Modifications in the potato rhizosphere during infestations of Globodera rostochiensis and subsequent effects on the growth of Rhizoctonia solani Matthew Back & Peter Jenkinson & Thomas Deliopoulos & Patrick Haydock Accepted: 5 August 2010 / Published online: 6 September 2010 # KNPV 2010 Abstract Two controlled environment experiments were conducted to explore the hypothesis that invasion and damage caused to potato roots by the potato cyst nematode Globodera rostochiensis might result in quantitative or qualitative changes in the release of root exudates to subsequently affect the growth of Rhizoctonia solani (AG3) in the potato rhizosphere. The growth of five R. solani isolates was compared on media amended either with root exu- dates from G. rostochiensis-infested or uninfested potato (cv. Désirée) plants at different time intervals after the introduction of the nematodes. In Experiment 1, the growth of R. solani was higher on medium amended with potato root exudates from G. rosto- chiensis-infested compared to uninfested plants, col- lected 4, 6, 8 and 12 days after the G. rostochiensis treatments were administered. Similarly, in Experi- ment 2, R. solani isolates grew faster on medium amended with potato root exudates from G. rosto- chiensis-infested than uninfested plants. This trend was particularly pronounced at the 12-day collection. At this time, 49% of the G. rostochiensis juveniles in roots were found to belong to the juvenile moults J2 and J3, indicating that root exudates were modified during the earlier stages of juvenile invasion. Carbo- hydrate analysis of root exudates indicated signifi- cantly higher levels of sucrose in root exudates from G. rostochiensis-infested than uninfested plants, whereas no significant differences were found in total nitrogen content. The results are discussed to help elucidate the mechanism behind the disease complex found between G. rostochiensis and R. solani in previous field research. Keywords Black scurf . Disease complexes . Interactions . Potato cyst nematodes . Root exudates . Stem canker Introduction Rhizoctonia solani Kühn anastomosis group 3 (AG3) (teleomorph: Thanatephorus cucumeris (Frank) Donk) is a soil-borne fungus of potato (Solanum tuberosum L.) on which it causes stem and stolon canker and black scurf. It is frequently found in potato-growing areas worldwide, but infections and significant damage usually occur in areas with wet and cool soil conditions, such as in the UK, where it affects 60–80% of crops each year (Budge et al. 2002). Eur J Plant Pathol (2010) 128:459–471 DOI 10.1007/s10658-010-9673-2 M. Back (*) : T. Deliopoulos : P. Haydock Nematology and Entomology Group, Crop and Environment Research Centre, Harper Adams University College, Newport, Shropshire TF10 8NB, UK e-mail: mback@harper-adams.ac.uk P. Jenkinson Sellafield Ltd, Seascale, Cumbria CA20 1BG, UK