Occurrence and possible role of endophytic fungi associated with seed pods of Colophospermum mopane (Fabaceae) in Botswana

Endophytic fungi were isolated from different aged surface sterilised pods of Colophospermum mopane and succession patterns were investigated. Lignocellulolytic enzyme assays as well as histological and fine structural studies were used to investigate if succession was related to different lignocellulolytic abilities of the fungi. Representatives of the common genera (Alternaria, Phoma and Phomopsis) were qualitatively tested for lignocellulolytic enzyme activity. Samples of endophyte infected and uninfected pod pericarps were fixed and sectioned for light microscopy and TEM. Samples were also viewed with SEM. A fungal succession was evident as pods aged, and detached from the tree. Strains of all three genera demonstrated lignocellulolytic abilities. Microscopy studies suggested that Phoma was only capable of utilising moderately lignified mesophyll cells whereas Phomopsis and Alternaria could degrade heavily lignified fibres. This could explain the pattern of succession observed: Phoma colonised younger pods where more unlignified resources were available, whereas Phomopsis and Alternaria colonised older pods, thus making use of the remaining lignified resources. Changes in endophyte abundance and diversity are related to the age and degree of decay of the pods, and determined by the lignocellulolytic abilities of the fungi. The potential role of these endophytes is discussed.