Effect of temperature on the interactions between beet cyst nematodes (Heterodera schachtii and Heterodera betae) and sugar beet

Climate change is expected to cause a mean annual temperature increase in Germany of 2 °C by 2050 and up to 4 °C by 2100. This is likely to have effects on crop development and pathogen development as well. For this Ph.D. thesis, experiments were conducted to investigate the effect of increasing temperatures on the beet cyst nematodes Heterodera schachtii and Heterodera betae and thus study the changes of their interaction with their host plant the sugar beet (Beta vulgaris subsp.). Differences in hatch between the beet cyst nematode species were assessed at constant temperatures in incubators as well as simulated temperature conditions set to be 4 °C higher than the standard temperature regime. The optimal temperatures for hatch were found to be different for both cyst nematode species. The optimal temperature range for hatching of H. schachtii was found to be between 15 and 30 °C and for H. betae between 20 and 30 °C. Emergence of juveniles of both beet cyst nematode species began at 5 °C, however in very low percentages. For both beet cyst nematode species no significant differences were found in the final cumulative hatch percentages when comparing the standard temperature regime with the by 4°C increased temperature regime. In the climate chambers, the influence of temperature on the interspecific competition between both beet cyst nematode species was studied. Both beet cyst nematode species performed better at higher temperatures. But there were no clear indications that under competition one of the two species will profit more from higher temperatures under the predicted climate change. In conclusion, the damage done by cyst nematodes in sugar beet is expected to increase with global warming. H. schachtii and H. betae are likely to continue to cause damages. But in competition, neither of the two species will profit more from rising temperatures compared to the other. The effect of experimental soil warming on H. schachtii population development and sugar beet performance was assessed for sugar beet cultivars that were susceptible, tolerant or resistant to H. schachtii. In this study, soil heating lead to a significant increase in the final number of recovered cysts on the tolerant cultivar and susceptible cultivar. The resistant cultivar did not allow nematode reproduction at all. Therefore no effect of soil heating could be detected. Plant-nematode interaction varies greatly depending on the cultivar. Thus cultivar choice is an important element when trying to prevent nematode infestation or controlling nematode populations in the field. In case of high nematode population densities and with the expected increasing soil temperatures, planting nematode-resistant cultivars will become even more important in the future, as an effective tool to reduce nematode populations and prevent damages.