De overbrenging van een virusziekte van zure kers op komkommer

Summary Cucumber seedlings were infected with a virus from sour cherry by rubbing the cotyledons with sap from young sour cherry leaves, showing shock effect symptoms of a virus infection (probably necrotic ringspot). The symptoms on cucumber consisted of necrosis of vegetation point, yellow spots in the leaves and rosette formation, thus showing the resemblance of this infection to the oneMoore, Boyle andKeitt effected in cucumber by using a mixture of necrotic ringspot and yellows virus.     

Cnephasia longana,een beschadiger van de scheuttoppen van fruitgewassen

In the Netherlands, the polyphagous larvae ofCnephasia longana Haworth occur locally on apple and pear trees, damaging the growing shoot-tips. They are also observed on red currant bushes, strawberry, beet, clover, lucerne and creeping thistle. A useful degree of control has been obtained with organo-phosphorus sprays.     

Onderzoekingen over een virusziekte bij stoppelknollen (Brassica Rapa var.Rapifera)1)

European Journal of Plant Pathology - Beschreven worden de eigenschappen van een virus, behorende tot de groep van “turnip virus 1”, dat in 1949 ernstige schade in stoppelknollen...     

Kurkwortel verschijnselen van tomaat,veroorzaakt door een steriel mycelium. II

Ohne Zusammenfassung

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With a summary: Corky root of tomato caused by a sterile mycelium. II

     

Bij het begin van de een en zestigste jaargang

Ohne Zusammenfassung     

Enkele waarnemingen over het opreden van de verwelkingsiekte bij luzerne in Zeeland in 1957

Summary Some observations have been made on lucerne wilt disease during the growing season in 1957, and in experimental inoculation tests in a glasshouse in 1958. In the province of Zeeland the disease does harm to the crop and prevents many farmers from keeping their crops longer than two years.In a survey data have been collected on soil type, preceding crops, green manuring and manuring with stable dung, pH, structure and weeds. No correlations between these factors and the degree of attack by the disease could be proved, except that on heavy soils the disease was less severe than on lighter soils (as a mean of all observations).Development of the disease is facilitated by damage caused by mechanical equipment to the crop. Damage to the crown of the plants should be avoided as much as possible. The disease is distributed extensively after frequent mowing. On attacked leaves left behind on the mowed stalks, and on decayed leaves dropped to the soil, masses of spores ofVerticillium albo-atrum are produced, which form a potential source of infection in a weakened crop.It seems that the disease is more air-borne than soil-borne, since one year old crops are seldom attacked.From attacked lucerne plants in the field the following fungi have been isolated:Verticillium albo-atrum Reinke & Berth.,Gliocladium roseum Bain andFusarium avenaceum (Fr.) Sacc. (table 1).Isolations have been made from 50 different species of weeds, out of which the following fungi were obtained:Verticillium albo-atrum Reinke & Berth. fromCapsella bursa-pastoris Med. andPlantago major L.,V. dahliae Kleb. fromPrunella vulgaris L.,Capsella bursa-pastoris Med. andThlaspi arvense L., andV. lecanii (Zimm.) Viegas fromPlantago major L.In inoculation experiments with all these isolates, in roots, stalks and on cut plants of lucerne, onlyV. albo-atrum, both from lucerne and weeds, andV. lecanii proved to be able to cause wilting of leaves and stalks. WithGliocladium, Fusarium andVerticillium dahliae no such symptoms could be obtained. The results were the same whatever method of inoculation was used.     

Het stippelstreep van de boon (Phaseolus vulgaris), een ziekte veroorzaakt door een virus,dat in de grond overblijft

Summary It has been shown in a field experiment that stipplestreak — a virus disease of haricot beans (Phaseolus vulgaris) — is carried by the soil. Keeping the infected soil at 100°C. for 30 minutes destroys the virus.Young haricot bean plants may become infected naturally with the stipplestreak virus within the first week after sowing the seeds in infected soil. The stipple-streak symptoms, however, do not appear until considerably later; for example, in 1947, they did not appear until about six weeks after the seedlings had been transferred (one week after seed sowing) from infected to non-infected soil.According toHubbeling, whose experimental results it was possible to confirm, the properties of the virus in freshly expressed sap are: — thermal inactivation point, between 85° and 90°C; solution end point, between 10^–5 and 10^–6. The virus resists drying out.The virus causes local necrotic spots — often in the form of concentric rings —on the leaves of tobacco (Nicotiana tabacum).Gaarne wordt ook op deze plaats dank betuigd aan de heren A. J. van Velzen, Assistent bij de Rijkstuinbouwvoorlichtingsdienst en Jac. van der Meer, tuinder, beiden te Roelofarendsveen voor hun zorg besteed aan het koken van de grond en aan het proefveld aldaar.Onderzoek, verricht voor de afd. Tuinbouwkundig Onderzoek van de Directie van de Tuinbouw.     

De invloed van enige virussen op de concentraties van organische zuren in een aantal planten

Samenvatting In dit onderzoek werden de concentraties van organische zuren in gezonde en in even oude, met virus geïnfecteerde planten vergeleken. Deze proefplanten warenPhysalis floridana, Nicotiana tabacum var. White Burley enLycopersicum esculentum var. Ailsa Gray. Partijen van 40 of 60 planten werden mechanisch geïnoculeerd, respectievelijk met X-virus, Y-virus, tabaksmozaïekvirus en een virus, dat rozetziektesymptomen op de kers veroorzaakt. Bovendien werd bladrolvirus, overgebracht doorMyzus persicae, bijPhysalis en tomaat in het onderzoek betrokken.Zowel op de dag van de inoculatie als 7, 14 en 21 dagen later werden 20 gezonde planten en 20 exemplaren van elke genoemde partij geoogst. Elk monster werd met water geëxtraheerd. Na zuivering van het extract door een sterke kationwisselaar Imac C 12 en concentratie in vacuo werden de organische zuren met behulp van silicagelzuilen en mengsels van chloroform en n-butanol als solvents kwantitatief bepaald. Twee dimensionale papierchromatografie maakte verificatie van de identificatie van de in de extracten voorkomende zuren mogelijk.Behoudens een enkele uitzondering werd in het algemeen gevonden, dat de zieke planten hogere zuurgehalten bezitten dan de gezonde. Het wordt waarschijnlijk geacht, dat door de virusinfectie het evenwicht tussen de fotosynthese, de ademhaling en de eiwitsynthese zodanig verschuift, dat het gehalte van de organische zuren, speciaal dat van appel- en citroenzuur, verhoogd wordt.Summary A number of publications, concerning special aspects of the relationship between virus synthesis and the metabolism of organic acids, showed a reciprocal influence. However a more general investigation into the influence of the virus infection on the changes in organic acids seemed necessary.In the present paper the concentrations of organic acids in healthy plants and in those of the same age, infected with virus, are compared. For this purpose plants ofPhysalis floridana, Nicotiana tabacum var. White Burley andLycopersicum esculentum var. Ailsa Gray were used. Groups of 40 or 60 plants were inoculated with potato virus X, potato virus Y, tobacco mosaic virus and a virus, causing symptoms of rozet ziekte in cherry respectively. The potato leaf roll virus, transmitted byMyzus persicae, was used withPhysalis and tomato.On the day of inoculation as well as 7, 14 and 21 days later 20 healthy plants and 20 specimen of each group, above mentioned, were harvested. These samples were boiled for five minutes in an amount of water of twice the fresh weight. After mixing, each suspension obtained was subjected to 10,000 atm. in a hydraulic press, the sap then centrifuged (8000 r.p.m. during 10 min.) and the residue washed once. The combined supernatants were percolated through a strong cation-exchanger Imac C 12 (columns of 30×1.2 cm). The effluent contained the organic acids and the carbohydrates. Further purification appeared not to be necessary. The solution was concentrated in vacuo at 40–50°C and dried in a warm stream of air.The organic acids in the dried preparations were analyzed according to the method ofBulen, Varner & Burrell (1952) on silicagel columns of 4 grams, the preparation of which is described byNijkamp (1954). AsBulen et al. worked with columns of 8 grams, we used proportional amounts of solvent mixtures of chloroform and n-butanol, recommended in their publications. After placing the column on a fraction collector, the fractions were titrated against 0.01 n NaOH, using bromothymolblue as an indicator.Although each organic acid leaves the column at a definite fraction-number we verified the identifications of the acids by means of paper chromatography (Wolfgang, 1957) on Ederol-202 filter paper. A mixture of 80 volumes of 96% ethanol, 4 vol. of ammonia and 16 vol. of water as the first solvent and a mixture of 77 vol. of n-butanol, 12 vol. of formic acid and 11 vol. of water as the second solvent were used. After dipping the paper in a mixture of 16 ml aniline, 5 g glucose, 30 ml 96% ethanol and 470 ml light petroleum (b.p. 40–60°C) and heating for 15 min. at 120°C the acids became visible as brown spots on a white background. Especially oxalic, malic and citric acids were demonstrated on the papers.In general the tables show that during the development of the plants the content of organic acids, particularly of the oxalic, malic and citric acids, is lower in normal plants than in diseased ones. ThePhysalis plants, infected with the viruses X and Y and the tomatoes, inoculated with leaf roll virus and virus X are an exception to this. Their contents of organic acids being the same during the first week after the virus-inoculation as those of normal plants. The higher concentrations of the acids in tobacco could be shown very clearly already one week after the infection, whereas the symptoms were not yet visible. The same occurs in the case of tomatoes infected with virus Y, tobacco mosaic virus and the cherry virus.Investigations by several authors have shown an increased respiration activity and a decrease in photosynthesis. It is assumed that the substrate for the synthesis of organic acids will be present at a lower rate. As the synthesis of proteins would be decreased, a higher content of organic acids would result.