Root Dissection: a Method of studying the Distribution of Active Mycelia within Root Tissue

Abstract

THE presence of saprophytic micro-fungi in the decomposing cortex of roots of rye-grass1 has been studied by a simple modification of a technique, described by Harley and Waid2, which was developed to study the active mycelia of root surfaces. Roots at various stages of decomposition, characterized by the colour and condition of the cortex, were selected from rye-grass (Lolium perenne L.) growing under field conditions. The roots were washed by agitation in ten changes of 10 ml. of sterile water, and were then cut into 2-mm. fragments from which the outer cortex was dissected, leaving the central cylinder comprising the inner cortex and stele. Dissection was carried out in dishes of sterile water using sterile forceps and scalpel; with practice this could be done by eye. The 2-mm. fragments of outer and inner cortex and of intact roots were placed on three separate series of plates of Czapek-Dox agar and incubated for a period of three weeks at 25° C. The results, summarized in Table 1, demonstrate the differences which occurred between the composition of the mycelial populations of the root surfaces of intact roots and those of the outer and inner tissues of the cortex of dissected roots. Some of the sterile species of fungi isolated from the inner cortex were rarely isolated from intact roots, presumably because they could not compete in mixed culture with such surface-inhabiting species as Trichoderma viride or Mucor spp.