Characterization of Phialophora spp. isolates from a Montana take-all suppressive soil and their use in suppression of wheat take-all caused by Gaeumannomyces graminis var. tritici (Ggt)

Sterile fungi isolated from a Montana take-all suppressive soil were identified as Phialophora spp. and were characterized morphologically. These Phialophora spp. isolates were nonpathogenic on wheat or barley in glasshouse experiments. They, however, did not confer a substantial protection of wheat and barley seedlings against Gaeumannomyces graminis var. tritici (Ggt) in glasshouse tests.;Ribosomal DNA (rDNA) fragments from four Phialophora and two Gaeumannomyces isolates were amplified with Polymerase Chain Reaction (PCR) using universal primers, cloned, and sequenced. Sequence comparison to known sequences of Phialophora spp. and Gaeumannomyces spp. revealed that the Phialophora isolates included in this study were very closely related to Gaeumannomyces and less so to other Phialophora spp. Sequence alignment allowed the design of primers to be used in detecting Phialophora sp. I-52 in the soil and on cereal roots. Phialophora sp. I-52 was tentatively identified as P. graminicola based on morphological and molecular analyses.;In vitro tests of antagonism involving Phialophora spp. I-52, I-58, as well as a Bacillus sp. strain L that originated from the same soil as I-52 and I-58, resulted in significant inhibition of Ggt growth.;Phialophora sp. I-52 was combined with Phialophora sp. I-58 and tested for Ggt suppression in the field and with Bacillus sp. L under glasshouse conditions. Neither the combination of the two Phialophora spp. nor that of I-52 and Bacillus sp. L conferred any advantage in controlling take-all over I-52 alone. Phialophora sp. I-52 and Bacillus sp. L were shown to successfully colonize wheat roots and were frequently and readily isolated over a two-month period.;Phialophora sp. I-52, when introduced on canola seed, proved to be an efficient biological control agent against wheat take-all in its original suppressive soil as well as in a highly conducive soil. In field experiments, Phialophora sp. I-52 reduced take-all infection and increased shoot weight and grain yield.;The antagonistic ability of Phialophora spp. towards Ggt is most likely due to competition for infection sites on wheat roots, competition for nutrients, particularly iron through the production of siderophores, and/or the production of diffusible antibiotic metabolites. Some evidence pointed to a possible role of I-52 in promoting the growth of wheat plants...