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was confirmed by RT-PCR as well as by sequencing the virus genomes. It is the first time that WSSMV and furoviruses are reported on wheat in Belgium. These mosaics might represent a new threat for cereal growers in this country, but their actual impact on yield and the resistance potential of cultivars currently grown in Belgium have first to be assessed. This could also represent a new challenge for Belgian cereal breeders.

This work is performed in the frame of a research project funded by the Ministry of the Walloon Region.

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REACTION OF PLANTS OF PLUM CV. JOJO ON INFECTION WITH THREE DIFFERENT STRAINS OF PLUM POX VIRUS.

Polák J., Pívalová J., Svoboda J.

Research Institute of Crop Production, Division of Plant Medicine, Drnovská 507, 161 06 Prague 6, Czech Republic e-mail:polak@vurv.cz

Trees of plum Prunus domestica L., cv. Jojo declared as absolutely resistant or hypersensitive to PPV were inoculated by budding with three different strains of PPV. For inoculation PPV-M, PPV-D, and PPV-recombinant (PPV-M x PPV-D) were used, isolated from plum in the Czech Republic. Results of two years evaluation of inoculated plum trees are presented. Different responses of plum trees cv. Jojo to the inoculation with three PPV strains was proved. Strong hypersensitive reactions appeared in the next year after inoculation with PPV-M and PPV-recombinant strains. Not all inoculated trees died. PPV must be present in the tissue of plants cv. Jojo because the virus was transferred via cv. Jojo to the rootstock St. Julien. Plants of rootstock became systemic infected with PPV-M and PPV-recombinant strains, showing severe PPV symptoms. The presence of PPV was proved by ELISA in leaves of rootstock St. Julien, but not in leaves of cv. Jojo. Partial hypersensitive reaction of plants cv. Jojo appeared after inoculation with PPV-D strain. Recovering of plants cv. Jojo from PPV-D infection was observed after partial dying of shoots.

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Characterization of plant pathogenic bacteria associated with premature dying of apricot trees in the Czech Republic

Krejzar V., Jeřábková J., Kůdela V.,

Research Institute of Crop Production, 161 06 Prague-Ruzyně, Czech Republic, e-mail: krejzar@vurv.cz

Sixty two isolates of fluorescent pseudomonads were isolated from infected apricot trees on tree localities in south Moravia. Of the 54 fluorescent pseudomonads isolated, 94% were identified as Pseudomonas syringae pv. syringae van Hall (Pss) and 6% as Pseudomonas fluorescens (Trevisan) Migula 1895 (Pf). None of fluorescent isolates belonged to Pseudomonas syringae pv. morsprunorum (Wormald 1893) Young, Dye & Wikie 1978 (Pmp). Of the 25 isolates that expressed ice nucleation activity, 88% ranged to Pss and 12% to Pf. In pathogenicity test on immature cherry fruits, all Pss isolates were pathogenic and all Pf isolates were non-pathogenic. Pss isolates showed slight differences in biochemical characteristics (e.g. in utilisation of L-histidine, psicose and D,L-carnitine and in gelatine liquefaction) as well as in pathogenicity (according to size of necrosis in immature sweet cherry tees) and ice nucleation activities. Some Pss isolates nucleated ice at temperature as warm as -1°C, another isolates nucleated at temperature near to -5°C.

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Possibility to detect non-fluid strains of Clavibacter michiganensis pv. sepedonicus in potato tuber macerate

Jeřábková R., Krejzar V., Bryxiová M. Research Institute of Crop Production, 161 06 Prague-Ruzyně, Czech Republic

Bacterial ring rot disease of potato, caused by Clavibacter michiganensis pv. sepedonicus (Cms) is a major concern of producers of seed potatoes in the all countries of the world. Current methods of detection of this pathogen rely primarily upon the use of serological procedures including an indirect fluorescent antibody stanining assay (IFAS) and enzyme-linked immunosorbent assay (ELISA).  Accurate identification of Cms is especially difficult when population levels are below 10,000 CFU per ml, of plant tissue or millilitre of plant sap. A further complication arises when potato samples contain other bacteria that exhibit cross-reactivity by IFAS and ELISA. Moreover, certain non-fluid variant of Cms that may occur in various natural populations exhibit antigenic variation and escape serological detection. In our tests, potato tubers from samples free of Cms were used.  Internal tissue was removed from tubers and homogenized. Cms strains were added to the homogenates to obtain final concentrations 104, 105, 10 6 and 10 7 CFU/ml. Bacterial extractions were prepared from homogenates. Of the 29 Cms tested, 22 strains belonged to fluid type, 3 to intermediate type and 4 to non-fluid type. Commercial monoclonal antibody Agdia (USA) again Cms was used to determination. Suitability of the monoclonal antibody for detecting various types of Cms strains was evaluated according to percentage of positive reactions. Using 22 fluid Cms strains, the percentage of positive reactions in potato tuber homogenates at concentrations 104, 105, 106 and 107 CFU/ml were 95, 91, 86 and 86 respectively. On the other hand, using 7 intermediate and no-fluid Cms strains, the percentage of positive reactions in potato tuber homogenates at concentrations 104, 105, 106 and 107 CFU/ml were 33-50, 33-50, 0-25, 0-50 respectively. The interesting thing about it is that the percentage of positive reaction in adequate Cms concentration in phosphate buffered saline was lower in comparison with Cms concentration in potato extracts.

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