Perforation of hyphae and sclerotia of Rhizoctonia solani Kuehn by mycophagous soil amoebae from vegetable field soils in Japan.

Abstract

Annular depressions and perforations in fungal cell walls were observed on hyphae and sclerotia of Rhizoctonia solani and on conidia of Cochliobolus miyabeanus following burial of these respective fungus propagules for 4 to 8 weeks in vegetable field soils obtained from various locations in Shikoku, Japan. The annular depressions and perforations were 1.0 to 5.5μm in diameter with 1 to 7 perforations per hyphal cell or conidium. Vampyrellid amoebae were isolated from soils and were estimated to number 2.0 to 33.0 per gram of soil. Trophozoites of the amoebae extended 500μm and more with extremely fine filopodia. Plasmotomy was common in large trophozoites before encystment. Digestive cysts were pale yellow, orbicular or elliptic and averaged 33.5×40.1μm in diameter. During excystment, trophozoites emerged through 10 to 20 holes 2.0 to 10.0μm in diameter in the cyst walls. Trophozoites engulfed hyphae in 5 to 20min after attaching to the fungal cell and emptied the contents of the cell within 40 to 90min for hyphae of R. solani and 60 to 120min for conidia of C. miyabeanus. Morphology of the trophozoites and cysts, the mode of encystment and excystment, and the feeding behaviour of the amoebae all match the descriptions for Arachnula impatiens Cienkowski.