Effect of metabolites of Aspergillus niger and Trichoderma viride on development and structure of radicle of cocoa (Theobroma cacao) seedlings

Both the volume and concentration of filtrate of Aspergillus niger and Trichoderma viride influenced the development of the radicles of cocoa seedlings. Radicles placed in Petri dishes containing filter paper moistened with 20 and 30 ml of undiluted filtrate and filtrate dilutions of 1:1 and 1:2 failed to develop lateral roots and eventually died. The culture filtrate of A. niger was more repressive. Radicles in the same volume of filtrate (20 and 30ml) of higher dilutions (1:5 and 1:10) developed lateral roots and survived. Radicles placed in less volume (≤ 10 ml) survived and produced lateral roots irrespective of concentration of filtrates. Development of the radicles and roots in the control was consistently better (P = 0.05) than in filtrate solutions of either A. niger or T. viride. The hypocotyls of seedlings under the influence of metabolites of A niger showed greater cambial activity and formed xylem vessels and tracheids with larger lumina.