Potato cyst nematodes originate in the Andes in South America and were first found in North Germany in the first decades of the 20th century. Hence the name of the golden nematode Globodera rostochiensis, after Rostock, a city in Mecklenburg-West Pomerania in the North of Germany. The Gross Lüsewitz Potato Collection Genebank of the Leibniz Institute of Plant Genetics and Crop Plant Research is still there. A second introduction followed with the white potato cyst nematodes (Globodera pallida) found in Europe at the end of the 20th century.
Nowadays both pests are widely spread but not globally. Damage by nematodes is variety-dependent. Varieties differ in tolerance which is the yield loss caused by the same number of nematodes per g soil. Varieties also vary in resistance which is the reduction or increase in the existing population at harvest (Pf) compared to the population before planting (Pi). Higher soil temperatures, up to a certain maximum, positively influence the number of generations of nematodes per crop cycle, so also on the final nematode number Pf.
Nematodes are distinguished into free living ones that feed on what the environment offers and parasitic nematodes that feed on hosts such as Meloidogyne spp. causing root knots, hence called root-knot nematodes (RKN) and potato cyst nematodes (PCN). The latter has two sub-species: the golden and the white cyst nematode. The relative development rate, (RDR) of RKN is determined by its optimal temperature for the completion of one single life cycle: 25 days at 26 °C, a total of 650 day-degrees. Therefore, when the average soil temperature on a particular day is 26 °C, the RDR is 1/25 = 0.04. Below 10 °C and above 35 °C, the development rate is 0. RDR at intermediate temperatures is calculated through intrapolation. R. pallida’s optimum is at 21 °C and R. rostochiencis’ optimum for hatching of the eggs is at 24 °C, but both not with a steep decrease but with a gradual decrease around the optimum range. From egg to second stage juvenile takes 30 days for G. pallida and 40 days for G. Rostochiensis which is partly due to the lower hatching temperature optimum but not completely. Completing a cycle from egg to cyst takes 800 day-degrees for G. pallida and 900 for G. rostochiensis.
All three factors, hatching, development of a juvenile stage and completion of the life cycle are temperature-dependent. A 150-day growing season with an average soil temperature of 20 °C counts 3000 d°C allowing 3.3, 3.8, or 4.6 generations for the two cyst nematodes and for the root knot nematodes respectively. With a 2 °C temperature increase the temperature sum becomes 3300 d°C which allows 3.7 generations of G. rostochiensis, 4.1 of Potato cyst nematodes add half a life cycle per season when temperature rises 2 °C due to climate change or by e.g. growing the crop at lower altitudes where temperatures are higher G. pallida and 5.1 of the root-knot nematodes (Meloidogyne spp.). The projected increase in temperature leads to an additional generation of potato cyst nematodes in about half of the environments. In practically all environments there is room for another multiplication cycle of root knot nematodes. The expected damage is less than proportional to the number of generations, because with a higher temperature also the mortality increases as does predation by other pests and by fungal nematophagous diseases.
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