Hyphal Anastomosis Reactions, rDNA-Internal Transcribed Spacer Sequences, and Virulence Levels Among Subsets of Rhizoctonia solani Anastomosis Group-2 (AG-2) and AG-BI

Abstract

Hyphal anastomosis reactions, rDNA-internal transcribed spacer (ITS) sequences, and virulence of isolates representing Rhizoctonia solani AG-BI and six subsets of anastomosis group (AG)-2 (-2-1, -2-2 IIIB, -2-2 IV, -2-2 LP, -2-3, and -2-4) were compared. AG-2-4 is a subset described for the first time in this report. Anastomosis reactions within AG-BI and the listed subsets of AG-2 were generally strong but, between subsets, ranged from strong to a very weak "bridging" -type reaction. Anastomosis reaction alone generally did not provide adequate evidence for placement of an isolate into a subset of AG-2. Anastomosis reactions between AG-BI and the original subsets of AG-2 (-2-1 and -2-2) are very strong; for this reason, we propose that it be included as a subset of AG-2 (designation AG-2 BI). Subsets -2-3 and -2-4 show very weak bridging-type anastomosis reactions with all other subsets of AG-2 and thus may be candidates for independent AG status. Grouping within AG-2 based on rDNA-ITS sequences was consistent with the abovementioned subsets. However, grouping based on virulence as measured herein does not conform to established grouping patterns within AG-2 and does not seem useful as a group-defining criterion. A broad range of damage was observed among members of the most virulent subsets (-2-1, -2-2 IIIB, -2-2 IV, and -2-4), whereas other subsets (-2 BI, -2-2 LP, and -2-3) were similar to one another in causing a minimal level of damage. Group-specific primer pairs for each of the seven subsets of AG-2 were designed based on the abovementioned rDNA-ITS sequences. Primer pairs proved dependable and subset specific in polymerase chain reaction amplifications of purified genomic DNA from 109 isolates of R. solani and two isolates of binucleate Rhizoctonia. These primers will provide a simple and useful method for subset-specific characterization within AG-2 if further critical evaluations confirm their specificity.

Virulence and molecular characterization of Costa Rican isolates of Rhizoctonia solani from common bean

“…The amplification was made using the primers WB-A, WB-B, AG 1-IA, AG 1-IB, AG 1-IC, AG 1-ID, AG 4, AG 2-2, AG 2-2 IIIB and AG 2-2IV (Carling et al 2002, Godoy-Lutz et al 2008. Amplifications were performed a PTC-100 thermocycler (MJ Research), with a temperature profile of 95°C for 5 min for denaturing, 58-62°C, for 45s for annealing of the primer and 72°C for 1 min for extension.…”

“…Isolates can exist as multinucleate homokaryons or heterokaryons and present diverse mating strategies (homothallic or heterothallic) (González et al, 2012). Phaseolus vulgaris isolates belong mainly to AG 1 (6 subgroups), AG 2 (4 subgroups) and AG 4 (Carling, 1996;Schneider et al, 1997;Carling et al, 1999;Carling et al, 2002;Godoy-Lutz et al, 2003;GodoyLutz et al, 2008;González et al, 2006). When evaluated on the same plant species, virulence between AGs varies from highly virulent to non-virulent.…”

Assessing genetic diversity in the web blight pathogen Thanatephorus cucumeris (anamorph = Rhizoctonia solani) subgroups AG-1-IE and AG-1-IF with molecular markers

“…A few isolates that did not amplify were tested with other primers suggested by Carling et al (2002) and Godoy-Lutz et al (2008). PCR amplifications were performed by adding 1.0 μl DNA (80-100 ng), 5 μl of 10× Taq DNA polymerase buffer (50 mM KCl, 10 mM Tris-HCl (pH 9.0 at 25°C), 1.5 mM MgCl 2 and 0.1% (v/v) Triton X-100 when diluted 1:10), 4 μl of 1.25 mM of each dNTP, 0.8 μl of each 20 μM primers (forward and reverse) (Invitrogen, Carlsbad, CA, USA) and 0.4 μl of Taq DNA polymerase (5 U/μl) (Promega, Madison, WI, USA) to a 50 μl reaction mixture prepared with sterile nuclease free water.…”

“…Web blight is mostly caused by five genetically different subgroups: AG-1-IA, AG-1-IB, AG-1-IE, AG-1-IF and AG-2-2WB (Godoy-Lutz et al 2008). To a lesser extent, other isolates of AG-4 and AG-2-2 IV have been associated with WB symptoms (Carling et al 2002;Gálvez et al 1989). Isolates of AG-1-IE and AG-1-IF are the most widespread and collectively more virulent than other subgroups causing WB in the LAC region and have overcome cultivars with partial resistance (Beaver et al 2008;Godoy-Lutz et al 1996, 2000.…”

Molecular identification and pathogenicity of Rhizoctonia spp. recovered from seed and soil samples of the main bean growing area of Argentina

“…Recently, 13 AGs have been reported (Liu et al, 1993;Carling, 1996;Tu et al, 1996;Carling et al, 2002;Sharon et al, 2008). Some of them were further divided into subgroups based on cultural characteristics, epidemiological differences as well as rDNA-ITS and RFLP sequence analyses (GodoyLutz et al, 2003(GodoyLutz et al, , 2008Özkoç, 2008, 2013;Spedaletti et al, 2016).…”