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.