Relationship of microscopic and macroscopic vegetative reactions in Rhizoctonia solani and the occurrence of vegetatively compatible populations (VCPs) in AG-8

An examination of microscopic and macroscopic vegetative reactions between paired isolated of Rhizoctonia solani AG-8 revealed that pairs of isolates that give a C2 anastomosis reaction at the microscopic level always gives a ‘tuft’ reaction at the macroscopic level. Similarly, any pair that gives a C3 anastomosis reaction at the microscopic level always gives a ‘merge’ reaction at the macroscopic level. Thus, macroscopic vegetative (‘tuft type’) reactions can be used to predict the microscopic (anastomosis) reaction (and vice versa) between paired isolate of AG-8. This pattern also seems to apply to paired isolates of AG-3, AG-7 and AG-10 but not the other AGs of R. solani . The C2 anastomosis reaction is always observed when two isolates from different zymogram groups of R. solani AG-8 are paired. When isolates from within any of the five zymogram groups comprising AG-8 are paired, either a C2 or a C3 anastomosis reaction will result. Many field isolates of AG-8, when paired, give a C3 anastomosis reaction. We propose that a group of field isolates of R. solani that give a C3 anastomosis reaction be designated a ‘vegetatively compatible population’ (VCP).