Inocula of Gaeumannomyces graminis var. Tritici for field and glasshouse studies

Abstract The food reserves of whole oat-grain inoculum of Gaeumannomyces graminis var. tritici (Ggt) are unrealistically large compared to infective propagules in field situations, so in this study we examined the infectivity of different sized fractions of the ground oat inoculum. Minimum disease was obtained with the fraction Alternative forms of Ggt inoculum were developed and tested. Attapulgite amended with nutrient solution and seeds of ryegrass, millet and oats were colonized by Ggt and assessed in glasshouse experiments as forms of inoculum of the pathogen. Inocula in ryegrass and millet seed were also assessed in field trials. Attapulgite colonized by Ggt produced infection but had no effect on shoot growth of wheat seedlings in a glasshouse experiment. Both ryegrass and millet seed-borne propagules of Ggt reduced shoot weight of wheat seedlings in a glasshouse experiment. Increasing inoculum densities of ryegrass seed inoculum in glasshouse experiments and of ryegrass or millet seed inocula in field experiments produced dose responses in disease, plant growth and grain yield. Transmission electron microscopy of the different forms of inoculum showed that most of the hyphae of Ggt in attapulgite were moribund, whereas hyphae in the seed inocula were viable and contained many lipid droplets and melanin particles.