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.     

Relationships between stem canker, stolon canker, black scurf (Rhizoctonia solani) and yield of potato (Solanum tuberosum) under different agronomic conditions

Relationships between diseases caused by Rhizoctonia solani on different parts of potato plants ( Solanum tuberosum ) at different stages of crop growth were investigated under selected agronomic conditions. The effects of different densities of tuber-borne inoculum, date of planting, irrigation, size of seed tubers and their interactions on the incidence of stem and stolon canker during crop growth, the incidence and severity of black scurf and the yield of progeny tubers at harvest were quantified in a multifactorial experiment. Differences in the incidence of stem canker, stolon canker and black scurf were dominated by the effect of density of inoculum on seed tubers at planting. Highly positive correlations between the disease variables indicated a close relationship between the incidence of disease at each stage of crop growth although the degree of association between variables measured at an early growth stage and those measured at progressively later stages of crop growth weakened as the time interval increased. Total yield of progeny tubers was not affected by the density of tuber-borne inoculum although there was a shift in the size distribution, with a decrease in the yield of main-sized tubers and an increase in the yield of baker- and oversized tubers at the higher density of inoculum. Of the remaining factors, the effect of season tended to be more pronounced than any of the agronomic treatments although the use of irrigation and later dates of planting did influence the incidence of infection to a limited extent.     

Colonization of roots, stolons, tubers and stems of various potato (Solanum tuberosum) cultivars by the black-dot fungus Colletotrichum coccodes

In an attempt to better understand the importance of tuber-borne inoculum in black dot development, several potato cultivars were inoculated with various Colletotrichum coccodes isolates. Symptoms developed first on underground organs (starting 2 weeks after inoculation on roots, and later on stolons and tubers) of inoculated plants; stem infections developed only after 7–10 weeks, depending on the cultivar. Infection with C. coccodes resulted in a reduction in numbers of stolons and tubers in cv. Bintje, but not in the later maturing cv. Roseval. Significant isolate by cultivar interactions were detected from the analysis of root symptoms after inoculation of three potato cultivars (Bintje, Spunta and Desiree) with five C. coccodes isolates. Such an interaction was also detected for stolon/tuber symptoms at the latest scoring date (98 days after inoculation), but not at earlier dates (58, 70 and 84 days after inoculation). These results suggest that protocols based on root colonization might be used for investigating cultivar response to black dot and pathogenicity of C. coccodes isolates, and that some specificity exists in the reaction of potato genotypes to this pathogenic fungus.     

Studies on the interaction between the biocontrol agent,Serratia plymuthica A30, and blackleg‐causing Dickeya sp. (biovar 3) in potato (Solanum tuberosum)

Interactions between Serratia plymuthica A30 and a blackleg‐causing biovar 3 Dickeya sp. were examined. In a potato slice assay, S. plymuthica A30 inhibited tissue maceration caused by Dickeya sp. IPO2222 when co‐inoculated at a density at least 10 times greater than that of the pathogen. In glasshouse experiments, population dynamics of the antagonist and of the pathogen in planta were studied by dilution plating and confocal laser scanning microscopy (CLSM) using fluorescent protein‐tagged strains. Pathogen‐free minitubers were vacuum‐infiltrated with DsRed‐tagged Dickeya sp. IPO2222 and superficially treated during planting with a water suspension containing GFP‐tagged S. plymuthica A30. A30 reduced the blackleg incidence from 55% to 0%. Both the pathogen and the antagonist colonized the seed potato tubers internally within 1 day post‐inoculation (dpi). Between 1 and 7 dpi, the population of A30 in tubers increased from 10¹ to c. 10³ CFU g^?1 and subsequently remained stable until the end of the experiment (28 dpi). Populations of A30 in stems and roots increased from c. 10² to c. 10⁴ CFU g^?1 between 7 and 28 dpi. Dilution plating and CLSM studies showed that A30 decreased the density of Dickeya sp. populations in plants. Dilution plating combined with microscopy allowed the enumeration of strain A30 and its visualization in the vascular tissues of stem and roots and in the pith of roots, as well as its adherence to and colonization of the root surface. The implications of these finding for the use of S. plymuthica A30 as a biocontrol agent are discussed.     

The effects of topical applications of glyphosate and aminotriazole on volunteer potatoes (Solanum tuberosum)

Application of small amounts of glyphosate and aminotriazole to the top 2–3 leaves of potato stems killed those stems. Untreated stems attached to the same plant did not die, although they showed symptoms of herbicide damage. Glyphosate caused the death of the apices of the untreated stems, growth of axillary buds and sometimes aerial tuberization. Concentrations of glyphosate between 025 and 8% a.i. and of aminotriazole between 1 and 4% a.i. achieved equally good control of treated stems, although the higher concentrations worked more quickly and generally resulted in more symptoms on the untreated stems. The more stems that were treated on a particular plant, the greater the symptoms on the untreated ones. When all the stems were treated, no healthy tubers were produced; when only some were treated, both healthy and deformed tubers were found at harvest. The effects on the untreated stems are examined in relation to the translocation of glyphosate and the anatomy of the potato plant.     

Transport van X-virus in de aardappel (Solanum tuberosum L.) bij primaire infectie

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With a summary: Translocation of virus X in the potato (Solanum tuberosum L.) in primarily infected plants

     

Incidence and molecular characterization of potato leaf roll virus in seed potato production in Serbia

European Journal of Plant Pathology - The distribution and frequency of potato leaf roll virus in the four most important potato growing regions in Serbia were studied during the seven years...     

The potential for the Rapid Screening of Potato Cultivars (Solanum tuberosum) for Resistance to Powdery Scab (Spongospora subterranea) using a Laboratory Bioassay

Powdery scab of potato, once established in a field, is difficult to control because of the longevity of the resting spores (cystosori) of the causal organism, Spongospora subterranea f.sp. subterranea. Host resistance is likely to be the most efficient in a long-term control strategy for preventing build-up of field inoculum and spread of the disease. Resistance screening of potato cultivars is mostly done in laborious field trials where disease development is likely to be unpredictable. A bioassay with potato tissue cultured plantlets and cystosori as inoculum is described and was tested for its potential to screen potato cultivars at an early stage for their relative susceptibility to powdery scab by comparing the lab results with field data. With cystosori inoculum of Swiss origin, the laboratory test showed clear differences between the potato cultivars in the severity of zoosporangial root infection which correlated better with ranked tuber infection data, compared to root galling. There are apparent differences in the relative trends in susceptibility between roots and tubers of five selected cultivars when using naturally infested soil instead of prepared cystosori as inoculum in the lab bioassay. Furthermore, differences in the severity of zoosporangial root infection of two selected cultivars were found when cystosori from different countries where used as inoculum. A possible host genotype × pathogen interaction is discussed. The bioassay has the potential to screen and select for resistant material at an early breeding stage thus making field trials not unnecessary but more economical. It will allow the use of a standard set of pathogen collections and facilitate testing for inoculum virulence in infested soils.     

Seed transmission of Sweet potato leaf curl virus in sweet potato (Ipomoea batatas)

Sweet potato leaf curl virus (SPLCV) infects sweet potato and is a member of the family Geminiviridae (genus Begomovirus). SPLCV transmission occurs from plant to plant mostly via vegetative propagation as well as by the insect vector Bemisia tabaci. When sweet potato seeds were planted and cultivated in a whitefly‐free greenhouse, some sweet potato plants started to show SPLCV‐specific symptoms. SPLCV was detected by PCR from all leaves and floral tissues that showed leaf curl disease symptoms. More than 70% of the seeds harvested from SPLCV‐infected sweet potato plants tested positive for SPLCV. SPLCV was also identified from dissected endosperm and embryos. The transmission level of SPLCV from seeds to seedlings was up to 15%. Southern blot hybridization showed SPLCV‐specific single‐ and double‐stranded DNAs in seedlings germinated from SPLCV‐infected seeds. Taken altogether, the results show that SPLCV in plants of the tested sweet potato cultivars can be transmitted via seeds and SPLCV DNA can replicate in developing seedlings. This is the first seed transmission report of SPLCV in sweet potato plants and also, to the authors' knowledge, the first report of seed transmission for any geminivirus.     

Survey and molecular detection of phytoplasmas associated with potato in Romania and southern Russia

In recent years, emerging phytoplasma diseases of potato (Solanum tuberosum L.) have increasingly become important in central and eastern Europe. Accurate identification of phytoplasmas and their insect vectors is essential to developing effective management strategies for diseases caused by these plant pathogens. Potato phytoplasma diseases in Europe were for a long time diagnosed only on the basis of visual symptoms. However, this approach is not very reliable and the use of modern molecular techniques such as polymerase chain reaction (PCR) is required in order to accurately determine the etiology of these phytoplasma diseases. A survey and identification of phytoplasmas associated with potato crops in Romania and southern Russia were conducted based on modern molecular techniques. Symptomatic potato plants were collected from several fields and tested for phytoplasmas by PCR. Also, selected crops and weeds in the vicinity of these potato fields were sampled and tested for phytoplasmas. Stolbur (“Candidatus Phytoplasma solani”; 16SrXII-A) was the only phytoplasma detected in potato and adjacent crops, including tomato (Solanum lycopersicum), pepper (Capsicum annuum), eggplant (Solanum melongena), and beet (Beta vulgaris). This phytoplasma was also detected in weeds, particularly Convolvulus arvensis, Cuscuta sp., and Euphorbia falcata. Genotyping of obtained stolbur isolates on tuf genes revealed that they all had the same RFLP profile corresponding to the tuf-type ‘b’ (VK Type II). Stolbur-affected potato plants produced a large number of spongy tubers that resulted in commercially unacceptable potato chips upon processing.     

Phytotoxicity, absorption and metabolism of chlorsulfuron in monoploid callus of potato (Solanum phureia)

The mode of phytotoxic action and metabolism of chlorsulfuron was studied in non-differentiated. white monoploid potato (Solanum plureja Juz. & Buk.) callus. Dose response studies showed that the growth of callus was inhibited about 40% by 11.2 nm and 55% by 28 nM chlorsulfuron. Casein hydrolysate provided partial protection of callus against chlorsulfuron injury. Neither leucine, isoleucine. nor valine alone alleviated the growth retardation caused by the herbicide. However, the inhibition caused by the herbicide. however, the inhibition of callus growth by chlorsulfuron was reversed when the medium was supplemented with a combination of isoleucine and valine at 100 μM each. Potato callus absorbed 20 and 30% of the applied chlorsulfuron after 24 and 48 h. respectively, and less than 5% of the herbieide was metabolized by callus after 48 h of treatment. The research demonstrated the potential usefulness of monoploid callus in the investigation of phytotoxicity and mode of action of herbicides. Le mode d'action pour la phytotoxicite et le metabolisme du chlorsulfuron out ete etudies au niveau de cals monoploides indifferencies de pommes de pommes de terre (Solanum phureja Juz. & Buk) Les etudes sur l'effet does ont montre que la croissance des cals etait inhibee d'environ 40% par 11.2 nM et 55% par 28nM de chlorsulfuron Un hydrolysat de caseine protege partiellement jes cals de l'action de chlorsulfuron. Ni la leucine, Fisoleucine et la valine seules ne suffisent a annuler le retard de croissance du a Therbicide. Cependant, Finhibition de la croissance des cals par le chlorsulfuron a ete levee quand on a complemente le milieu par une association d'is-oleucine et de valine a 100&M chaque. Les cals de pomme de terre ont absorbe 20 a 30% du chlorsulfuron applique apres respectivement 24 et 48 h et moins de 5% de l'herbicide etait metabolise par les cals 48 h apres le traitement. Ces travaux demontrent Futilite potentielle des cals monoploides dans les recherches sur la phytotoxicite et le mode d'action de herbicieds. An nicht differenziertem, weissem, monoploidem Callusgewebe von Kartoffeln (Solaman phureja Juz. & Buk.) wurden die phytotoxische Wirkungsweise und der Metabolismus von Chlorsul Furon studiert. Dosis/Wirkungs-Untersuchungen zeigten. dass 11.2 und 28 Chlorsulfuron das Calluswachstum zu 40 resp. 55% hemmten. Caseinhydrolysat schutzte das gewebe teilweise gegen Chlorsulfuronschadigungen. Weder Leucin. Isolcucin oder Valin. allen eingesetzt. waren in der Lage die durch das Herbizid verursachte Wachstumshemmung zu verringern. Die Hemmung des Calluswachstums wurde jedoch aufge hoben. wenn dem Medium eine Kombination von je 100 μM von Isoleuein und Valin zugesetzt worden war. Das Callusgewebe absorbierte 20 resp. 30% des applizierten Chlorsulfuron innerhalb 24 and 48 h: weniger als 5% des herbizids war 48 h nach der Applikation metabolisiert. Die Untersuchungen zeigten die potentielle Moglich-keit monoploide Callusgewebe zur Abklarung von Phytotoxizitat und Wirkungsweise von Her-biziden einzusetzen. haploid tobacco plant to study the mode of inheritance of resistance to chlorsulfuron and metsulfuron. Scheel & Casida (1985) studied the mode of action of chlorsulfuron in soybean (Glycine max L. Amsoy 71) cell suspension caltures and obtained similar results to those reported by ray (1984) for pea seedlings. In this study we report the phytotoxicity. mode of action. and metabolism of chlorsulfuron in non-differentiated, white. monoploid potato callus.     

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.     

Characterization of a potyvirus from eggplant (Solanum melongena) as a strain of potato virus Y by N-terminal serology and sequence relationships

A potyvirus (eggplant mottle virus, EMoV) causing mosaic mottling in eggplant ( Solanum melongena ) was characterized on the basis of biological, serological and partial nucleotide sequence properties. EMoV infected Chenopodium amaranticolor and members of the Solanaceae. Polyclonal antiserum against EMoV showed antigenic relationship with henbane mosaic potyvirus (HMV) and potato Y potyvirus (PVY). Virus-specific antibodies directed to the N-terminal region of EMoV cross-reacted only with PVY. Determination and comparison of nucleotide sequence of the coat protein (CP) and the 3'-untranslated region (UTR) of EMoV with other potyviruses showed that the level of homology was highest with PVY isolates. Comparative sequence analyses of the CP amino acid and 3'-UTR sequences with distinct PVY isolates placed EMoV within the PVY^O subgroup.     

Ring rot-like symptoms in Solanum melongena caused by Erwinia chrysanthemi (potato strain) after artificial inoculation

Erwinia chrysanthemi , present in potato extracts prepared according to the EC method for detection of latent ring-rot infections, can multiply and cause ring rot-like symptoms in initial stages of disease development in the test plant Solanum melongena. Symptoms on S. melongena are described and differentiated from those caused by Clavibacter michiganensis ssp. sepedonicus.     

Giant calyx: a disease of eggplant (Solanum melongena) associated with a mycoplasma-like organism in Brazil

A disease of eggplant ( Solanum melongena ) associated with a mycoplasma-like organism (MLO) was found in the Federal District, Brazil. Symptoms were characterized by teratological changes in the flowering structure, reduction and malformation of leaves, proliferation of lateral buds, and an overall plant stunting. Evidence for the association between MLO infection and disease symptoms was obtained through graft-transmission experiments and electron microscopy. This is the first record of an eggplant disease associated with MLOs in Brazil.     

Characterization of Grapevine Algerian latent virus isolated from nipplefruit (Solanum mammosum) in Japan

Alfalfa mosaic virus (AMV), Cucumber mosaic virus (CMV), Potato virus Y (PVY), Tomato bushy stunt virus nipplefruit strain (TBSV-Nf), and an unknown spherical virus were isolated from nipplefruit (Solanum mammosum) cultivated in Chiba Prefecture, Japan. The spherical virus was identified as Grapevine Algerian latent virus nipplefruit strain (GALV-Nf) from the genus Tombusvirus, based on its physical properties, serological relationships, and analysis of genomic RNA. The genomic RNA of GALV-Nf is 4731 nucleotides long and encodes five open reading frames as well as those of other tombusviruses. Nipplefruit infected with GALV-Nf had severe stunting, leaf deformation, and clear mosaic symptoms. This is the first report of an isolation of GALV in Japan. An erratum to this article is available at .