Structure and lysis of microsclerotia of Verticillium dahliae in soil

Microsclerotia of Verticillium dahliae placed in soils of high and low pH quickly became colonized by bacteria. Fungal colonization was also observed in both soil types. Bacterial colonization was more prevalent in soil of high pH while fungal colonization was most evident in soil of low pH. Various bacteria seemed to be involved in the colonization of the microsclerotia. Some were attached to the microsclerotial cell walls and seemed to cause a swelling of the walls; others appeared to be embedded in the remains of cell walls which had lost their electron-dense structure and appeared to be lysed. Bacteria were also found to penetrate microsclerotial cells through pores in the cell walls. Fungal penetration of microsclerotial cell walls was observed less frequently, but fungal structures were observed in and around microsclerotial cells. Microsclerotia incubated in soil for 3 months showed considerable loss of electron-dense material situated within the matrix between the cells which appeared to indicate deterioration of pigmented material.