Degradation of Uredospores of the Soybean Rust Fungus (Phakopsora pachyrhizi Syd.) by Cell‐Free Culture Filtrates of the Mycoparasite Verticillium Psalliotae Treschow

Verticillium psalliotae isolates Taiw and Thai C are effective parasites of the soybean rust fungus. Cell‐free culture filtrates of these fungi, prepared after growth on autoclaved uredospores, contained β‐1,3‐glucanase, chitinase and protease activities and caused degradations, when rust spores were treated with them for 24 or 72 h. During these lytic processes carbohydrates, amino compounds and N ‐acetylhexosamine were released. The carbohydrate fraction was composed of mannitol, arabitol, trehalose, glucose and unidentified substances showing low R f ‐values during thin layer chromatography. The amino compounds consisted of 10 amino acids (leucine and/or isoleucine, phenylalanine, glutamic acid, valine, arginine, asparagine, glutamine, serine, aspartic acid, histidine) and 5—7 substances which could not be identified. Verticillium lecanii isolate Konz is a weak parasite of soybean rust. During growth on uredospores the fungus produced culture filtrates without chitinase activity and with low total activities of β‐1,3‐glucanase and protease. Compared with V. psalliotae , culture filtrates of V. lecanii exerted lower lytic activities on soybean rust uredospores. The results are consistent with the aspect that the rapid growth of V. psalliotae on soybean rust fungus is primarily based on the secretion of lytic enzymes which make nutrients available to the mycoparasite.