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

Abstract

pH is one of the major ambient factors affecting life history traits of soilborne phytopathogenic fungi. The diversity of phenotypic responses to pH changes has not been extensively explored within fungal populations. To investigate this question, 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 belonged to the G1 type and 45 to the G2 type, the two main genetic groups identified in Ggt populations. The experiments were conducted in Petri dishes on Fahraeus solid media buffered at pH 4Á6, 6Á0 or 7Á0 with citrate-disodium phosphate solutions. The 82 strains exhibited a wide range of hyphal growth rates at the three pH levels. Ten statistically different pH profiles were described. The G2 strains grew significantly better than the G1 on the slightly acidic (pH 6Á0) and the neutral (pH 7Á0) buffered media. The ability of three strains to change ambient pH was also measured on unbuffered Fahraeus solid media initially adjusted to pH 5Á6 or 8Á0. 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. These results provide the first evidence of intraspecific variability in pH sensitivity within soilborne fungal species.

pH effect on strain-specific transcriptomes of the take-all fungus

“…On the contrary, PG38 grew significantly better in a neutral medium than in an acidic environment. These growth rate profiles are representative of the interspecific variability of Ggt populations [8,11]. The growth profiles were different between strains according to the pH making relevant the study of the molecular basis regulating these two distinct phenotypes.…”

“…Within Ggt species, evidence of intraspecific variability in pH sensitivity was demonstrated: some strains grew better at neutral pH and other at acidic pH [11]. More precisely, G1 and G2 strains are known to respond differently to the pH factor: whereas G1 and G2 strains have similar growth rate profile on acidic medium, G2 strains present a significantly better growth rate on neutral medium [11].…”

“…Within Ggt species, evidence of intraspecific variability in pH sensitivity was demonstrated: some strains grew better at neutral pH and other at acidic pH [11]. More precisely, G1 and G2 strains are known to respond differently to the pH factor: whereas G1 and G2 strains have similar growth rate profile on acidic medium, G2 strains present a significantly better growth rate on neutral medium [11]. The mechanisms underlying the differential response of Ggt strains to the pH variations of the environment are not yet elucidated but extracellular pH has been shown to regulate Ggt gene expression involved in pathogenesis and saprophytic growth [8], in an original strain-specific way.…”

Fungal growth is affected by and affects pH and redox potential (Eh) of the growth medium

“…Comparing fungal growth on media with a range of pH has already been performed (Daval et al, 2013, Lebreton et al, 2014. However, when chemical compounds are added to the growth medium, it is difficult to disentangle the effects via pH from directs effects (Bekker et al, 2009).…”

“…At the field scale, opposite effect can be observed for wheat soilborne diseases: take-all (Gaeumannomyces graminis var. tritici) is more severe in alkaline soils (Smiley, 1974;Lebreton et al, 2014) and cephalosporium stripe (Cephalosporium gramineum) severity increase with soil acidity (Stiles & Murray, 1996). Soil pH is considered as a major structuring ambient factor of telluric microbial communities and plant microbiome (Rousk et al, 2010;Chapelle et al, 2016).…”