ULTRASTRUCTURAL STUDIES OF SECONDARY SPORE FORMATION AND DISCHARGE INTHE GENUS ENTOMOPHTHORA

Secondary spore formation and discharge among members of the genus Ent omophthora s.str. was studied at the ultrastructural level. The studie d members (E. schizophorae, E. muscae, E. planchoniana, and Entomophth ora sp.) proved to be very similar in all overall aspects. On host cut icle, primary spores formed secondary spores. The wall covering the se condary spores consisted of two layers, an electron-dense outer layer and a translucent inner layer. Around the apex these layers were diffu se and around the base the outer layer was missing. After discharge, t he outer wall layer split into several laminae which became involved i n the adhesion of the spore to the substrate. After landing on a subst rate, secondary spores quickly formed germ tubes. The wall organizatio n of secondary spores was thus similar to the wall arrangement of prim ary spores and should be termed ''bitunicate.'' It is concluded that b oth spore types have the same mechanism of discharge: ''rounding off.' ' The secondary spore should, however, be regarded as the infective un it. (C) 1995 Academic Press, Inc.