Sensitivity to pH and ability to modify ambient pH of the take-all fungus Gaeumannomyces graminis var. tritici

pH is one of the major ambient factors affecting life history traits of soilborne phytopathogenic fungi. The diversity ofphenotypic responses to pH changes has not been extensively explored within fungal populations. To investigate thisquestion, the ability of 82 strains of a worldwide collection of the take-all agent Gaeumannomyces graminis var. tritici(Ggt) to grow in controlled pH conditions, reflecting their pH sensitivity, was measured. Of these 82 strains, 37 belongedto the G1 type and 45 to the G2 type, the two main genetic groups identified in Ggt populations. The experiments wereconducted in Petri dishes on Fahraeus solid media buffered at pH 4 6, 6 0or7 0 with citrate–disodium phosphate solu-tions. The 82 strains exhibited a wide range of hyphal growth rates at the three pH levels. Ten statistically different pHprofiles were described. The G2 strains grew significantly better than the G1 on the slightly acidic (pH 6 0) and the neu-tral (pH 7 0) buffered media. The ability of three strains to change ambient pH was also measured on unbuffered Fahrae-us solid media initially adjusted to pH 5 6or8 0. All three strains were able to alkalinize the acidic medium. However,important variations between strains in the intensity, range and persistence of this alkalinization were measured. Theseresults provide the first evidence of intraspecific variability in pH sensitivity within soilborne fungal species.Keywords: alkalinization, mycelium growth rate, pH, population, root disease, soil