Development of infection structures by the direct-penetrating soybean rust fungus (Phakopsora pachyrhizi Syd.) on artificial membranes.
1988
Koch E. | Hoppe H.H.
The development of infection structure by the directly infecting soybean rust fungus of different artificial membranes was followed by light and scanning electron microscopy. On water agar uredospores developed germ tubes without appressoria. On dialysis membranes more than 80 per cent of the uredospores formed appressoria. With low frequencies (1-7 per cent) also primary hyphae and/or penetration hyphae were present. When cellulose nitrate membrane filters with pore diameters greater than or equal to 0.2 microm were used, uredospores germinated but showed a strongly reduced appressoria formation. Membranes with pores less than or equal to 0.1 microm allowed a development of infection structures similar to that on dialysis membranes. In experiments with paraffin oil incorporated into collodion membranes more than 90 per cent of the uredospores formed appressoria, about 50 per cent of the appressoria developed hyphae. Ungerminated spores and germ tubes always contained 2 nuclei. In fully developed appressoria 4 nuclei were present. Compared with stomata entering rust fungi appressoria formation by Phakopsora pachyrhizi occurred more frequently and seemed to be less dependent on specific stimuli. Moreover, in most cases only few of the appressoria formed penetration or primary hyphae. The induction of these structures seemed to be dependent on further unknown stimuli.
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