Morphological analyses and molecular phylogenetics of Helminthosporium group of fungi

Thirty-nine isolates of Drechslera, Helminthosporium, Bipolaris and Exserohilum were differentiated on the basis of their morphology. All isolates showed either unipolar or bipolar germination with the germ tube emerging adjacent to the hilum and growing in the direction of the long-axis of the conidium (semi axial). However, there was considerable diversity in the shape (oblong, elliptical, oval, fusoid and navicular) and structure of conidia. The isolates germinating both at polar and bipolar ends having oblong, ellipsoidal and navicular conidia were considered as genus Bipolaris. The isolates having conidia with strong protuberant hilum and pale end cells cut off by thick septa and mostly ellipsoidal in shape were reported as Exserohilum. None of these characters were found in Drechslera group. Variations in morphological characters were complemented by internal transcribed spacer sequences. The sequences of isolates were highly homologous to those of Bipolaris and Exserohilum. Therefore, these fungi belong to the genus Bipolaris and Exserohilum.