Field damage in potato by lesion nematode Pratylenchus penetrans, its association with tuber symptoms and its survival in storage
AbstractSoil samples from an area of depressed growth in a potato (Solanum tuberosum) cv. Saturna field in Grue, eastern Norway, yielded large numbers of root lesion nematodes, Pratylenchus penetrans. The yield of potatoes was reduced by 50% in the affected area of the field. Transect-sampling showed plant growth to be negatively correlated with densities of P. penetrans and suggested a damage threshold of potato to the nematode of 100 specimens per 250 g of soil. Common scab (Streptomyces scabies) occurred frequently in the affected area. Pratylenchus penetrans was present in roots, underground stems, stolons and tubers. In tubers, nematodes were detected inside cross-lesions typical of common scab, and occurred also in the outermost 0.5 mm of tissue associated with such lesions. On potato cv. Saturna grown in a greenhouse, P. penetrans alone induced tuber lesions similar to those of common scab. Also, the combined inoculation of the bacterium and the nematode seemed to enhance symptom expression. Pratylenchus penetrans survives storage of potatoes, and new infections may develop from infected tubers used as seed. Hence, potato tubers do appear to be an important means for the spread of P. penetrans to new areas.