New Disease Reports
New Disease Reports (2004) 9, 17.
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First report of Rhizoctonia solani anastomosis group 5 (AG5) on couch grass in Britain

J.W. Woodhall 1 and A.K. Lees 2*

*alees@scri.sari.ac.uk

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Accepted: 19 Mar 2004

Rhizoctonia solani is a significant pathogen of potatoes, causing stem canker and black scurf, resulting in both quantitative and qualitative damage to the potato crop. Isolates of R. solani can be assigned to one of the 13 known anastomosis groups (AG) (Carling et al., 2002).

In 2002, growers were asked to submit potato samples exhibiting rhizoctonia disease symptoms, as part of a project investigating the disease in potato crops. Couch grass (Agropyron repens) was present in several of the samples received and Rhizoctonia solani was isolated from a couch grass stem base originating from Shropshire. The isolate was designated T1 and was assigned to an AG by both observation of hyphal fusion and DNA sequencing. Perfect hyphal fusion was observed between T1 and two other isolates of AG5. No fusion was observed between T1 and isolates representing seven other AGs. Blast searches (Altschul et al., 1990) revealed that the rDNA ITS region of T1 [AY545999] was at least 99% identical to that of other AG5 isolates on the GenBank database.

Five, 10 mm plugs of isolate T1 cultured on potato dextrose agar, were used to inoculate soil into which either seed of A. repens or seed potatoes were planted. After 6 weeks, brown lesions were observed on couch grass roots and stem bases (Fig. 1). Large, brown lesions were observed on potato stems (Fig. 2). Re-isolation of the fungus from couch grass and potato satisfied Koch's postulates.

To our knowledge, this is the first report of R. solani infecting couch grass in Britain and more specifically, the presence of R. solani AG5 in Britain. As shown in this report and elsewhere (Bandy et al., 1984), R. solani AG5 can cause significant damage to potatoes. Infected couch grass may be an additional source of Rhizoctonia inoculum and may increase survival of inoculum through successive crop rotations. The ability of couch grass to harbour this pathogen may therefore be an important consideration in controlling rhizoctonia disease.

Figure1+
Figure 1: (Left). Potato stems (cv. Desiree) showing lesions caused by infection with R. solani AG5
Figure 1: (Left). Potato stems (cv. Desiree) showing lesions caused by infection with R. solani AG5
Figure2+
Figure 2: (Right) Couch grass stem infected with R. solani AG5.
Figure 2: (Right) Couch grass stem infected with R. solani AG5.

Acknowledgements

J. Woodhall is in receipt of a studentship funded by Harper-Adams University College and Bayer CropScience.

References

  1. Altschul SF, Gish W, Miller W, Myers EW, Lipman DJ, 1990. Basic local alignment search tool. Journal of Molecular Biology 215, 403-410.
  2. Bandy BP, Zanzinger DH, Tavantzis SM, 1984. Isolation of anastomosis group 5 of Rhizoctonia solani from potato field soils in Maine. Phytopathology 74, 1220-4.
  3. Carling DE, Kuninaga S, Brainard KA, 2002. Hyphal anastomosis reactions, rDNA internal transcribed spacer sequences, and virulence levels among subsets of Rhizoctonia solani anastomosis group 2 (AG2) and AG-BI. Phytopathology 92, 43-50.
This report was formally published in Plant Pathology

©2004 The Authors