillium, and Clonostachys. The pathogenicity of representative isolates was assessed in three bioassays; two bioassays based on single inoculations in previously sterilized potting mixture, and one bioassay based on both single and double inoculations under hydroponic conditions. We fulfilled the Koch’s postulates for Rhizoctonia solani AG 3 producing sclerotia. For other fungal and bacterial strains, our results did not show any causality or relationship between a single isolate or a complex and the occurrence of the blemishes. Moreover, the observation of irregular polygonal sunken corky lesions (polygonal lesions)—the most frequent atypical blemish—on non-inoculated tubers, suggested that the atypical blemishes could as well be a reaction of the plant to stressful environmental conditions.     

Aggressive and mild Potato virus Y isolates trigger different specific responses in susceptible potato plants

Differences in the early responses of two potato cultivars, Igor and Nadine, to two isolates of Potato virus Y (PVY), the aggressive PVY^NTN and the mild PVY^N, were monitored. Microarray and quantitative real‐time PCR analyses were carried out to identify differentially expressed genes after inoculation with each virus isolate. Additionally, symptom severity and development was observed and the amount of virus isolate accumulated in systemically infected leaves was evaluated, where a significantly higher amount of PVY^NTN was detected. Microarray analysis revealed 572, 1288 and 1706 differentially expressed genes at 0·5, 12 and 48 h post‐inoculation, respectively in cv. Igor, with a similar pattern observed in cv. Nadine. Microarray and quantitative real‐time PCR results implied an earlier accumulation of sugars and lower photosynthesis in leaves inoculated with the aggressive isolate than in leaves inoculated with the mild isolate. The PVY^NTN isolate did not activate early differential expression of the Fe‐superoxide dismutase and pectin methylesterase inhibitor (PMEI) genes, indicating a delay in plant response relative to that following PVY^N inoculation. Differences in the expression of the β‐glucanase‐I gene were also observed in early plant responses to inoculation with each virus isolate.     

Molecular characterization of potato virus YN isolates by PCR-RFLP

Based on the sequence polymorphism in the 5 terminal part of the viral genome, a range of PVY^N isolates were characterized by polymerase chain reaction (PCR) followed by restriction fragment length polymorphism (RFLP). Three pairs of primers selected in the 5 non-translated and P1 protein region were tested. Two of them yielded PCR products of about 1Kb from all isolates tested. Restriction analysis of the PCR products gave two distinct electrophoretic patterns, whichever of the three enzymes was used. In this way, the 18 isolates were separated into two easily identifiable subgroups. All tuber necrosing isolates (PVY^NTN) were clustered in the same subgroup.     

Characterization of potato potyvirus Y (PVY) isolates from seed potato batches. Situation of the NTN, Wilga and Z isolates

A collection of 38 PVY isolates from seed potato batches, originating from several Western European countries, was characterized by using current biological, serological and molecular tools differentiating PVY strains and groups. The correlation between the three kinds of tests was good but not absolute. No single serological or PCR method was able to discriminate among the five isolate groups found. Twenty-nine isolates belonged to the PVY^N strain and six to the PVY^O strain. No PVY^C was found. Two other isolates reacted serologically like PVY^O, but were unable to elicit a hypersensitive response from the Ny_tbr gene and probably represent the PVY^Z group. At the molecular level, these two isolates showed a combination of both PVY^O and PVY^N and could be recombinants of these strains. Another isolate reacted serologically like PVY^O, but induced vein necrosis in tobacco, like PVY^N-Wilga. Some PVY^N isolates caused tuber ring necrosis in glasshouse conditions. These might belong to the PVY^NTN group. The PVY^NTN, PVY^N-Wilga and PVY^Z groups probably represent pathotypes within strains PVY^N and PVY^O, respectively. The present study also confirms previous reports showing a high genetic variation at the 5 end within the PVYN strain.     

Effect of foliar applications of phosphite on post-harvest potato tubers

The utilization of phosphites (Phi) could be considered as another strategy to be included in integrated disease management programmes to reduce the intensive use of fungicides and production costs. The aim of the present work was to analyze whether the beneficial effects of phosphite treatment previously observed in potato plants grown under greenhouse conditions, were reflected after harvest of field grown potatoes, both in disease protection and in yield. In addition, biochemical compounds possibly involved in induced defence responses by Phi, like phytoalexins, pathogenesis related proteins and oxidative stress enzymes were measured. Foliar applications of KPhi to field grown crops resulted in post-harvest tubers with a reduced susceptibility to Phytophthora infestans, Fusarium solani and Erwinia carotovora infections, suggesting that this compound induced a systemic defence response. An increase in phytoalexin content in P. infestans inoculated tubers obtained from Phi-treated plants suggests their participation in the defence response. Chitinase content increased 72 h after wounding or inoculation with P. infestans in tubers from KPhi-treated plants compared to wounded or infected tubers from non-treated plants. Contrary to this, the isoforms of β-1,3-glucanases analyzed did not increase in the tubers of Phi-treated plants. The increment in peroxidase and polyphenol oxidase activities indicated that these enzymes could be part of the Phi defence mechanism. No negative effects were observed in potato yield at harvest, measured as total tuber weight and dry matter, after foliar KPhi treatment. This suggests that the energetic cost involved in the defence response activation would not be detrimental to plant growth.     

Serological recognition of Streptomyces species causing scab on potato tubers

Antisera were prepared against extracts of two tyrosinase-positiveStreptomyces spp., one of which caused a “deep” and the other a “russet” scab. Tyrosinase-positiveStreptomyces isolates not reacting with either of these antisera proved to be nonpathogenic to potato tubers, with few exceptions only. Not all isolates reacting with one or both antisera, however, were pathogenic and so all the serological positive ones had to be tested for pathogenicity to potato tubers. To obtain this relative specificity the antisera had to be absorbed with an extract of a non-pathogenic tyrosinase-positive isolate.     

The movement of potato virus Y (PVY) in the vascular system of potato plants

Potato virus Y (PVY) is responsible for major viral diseases in most potato seed areas. It is transmitted by aphids in a non-persistent manner, and it is spread in potato fields by the winged aphids flying from an infected source plant to a healthy one. Six different PVY strains groups affect potato crops: PVY^C, PVY^N, PVY^O, PVY^N:O, PVY^NTN, and PVY^N-Wi. Nowadays, PVY^NTN and PVY^N-Wi are the predominant strains in Europe and the USA. After the infection of the leaf and accumulation of the virus, the virus is translocated to the progeny tubers. It is known that PVY^N is better translocated than PVY^O, but little is known about the translocation of the other PVY strains. The translocation of PVY occurs faster in young plants than in old plants; this mature plant resistance is generally explained by a restriction of the cell-to-cell movement of the virus in the leaves. The mother tuber may play an important role in explaining mature plant resistance. PVY is able to pass from one stem to the other stems of the same plant through the vascular system of the mother tuber, but it is unknown whether this vascular link between stems is permanent during the whole life of the plant. Two greenhouse trials were set up to study the spread of PVY in the vascular system of the potato plant. The PVY-susceptible cultivar Charlotte was used for both trials. It was demonstrated that all stems growing from a PVY-infected tuber will become infected sooner or later, and that PVY^N-Wi translocates more efficiently to progeny tubers than PVY^NTN. It was also demonstrated that the progressive decay of the mother tuber in the soil reduces the possibility for virus particles to infect healthy stems through the vascular system of the mother tuber. This new element contributes to a better understanding of the mechanism of mature plant resistance.     

Infectivity of metalaxyl-sensitive and -resistant isolates ofPhytophthora infestans to whole potato tubers as affected by tuber aging and storage

Potato tubers (cv. Alpha) were harvested at various time intervals after planting, or removed from storage at various times after harvest, and inoculated with different sporangial concentrations of three metalaxyl-sensitive (MS) and three metalaxyl-resistant (MR) isolates ofPhytophthora infestans. Disease parameters recorded were: (a) percentage of infected tubers; (b) percentage of blighted tuber surface area; and (c) depth of lesions. Blight was negatively correlated with tuber age both in the field and in storage. Susceptibility of tubers declined with age in the field but increased temporarily in storage.MR isolates did not differ significantly from MS isolates in percent of infected tubers but produced significantly larger and deeper lesions in tubers. Whereas inoculum concentration had a significant effect on the percent of infected tubers and of infected tuber surface area, it did not affect significantly the depth of the lesions. The results indicate that the MR isolates tested are stronger tuber blighters than the MS isolates.     

In vitro somatic growth and reproduction of phenylamide-resistant and -sensitive isolates of Phytophthora erythroseptica from infected potato tubers in Idaho

Pink rot of potato, most commonly caused by Phytophthora erythroseptica , is a major field and post-harvest problem in southern Idaho, USA, particularly since 1998 when isolates resistant to the phenylamide fungicide metalaxyl-M (mefenoxam) were detected. Isolates of P. erythroseptica were collected from infected tubers in 2001 and 2002 from six Idaho counties and tested for resistance to metalaxyl-M on amended agar. Metalaxyl-M resistant (MR) and metalaxyl-M-sensitive (MS) isolates were identified in six counties; 160 isolates were highly resistant, seven moderately resistant and 57 sensitive to metalaxyl-M with mean EC₅₀ values of 182, 23 and 0·5 mg L⁻¹ ai metalaxyl-M, respectively. Mycelial growth rates and oospore production in agar were assessed for 20 MS and 20 MR isolates at 10, 15, 20, 25 and 30°C. Growth rates of MR isolates were between 2·5 and 3·1 times greater ( P  < 0·05) than those of MS isolates at 10, 15, 20 and 25°C, and oospore production was between 6·8 and 20·5 times greater ( P  < 0·0001) for MR than for MS isolates at the same temperatures. Colony growth in V8 broth at 18°C was greater for MR than MS isolates ( P  < 0·0032). However, zoospore production at 18°C was greater for MS than for MR isolates ( P  < 0·0109), and zoospore production m m ⁻¹ of colony circumference was also greater for MS than for MR isolates, 14 191 and 9959, respectively ( P  = 0·0109). Sexual reproduction of MR isolates in nature may be greater than MS isolates, but MS isolates may be more asexually fit based on the fitness parameters studied.     

半巢式RT-Realtime PCR检测马铃薯Y病毒脉坏死株系

马铃薯Y病毒脉坏死株系(Potato virus Y,PVYn)是马铃薯中一个非常重要的病毒病害.本文根据PVYn基因组中RNA依赖的RNA聚合酶基因序列保守区域,设计合成了3条巢式PCR引物和1条TaqMAN荧光探针,建立了半巢式RT-Realtime PCR检测PVYn的新方法.该方法采用E.Z.N.ATM陕速提取植物总RNA,并有机地结合了巢式PCR和TaqMAN探针检测技术.第二步半巢式RT-Realtime PCR既是对第一步信号的进一步放大,也是对第一步PCR产物的确认,因此,检测的准确性、灵敏度比巢式PCR、Real time PCR等方法高.实验结果表明,该方法检测灵敏度可达4fg/μL植物总RNA.     

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.     

Formation of sclerotia by Rhizoctonia solani on artificial media and potato tubers

Independent of the nutrient medium and the size of Petri dish, sclerotium initials ofRhizoctonia solani AG-3 appeared after a fixed period of time. The same held for the completion of maturation of the sclerotia. Deprivation or extra supply of nutrients reduced or increased, respectively, final mass of sclerotia but did not affect the moment of initiation and of maturation. Transfer of a mycelial mat from water agar to a nutrient-rich medium caused the formation of black solid sclerotia within four days all over the mat and not only around the site of inoculation as usually occurs on rich medium. Final sclerotial mass was higher on liquid medium than on agar. The results indicate that formation of these sclerotia is not associated with cessation of linear hyphal growth or with starvation. On mature tubers, sclerotia and hyphae are spread over the whole surface. On young growing tubers sclerotia are rarely found in the immediate vicinity of lenticels. This suggests a release of inhibitory factors at these sites which diminishes during tuber maturation. Volatile exudates from underground plant parts seem to further promote the sclerotium formation. On all underground plant parts, even the roots, final sclerotial mass was higher after wounding. After haulm destruction, development of black scurf was not stimulated by a short-term trigger or by roughning of tuber surface. The observations rather suggest that the stimulation results from an increased tuber exudation of stimulatory nutrients, water and stress factors and also from a reduction of as yet unknown inhibitory factors. Results indicated that in infested soils, the estimated inoculum density at the day of haulm destruction has no predictive value for black scurf development.     

The effect of humidity on potato gangrene development in naturally contaminated tubers

During the winters of 1977/78 and 1978/79 tubers of cv. Arran Banner naturally contaminated with Phoma exigua var, foveata were kept at either high or low humidity and at 5, 10, 15 or 20 C. During the 1978/79 winter cv. Majestic tubers were stored under similar conditions at 5 and 10°C only. At monthly intervals tubers from each lot were damaged to encourage gangrene development and returned to their storage condition except the Majestic tubers which were switched from high to low humidity or vice versa and returned to the appropriate temperature. No gangrene rots developed in tubers kept at 1 5 or 20°C at either humidity. At 5 and 10°C fewer rots developed at high humidity compared with low humidity including Majestic tubers kept Initially at high humidity. Inoculum levels in soil on tubers were not markedly affected by storage conditions.