title: The interaction between potato cyst nematodes and <i>Rhizoctonia solani</i> diseases in potatoes
Creators: name: Back, Matthew Alan
Publisher: name: The Open University
Year: 2004

description: The soil-borne pathogen <i>Rhizoctonia solani</i> and the potato cyst nematode <i>Globodera rostochiensis</i> are detrimental to the growth and productivity of potato crops in the UK. Previous work has shown that plant parasitic nematodes and fungal pathogens can occasionally interact synergistically to form destructive disease complexes. Furthermore, there is some evidence to suggest that an interaction might exist between <i>G. rostochiensis</i> and <i>R. solani</i> on potato. <br><br>In order to investigate interactions between <i>G. rostochiensis</i> and <i>R. solani</i>, a series of glasshouse and field experiments were undertaken (2000-2001). In field experiments, plots infested with similar population densities of <i>G. rostochiensis</i> were either uninoculated or inoculated with <i>R. solani</i>. A series of potato plant harvests were undertaken to investigate the effects of nematode infestation on the incidence and severity of <i>R. solani</i> diseases and the associated development of plants. In both experiments, a positive relationship was found between the density of <i>G. rostochiensis</i> juveniles present in potato roots and the incidence of stolons infected by <i>R. solani</i>, 6 weeks after planting. Weaker relationships were found between <i>G. rostochiensis</i> densities and stolon infections at 4 and 8 weeks after planting. In addition, a number of relationships were found between <i>G. rostochiensis</i> infestations and other <i>R. solani</i> disease symptoms, although these were less consistent across the harvest dates. In 2002, the experimental plot design was modified to further investigate the effect of <i>G. rostochiensis</i> on black scurf disease caused by <i>R. solani</i>. However, no relationship was observed between <i>G. rostochiensis</i> infestations and the later development of black scurf on daughter tubers. <br><br>The glasshouse experiments of this project did not show a direct interaction between <i>G. rostochiensis</i> and <i>R. solani</i> diseases. However, both glasshouse experiments were limited by the method used to infest potting medium with <i>G. rostochiensis</i>. <br><br>On the basis of results obtained from the field experiment, two controlled environment experiments (2002) were undertaken to investigate the growth rate of <i>R. solani</i> in response to root leachates from potato plants uninfested or infested with <i>G. rostochiensis</i>, at different time intervals after the introduction of nematodes. In addition, the concentration of carbohydrates and nitrogen was determined from the root leachate samples. In both experiments, <i>R. solani</i> isolates were found to have a significantly higher radial growth on media amended with root leachates from <i>G. rostochiensis</i> plants compared to uninfested plants at 12 days after the introduction of nematode treatments. Furthermore, a higher sucrose concentration was detected in root leachates from <i>G. rostochiensis</i> infested plants compared to root leachates from uninfested plants. Since exogenous carbohydrates are known to influence the growth and attraction of <i>R. solani</i>, these results may go some way to explain the interaction found.