SUMMARY Techniques are described for the isolation of fungi inhabiting ericaceous roots and for the culture of mycorrhizas under aseptic conditions. The mycorrhizal status of a range of isolates is assessed and the distinctive features of the true endophyte are described. The biology of this fungus is considered with special reference to host specificity and its occurrence as a free living soil micro‐organism.

No abstract

SUMMARYIsometric virus‐like particles (VLP) measuring 35 nm and 27 nm occurred in cultured mycelium of Gaeumannomyces graminis var. tritici and G. graminis var. avenae. These VLP had, respectively, sedimentation coefficients (s°20, W) 148S and 110S and ultraviolet absorption (maximum 260 nm, minimum 240 nm) typical of nucleoprotein (A260:280 = 1.6, A260:240 = 1.2). Preparations of the 35 nm particles had two major and one minor component in caesium chloride, and 27 nm particles had two components (buoyant densities 1.37, 1.36, 1.30, 1.35, and 1.29 g/cm3 respectively). Preparations of the 35 nm particles or 35 nm plus 27 nm particles had one major protein species with estimated molecular weight 70000 daltons.The 35 nm VLP were absent from 11 isolates of G. graminis var. tritici from first cereal crops after fallow or non‐susceptible break crops; two of these contained the 27 nm particles. More than half of 145 isolates, from cereals after 2–12 consecutive susceptible crops, contained either 35 nm or 27 nm VLP. VLP were not confined to G. graminis isolates from soils exhibiting ‘take‐all decline’ nor consistently associated with weak pathogenicity or with isolates of unusual growth, morphology, pigmentation, lysis or readiness to form perithecia. Isolates with one kind of particle were mostly more pathogenic and those with both kinds less pathogenic than isolates without VLP. The proportion of isolates with 27 nm and 35 nm particles increased progressively in samples from different consecutive crops during the first 9 years of cropping, then decreased.Isolates did not gain or lose VLP during infection and re‐isolation from wheat seedlings grown in sand.Four ‘infected’ isolates were freed from VLP either by culturing ascospores or by growing hyphal tips excised from colonies kept near their thermal death point. Both VLP appeared in cultures which had undergone anastomosis with infected isolates.

SUMMARY Translocation of nutrients is demonstrated in mycorrhiza of ericaceous plants. [14C]glucose and [32P]orthophosphate are translocated over limited distacnes by the endophyte in pure culture. 32P is translocated to mycorrhizal host plants over distances and at rates which are related to the size of the host plants. Photosynthates from the higher plant are translocated from the roots to the external mycelium of the endophyte. The possible ecological significance of these findings is discussed.