Ultrastructural Studies of Secondary Spore Formation and Discharge in the Genus Entomophthora

Abstract

Secondary spore formation and discharge among members of the genus Entomophthora s.str. was studied at the ultrastructural level. The studied members ( E. schizophorae, E. muscae, E. planchoniana, and Entomophthora sp. ) proved to be very similar in all overall aspects. On host cuticle, primary spores formed secondary spores. The wall covering the secondary spores consisted of two layers, an electron-dense outer layer and a translucent inner layer. Around the apex these layers were diffuse and around the base the outer layer was missing. After discharge, the outer wall layer split into several laminae which became involved in the adhesion of the spore to the substrate. After landing on a substrate, secondary spores quickly formed germ tubes. The wall organization of secondary spores was thus similar to the wall arrangement of primary spores and should be termed "bitunicate." It is concluded that both spore types have the same mechanism of discharge: "rounding off." The secondary spore should, however, be regarded as the infective unit.