Subgeneric Division of Japanese Graminicolous Helminthosporia in Relation to Systematics of Host Plant

Abstract

A taxonomic consideration of some species was carried out to divide into subgenera Euhelminthosporium and Cylindro-Helminthosporium. Conidia of Helminthosporium brizae and H. dematioideum were observed to germinate by the production of lateral germ tubes from the basal cell. The mode of germination of conidia was employed as a key character in separating the two subgenera in Helminthosporium, agreeing to Luttrell's view, and both of the species were preferably placed in the subgenus Cylindro-Helminthosporium. In addition, H. zonatum also was included in Cylindro-Helminthosporium as based on a photograph attached to the original description by Ikata and Yoshida.From a review of the literature and the writer's observations on Helminthosporia parasitic on Gramineae in Japan, 19 species are enumerated as members of subgenus Euhelminthosporium, and 16 species for Cylindro-Helminthosporium. Only H. arundinis described by Nisikado and by Sawada is excluded because it needs further study to permit a satisfactory disposition.The host plants of respective subgenera of Helminthosporium clearly fall into two different groups of gramineaceous subfamilies sensu Stebbins and Crampton: i. e., Euhelminthosporium spp. are found to be parasitic on the grasses belonging to either subfamily Oryzoideae, Eragrostoideae or Panicoideae, while only one species, H. sorokinianum Sacc. ex Sorok., occurs on members of Festucoideae. On the other hand, all of the 16 Cylindro-Helminthosporium species occur on grasses of subfamily Festucoideae. It may be inferred that the grasses which are north temperate in distribution as represented by Festucoideae are infected primarily by the species of Cylindro-Helminthosporium, whereas grasses with centers of distribution in the tropics and subtropics, such as Oryzoideae and Panicoideae, are infected primarily by the members of Euhelminthosporium.This relation apparently holds good in the other foreign species of Helminthosporium, though some exceptions have to be admitted. One of the exceptions is that H. giganteum Heald et Wolf occurs on tropical grasses though it belongs to subgenus Cylindro-Helminthosporium. It is interesting to note that H. giganteum has a very wide host range, as does H. sorokinianum, an exceptional species in Euhelminthosporium.