Die Braunfäule der Kartoffel (Phytophthora infestans [Mont.] de Bary)

Losses from blight in the tubers comprise lasses caused by infection in the ground and lasses caused by infection at lifting favoured by the modern lifting technics. The amount of blight in tubers caused by infection before lifting depends on the time during which blight was actively sporing on the haulm. This time can be prolonged by chemical control, resistance of varieties or weather conditions unfavourable to the fungus, whereas biological or chemical haulm destruction reduces the amount of blight in tubers. If more than 0.1 per cent disease is present in the crop, the spraying tends to be ineffective against tuber blight. The fungicide is primarily effective against the incoming inoculum. These facts suggest the importance of forecast the onset of blight epidemics in due time. Before the wounds of tubers caused during harvest are closed with suberine in the outer cell layer, the infection with Phytophthora infestans induces a high percentage of bacterial rot. The methods for testing tuber resistance are discussed. The tuber-slice test according to L a p w o o d gives the best results. This method is based on the assessment of the development of surface mycelium after the fungus had grown through a slice of standard thickness.