Waarnemingen betreffende Ditylenchus radicicola (Greeff, 1872) Filipjev, 1936

Summary On account of recent records ofDitylenchus radicicola (Greeff, 1872)Filipjev, 1936 in Dutch meadows, a study was made of its biology. Literature data were summarized.The eelworm attacks the roots of Gramineae and causes spiralshaped galls, which may contain up to 60 adults and some thousands of eggs and larvae each. Young larvae may actively hatch in water from whole, undecayed galls at temperatures around 17°C (Graph. 1). Root exudate of host plants did not stimulate the hatching process. The first larval stage is infective and may penetrate young root tips and also young galls (Fig. 1); it can withstand 2 month desiccation and also desinfection in a solution of an organic mercury compound. The host plant influences the number and size of the root galls (Graph. 2). Fig. 2 shows the anatomy of a young gall.The parasite is only found in grasses in this country and damage has not yet been found. Rye, wheat, barley and oats proved to be susceptible in inoculation trials; 17 plant species have been mentioned as natural hosts in different countries now and 3 are only found susceptible in inoculation trials.     

Een nieuwe methode voor bepaling van de vatbaarheid van klaverplanten voor het stengelaaltje (Ditylenchus dipsaci (Kuhn) Filipjev)

Summary For breeding purposes a new method of artificial infection was developed, which seems of great promise and makes possible work on a large scale. Clover is sown in boxes of, sterilised soil. After emergence the seedlings are sprayed with a concentrated suspension of eelworms in water and placed in a room at 15–20°C, with high air humidity. Two weeks after inoculation the symptoms are clearly visible.     

Verschillende belangrijke punten voor het pootgoedvraagstuk bij aardappelen,in het bijzonder ook de rol,die de afdeelingen (der landbouwmaatschappijen) daarbij kunnen vervullen

European Journal of Plant Pathology -     

De vetvlekkenziekte,een voor Nederland nieuwe ziekte bij bruine boonen (Phaseolus Vulgaris)

Laboratorium voor Microbiologie.     

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 oorzaak van het optreden van dwergmozaiekzieke aardappelplanten (stekelkoppen)

Conclusie Het dwergmozaiek (stekelkop) ontstaat door een combinatie van het virus van grofmozaiekziekte en het virus van stippelstreepziekte.Conclusion A type of curly dwarf can be produced by a combination of the virus of roughmosaic and the virus of stipple-streak.     

Pyemotes herfsi (Oudemans, 1936) as causative agent of another mass dermatitis in Europe (Acari, Pyemotidae).

The authors describe new cases of human dermatitis caused by Pyemotes herfsi occurring in the food mixing shed for the farrowing house in the piggery at a farm in the destrict of Olomouc, where seven persons handling feedstuff were infected. The disease became manifest as a papular rash, appearing particularly on the back, and all over the body except on the hands and face. When the afflicted person discontinued work in the feed mixing shed, the rash disappeared quickly. The mites were found in the granular dust accumulated in the loft above the food mixing shed. The initial host (insects) could not be identified. After cleaning and disinsecting the contaminated premises with Metation E 50 the workers were free from any symptoms. The mites of the genus Pyemotes, particularly the species P. herfsi (Oudemans, 1936) are little known, but probably frequent causative agents of human dermatitides.