Biological diversity of Rhizoctonia solani (AG‐3) in a northern potato‐cultivation environment in Finland

Abstract

A total of 119 isolates of Rhizoctonia were collected from stem canker lesions, stolon and root lesions, hymenia on stems, or from black scurf on tubers of potato plants ( Solanum tuberosum ) in Finland (latitudes 60 -67 ° N). All isolates except three belonged to anastomosis group 3 (AG-3) of R. solani , as determined by phylogenetic analysis of the internal transcribed spacer sequences (ITS1 and ITS2) of ribosomal RNA (rRNA) genes. Sensitivity of the 119 isolates to the fungicide flutolanil was tested in vitro (EC 50 values 0·14-0·75 µ g active ingredient mL − 1 ). The isolates also varied considerably in growth rate (5·1-14·8 mm day). The severity of disease caused by 99 isolates was determined based on the proportion of potato sprouts affected by lesions, discoloration or death, which was c . 1 -60%. Only two isolates that were able to cause severe symptoms showed particularly low sensitivity to the fungicide and rapid growth rate. One isolate each of anastomosis groups AG-2-1 and AG-5 and an unknown, binucleate Rhizoctonia sp. were detected. The AG-5 isolate and the binucleate isolate caused mild symptoms on potato sprouts, whereas the AG-2-1 isolate was not pathogenic. Taken together, AG-3 of R. solani was the predominant causal agent of the stem canker and black scurf diseases of potato in Finland and showed considerable variability in disease severity, fungicide sensitivity and growth rate in vitro .

Evolutionary Diversification Indicated by Compensatory Base Changes in ITS2 Secondary Structures in a Complex Fungal Species, Rhizoctonia solani

“…Direct sequencing of the ITS1-5.8S-ITS2 region amplified from the 503 strains by PCR revealed 73 distinguishable sequences (Supplementary Table 1), of which 26 were reported in a previous study (Lehtonen et al 2008). These predominant haplotype sequences (see below) revealed by direct sequencing of PCR products were compared with the ITS sequences of 80 strains of AG-3 from other countries, and the ITS sequences of the AG reference strains (Supplementary Table 1) by phylogenetic analysis.…”

“…Of the 503 strains isolated, the ITS sequences of 106 strains and also the virulence, fungicide tolerance and growth rate of 98 strains have been reported (Lehtonen et al 2008). The remaining strains were characterized for ITS sequences in this study.…”

“…The binucleate Rhizoctonia strain R92 of an unknown species (Lehtonen et al 2008) had a slightly different motif (CGGU) 5 0 to the apex of helix III (Fig. 4).…”

“…Strains of R. solani were collected from 281 potato fields in 53 communes distributed throughout Finland (latitude 60°-65°N) in 2002(Lehtonen et al 2008. The numbers of strains collected from different regions were proportional to the acreage of potato production from the total potato production area in Finland.…”

“…ITS1 and ITS2 regions, including the 5.8S rRNA gene, were amplified by polymerase chain reaction (PCR) using the universal ITS-1 and ITS-4 primers that anneal to the flanking 18S and 28S rRNA genes (White et al 1990). The PCR conditions were those described by Lehtonen et al (2008). The size and quality of PCR products were checked by electrophoresis of an aliquot (5 ll) of the reaction on a 1% agarose gel (w/v TAE electrophoresis buffer; ethidium bromide 0.1 lg/ml) and viewing the bands under UV-light.…”