Een zwakke stam van het virus van de grofmozaïekziekte

Summary In the Netherlands potatoes of the variety Industrie are being cultivated which are free from any virus disease. They have dark green leaves and are called „donkere Industrie”. Besides these „donkere Industrie” are cultivated potatoes of the same varity which have a paler green foliage and which are called „lichte Industrie”. It is evident that the pale colour of „lichte Industrie” is caused by a virus. This virus turned out to be a feeble strain of the virus of „grof moza?ek” (mild-mosaic) and to bring about a rather entire immunity to this virus.      

Bestaat er een verband tusschen het voorkomen van black heart en het optreden van virusziekten bij den aardappel?

Summary Biourge andSokal have claimed: firstly: Black heart is not caused by lack of oxygen, followed by suffocation of central part of the tuber, but it results from attack byBacillus mesentericus vulgatus;Flugge) andBacillus mesentericus ruber (Globig); Secondly: Tubers suffering from black heart develop plants suffering from the diseases, which have been ascribed to viruses. Therefore it is not necessary to suppose the existance of viruses. This type of disease is caused by the bacilli mentioned. Sanitation of the plants can be performed by keeping the tubers during 48 hours at 42 centigrades. The tubers withstanding this heating without turning black develop virus-free plants. The present author however has, in controlling experimentally the work of the writers mentioned above, not been able to detect any relation between the occurrence of black heart in the tubers and of viroses in the sprouts. Sensibility for black heart proved to be more dependent on the climate and the soil, than on hereditary characters of the potato variety. Between the melanine-value (as aimed byHaehn) and the intensity of black heart, thus far no correlation has been found by the present author.     

Aan de Lezers van het «Tijdschrift over Plantenziekten»

Aan de Lezers van het „Tijdschrift over Plantensiekten”.     

Roepke's werk op het gebied van de toegepaste entomologie voor het voormalig Nederlandsch Oost Indië

Ohne Zusammenfassung     

Over de vatbaarheid van niet-kruisbloemige planten voor het zoösporangium-stadium vanPlasmodiophora brassicae Woron

Samenvatting en bespreking Een vijftiental plantensoorten werd onderzocht op vatbaarheid voor het zoösporangium-stadium vanP. brassicae. Hiervan werdenTrifolium pratense, Reseda odorata enLolium perenne in zeer geringe mate, enPapaver rhoeas iets sterker aangetast. De mate van aantasting van deze laatste was echter nog aanzienlijk minder dan van als vergelijkingsobject gebruikte bloemkoolplantjes. Gezien deze resultaten is het niet waarschijnlijk, dat niet-cruciferen enigermate kunnen bijdragen tot de instandhouding of vermeerdering van de schimmel bij afwezigheid van kruisbloemigen. Evenmin is er reden te veronderstellen, dat niet-cruciferen als vangplanten voor het uitroeien van de rustsporen van groot practisch belang kunnen zijn.Summary Webb's (1949) discovery of zoosporangia ofP. brassicae in non-crucifers raises the question of further means of multiplication and survival in the soil (MacFarlane, 1952). Perhaps the fungus can maintain itself in successive generations of zoosporangia in root hairs of these plants. From there it might in turn infect crucifers and produce a fresh crop of resting spores. This must be kept in mind when considering the possibility of eradicating the fungus from the soil by growing non-crucifers which stimulate the resting spores to germinate. If survival in root hairs were important, plants for this purpose would need to resist the zoosporangial stage as well as stimulate spore germination.In the present study a number of non-crucifers was tested for susceptibility to the zoosporangial stage by a method already described (Kole, 1955). In addition, the rate of infection of susceptible non-crucifers was compared with that of cabbage grown under the same conditions. Of seven non-crucifers, not tested before, onlyTrifolium pratense became infected.MacFaralane's findings of non-cruciferous hosts were confirmed forPapaver rhoeas, Reseda odorata andLolium perenne (Table 1). In all the susceptible non-crucifers exceptPapaver rhoeas, infection was very sligth. There were more infections onPapaver rhoeas than on the other non-crucifers but fewer than on cabbage, which was heavily infected. On the basis of these results it is not thought that the occurrence of non-cruciferous hosts ofP. brassicae will generally be of great practical importance.     

Een oriënterend onderzoek naar het voorkomen van en de schade veroorzaakt door het havercystenaaltje (Heterodera avenae = H. major) in 1955

Samenvatting Op vele bedrijven, waar een sterke rotatie van granen in het bouwplan is opgenomen, kan het havercystenaaltjes veelvuldig moeheidsverschijnselen in haver veroorzaken. Ook op bedrijven, waar dit gewas geen afwijkingen in de groei vertoont, komt het aaltje, zij het in geringe concentraties, algemeen voor. Tussen de besmettingsgraad van de grond en de schade aan het gewas bestaat een zeker verband. Dit verbank kan sterk beïnvloed worden door verschillende bijkomende factoren, waaronder de watervoorziening van der planten een belangrijke rol speelt.Het is nog niet duidelijk in hoeverre de techniek van het grondmonsteronderzoek gewijzigd dient te worden om te voorkomen, dat de levende inhoud van de cysten terugloopt.Summary The cereal root eelworm has become a serious pest in oats in some parts of the Netherlands, especially on light, sandy soils.In March and April 1955 1400 soil samples were collected from farms where the occurrence of the nematode was to be expected.In two different areas the degree of infestation was 78 and 96% of the total of fields under investigation. These figures indicate that the concerning farms were generally infested, but they do not represent the mean situation of the area.During the growing season each oat crop was examined for symptoms of the disease. The data collected were compared afterwards with the degree of infestation. There proved to be a positive correlation between the degree of infestation of the soil and the damage to the crop (tables 1 en 2). Several circumstances influence this correlation, among which the water supply of the plants seems to be a very important one.Cyst populations were identified by morphological characters to separate them from the clover root eelworm,Heterodera trifolii (Goffart, 1936), which was also present in 6,5% of the samples in one, and in 32% of the samples in the other area.The larvae in the cysts ofH. avenae evidently do not stand dry preservation, which is in accordance with recent experience in England (2).Dry preservation inplastic cavity slides for 1–3 weeks resulted in a decrease of viable cysts and larvae of 52%. A more suitable technique for collecting and handlingH. avenae in studied for further work.Het onderzoek werd verricht in samenwerking met de Rijkslandbouwconsulenten te Zutfen en Horst (L.) en het kantoor van de Plantenziektekundige Dienst te Doetinchem.