Effects of crop rotation on the incidence of soil-borne pathogens and the consequences for potato production

This thesis describes the effects of various rotations on the growth pattern, yield and quality of potato and on the incidence of soil-borne pathogens, other than potato cyst nematodes ( Globodera spp.), associated with potato. These rotations differed in the frequency of potato and in the crops with which the potato crop was rotated.The effects of the rotations depended greatly on the soil type. Lower yields of potato in short rotations were mainly caused by Streptomyces spp. (causing netted scab), Rhizoctonia solani, Verticillium dahliae and, on sandy soil, also by root-knot nematodes (Meloidogyne hapla and M.chitwoodi). Rotation effects were indirectly influenced by the root-lesion nematodes Pratylenchus thornei and P.neglectus, and under special conditions, also by Colletotrichum coccodes. The susceptibility and tolerance of potato cultivars to these pathogens and synergistic interactions between the various pathogens largely determined the final yield depressions in the short rotations.