Fungal penetration of the cyst wall of Heterodera glycines

Twelve fungal species were examined with the aid of light, scanning electron, and transmission electron microscopy to determine their capability to penetrate the cyst wall of Heterodera glycines. Arthrobotrys dactyloides, Dictyochaeta heteroderae, Exophiala pisciphila, Fusarium oxysporum, Neocosmospora vasinfecta, Paecilomyces lilacinus, Pyrenochaeta terrestris, Stagonospora heteroderae, Verticillium chlamydosporium, and a sterile fungus (black, yeastlike fungus) were observed to penetrate the cyst wall of Heterodera glycines. The light microscopy procedure reported herein was useful for determining the direction of fungal penetration of the cyst wall. Also, the procedure allowed for the examination of many specimens. Nine of these fungi penetrated the cyst wall from inside the cyst. At least three species, Exophiala pisciphila, Fusarium oxysporum, and Pyrenochaeta terrestris, also penetrated the cyst wall from the outside. Penetration by the black, yeastlike fungus was limited to the outer layers of the cyst wall. No fungal penetration was observed on cysts exposed to Gliocladium catenulatum or Hirsutella rhossiliensis for up to 1 month.