Abstract
Lengths (2 cm) of sterile wheat root were placed on margins of colonies of Gaeumannomyces graminis (Sacc.) Arx and Olivier var. tritici Walker (GGT) and Phialophora graminicola (Deacon) Walker (PG). Patterns of invasion by the fungi and host responses to infection were recorded for up to 8 days' incubation and were related to patterns of cortical cell death as determined by nuclear staining in uninoculated root pieces incubated on water agar (WA). Isolates of GGT that differed in virulence in a seedling assay penetrated root pieces at different rates but always faster than did PG. Prior incubation of root pieces on WA, until some of their cortical cells had senesced, enhanced the rate of penetration by PG, which seemed to depend on cortical senescence for invasion. Root pieces responded similarly to invasion by GGT and PG, by production of lignified papillae, general lignification of cortical cell walls and, in some instances, marked lignification of stelar ground tissues. None of these reactions occurred far in advance of penetrating hyphae. Root pieces with attached tips continued to grow on potato-dextrose agar (PDA) but less well on WA. Pieces with or without tips formed root laterals on PDA but not on WA. Cortical senescence also was delayed on PDA compared with on WA.
Published Version
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