Impact of the root-knot nematode, Meloidogyne incognita, on potato during two different growing seasons

An investigation was conducted in southern Italy to ascertain the effect of the root-knot nematode, Meloidogyne incognita, on potato during the autumn and spring growing seasons. The experiments were conducted in microplots containing 25.6 dm3 soil infested with initial population densities (Pi) of 0, 0.06, 0.125, 0.25, 0.5, 1, 2, 4, 8, 16, 32, 64, 128 or 256 eggs and juveniles of the nematode/cm3. Plant height was monitored during the growing seasons and top weights of plants, tuber yields and nematode population densities were recorded at harvest. The effect of the nematode on growth and yield of potato was severe during the autumn season but almost negligible during the spring season. A tolerance limit of potato to M. incognita of 1.2 eggs and juveniles/cm3 soil was only estimated for the autumn season, when a maximum tuber yield loss of 80% occurred at Pi ≥ 128 eggs and juveniles/cm3 soil. Plant fresh top weight and plant height had patterns similar to that of tuber yield. The number of tubers was not significantly affected by the nematode but the average weight per tuber was reduced at Pi ≥ 64 eggs and juveniles/cm3 soil during the autumn season and at Pi of 128 eggs and juveniles/cm3 soil during the spring season. The post-harvest soil population density of M. incognita declined strongly in the autumn season and increased slightly in the spring season, when a maximum reproduction rate of 9.1-fold was observed. At harvest, tubers did not show symptoms of nematode attack. The nematode was not found in the tubers harvested in December but symptoms of nematode attack and many nematodes inside the tubers collected in June became obvious 4-5 months after harvest.