Vier jaren voortgezet onderzoek over de schurft van appel en peer

European Journal of Plant Pathology -     

Het toezicht op de constantheid van samenstelling van vruchtboomcarbolineum

Voordracht gehouden tijdens de Landbouwweek te Wageningen 3 t/m 7 5uli 1933     

De Invloed van de Uitwendige Omstandigheden Bij Het Optreden van Boonenziekten

Summary The influence of environmental conditions on diseases of the bean (Phaseolus) were studied last summer on the field and at the laboratory. The diseases due to deficiencies of anorganic matter were accompanied by distinct symptoms during June and July, but later on could scarcely be recognized. The dry and warm conditions during both these months were the cause of great damage due to red spider and plant lice. The virus diseases which are transmitted by lastnamed insects, were very much spread, in particular„curlmosaic” (Phaseolus virus 1), „yellow mosaic” or „steengrauw” (Phaseolus virus 2?). „Stipple-streak” (Nicotiana virus 11?) was partly masked during the heat season, but showed in August characteristic redbrown „ringspot” on the pods. This virus disease has wrongly been taken for a bacterial blight. The haloblight, however, is seedborne and gave rise to a heavy attack e.g. on „Ceka” beans in August. In June and July the disease could hardly be discovered in the fields. Further some „rust”- and „foot” diseases have been studied, which are often troubled withUromyces appendiculatus andColletotrichum Lindemuthianum. It was shown thatAscochyta Boltshauseri andAscochyta phaseolorum, both seedborne diseases, caused at first a foot- and stem-anthracnose, which was of little importance in midsummer; but in August the disease spread over the leaves and pods, causing brownish spots that flow together and give a reduction of quality and in yield. The footrots due to Fusarium sp., Sclerotinia sclerotiorum and Botrytis cinerea eem also to increase during cool moist weather.

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Laboratorium voor Mycologie en Aardappelonderzoek, Dec. ’41.     

De infectie van opgeslagen aardappelknollen door phytophthora infestans (Mont.) de by

Summary Wet steamed clay-soil, contaminated with conidia, has been stored during a fortnight in a closed petridish at a temperature of about 16°C.Tubers of the variety Bintje were brought into contact with this wet clay in a glass dish and placed at about 16,5°C.After 9 days a rich growth of sporulating Phytophthora became visible on the clay adhering to the tubers; at that moment tuberlesions were not yet visible, though probably a light infection had taken place; 3 days later the first lesions could be observed.In a second experiment potatotubers (var. Bintje) were inoculated with Phytophthora and one day later brought in an Artificial Clamp. The temperature was first about 16°C, afterwards 18,5°C, the relative airhumidity was about 75%.After 22 days the sprouts of the tubers were to be removed; 17 days later new sprouts had developed. At that moment the fungus sporulated out of several tubers through lenticels and little wounds. The sporulating growths were made up of about 10 conidiophores, which had produced 40 to 50 conidia; only one consisted of a great many conidiophores. Sporulating Phytophthora also was visible around the base and at the top of the sprouts.These experiments have proved that under wet conditions (as it occurs often in potatoclamps) stored potatotubers from a diseased crop are infected with Phytophthora by conidia which are present in the adhering clay. The fungus maintains its infectingpower under these conditions for at least a forthnight. At the places, where the fungus invades the tubers, sporulations may appear on the adhering soil, by which new contaminations and new infections may take place. Contaminations also take place with conidia, produced by conidiophores, grown out through lenticels, little wounds and perhaps through the buds from infected tubers. So there may be some spread from infected tubers to sound ones in storage.     

Wisselbouw van aardappelrassen als bestrijdingsmiddel tegen schurft

Summary Four potato varieties were grown in a frame filled with soil, heavily infected with scab. For six successive years each variety was grown on the same plot. After these six years two potato varieties, Bintje and Eigenheimer, were cultivated on all plots. The attack and type of scab varied according to the susceptibility of the potatoes grown during the preceding period. Where Jubel was cultivated for six years the attack was least, where Bintje had been grown successively much superficial scab occurred, in the Eigenheimer-plot many deep scab lesions were found. Rotation with potato varieties resistant to scab may have good results if the disease occurs on later grown susceptible potato varieties. These results agree with the facts found by different authors (1, 5, 7, 8) viz. that different types of scab on the same potato are due to special races of Actinomyces, that the susceptibility of the different potato varieties to these Actinomycesraces is not the same and that the virulence of the scab organisms is increased through development on the living growing potato. In verband met de nog weinig uitgewerkte systematiek van de Actinomyceten is geen verschil tussen rassen en soorten van Actinomyces gemaakt en wordt in dit artikel alleen van rassen gesproken.