Studies on the perfect stage of Helminthosporium sativum

Cochliobolus sativus, the perfect stage of Helminthosporium sativum, developed in some paired cultures of monoconidial isolates. A satisfactory medium for the propagation of perithecia consists of kernels of barley placed on Sach's nutrient agar. The barley was prepared by surface sterilization, followed by boiling to kill the embryos. Cultural studies of monoascosporic isolates showed that the fungus is heterothallic in the sense that the isolates are hermaphroditic, self-sterile, intragroup sterile, and intergroup fertile. The change from a conidial to a mycelial-type colony in one isolate was shown to be a true mutation. The two compatibility groups in C. sativus were shown to be randomly distributed in nature. Isolates of the fungus from any one area were observed to fall into either compatibility group. A comparison of the author's C. sativus with the description of Ophiobolus sativus given by Ito and Kuribayashi led to the conclusion that these fungi are identical.