Studies on fungi in the root region

Summary Fungal isolations were made from roots ofPhaseolus vulgaris after washing in sterile water, at monthly intervals throughout the life of the plant, and from other roots after dissection and after surface sterilization at certain plant ages only. A table is provided showing the relative importance of the most common species isolated in each of four clearly distinct microhabitats — the root surface, the cortex, the outer stele and the inner stele.Fusarium oxysporum andCylindrocarpon radicicola were the most frequently isolated fungi from the roots.Fusarium oxysporum was most abundant on young roots and seemed to be associated, particularly, with the root surface and cortical tissues.Cylindrocarpon radicicola, although common on young roots, was more abundant on older roots and was an important initial colonist of the stelar tissues. Sterile mycelia were isolated mainly from older roots and seemed to be responsible, withC. radicicola, for the initial colonization of the stele. Microscopic examination of roots showed the cortical tissues to be increasingly penetrated by fungal hyphae with plant age but extensive fungal penetration of the endodermis and stelar tissues did not occur until the plants were at least five months old.