Species of Helminthosporium have been detected as parasites on the leaves of 45 grasses in south eastern Queensland. Some of these fungi had conidia with basal hila, others with protruding hila. The latter group, found on 15 species of grasses was given detailed study. Using conidia obtained from leaves of the host, H. turcicum, H. monoceras, H. halodes, H. rostratum and H. holmii were identified. Isolates obtained from the various grass hosts were used in experiments to determine the effect of concentration of sucrose and of temperature on the characters of the conidia. Cross inoculation studies with the isolates were made using the grass hosts from which the isolates originally were obtained.
Three types of protruding
hila have been designated. Isolates identified as H. turcicum are characterized by an inconspicuum type of protruding hilum, isolates Identified as H. monoceras by a plenum type and isolates identified as H. halodes, H. rostratum and H. holmii by a projectum type of protruding hilum. In tho various aepects of the work with isolates of Helminthosporium from Queensland, the hilum was the conidial character that showed the least variation. In a given isolate, whatever the culture medium, the temperature of growth or the host species onto which it was inoculated, the hilum remained the same.
Under various conditions of growth, fungi identified from the literature as H.
turcicum and H. monoceras have been found to be constant in shape of conidia end hilum type. Nothing was found in the course of this work to suggest that H. turcicum and H. monoceras are not good species.
On the other hand, fungi identified from the literature as H. halodes, H. rostratum and H. holmii, exhibited considerable variation in the characters of the conidia under different conditions of growth. Variation occurred in the length, width, septation, shape and colour of conidia. The greatest variation occurred in the length and shape of conidia. In many instances, the change In the characters of the conidia was so great under different conditions that any one isolate could be referred to two different species.
The above three species are also characterised by the presence of accentuated end septa. A number of the isolates did not develop accentuated end septa under some of the conditions of growth investigated. In the absence of this character the isolates could be identified as H. micropus, a species characterized by a projectum type hilum and with other conidial characters similar to those described for H. halodes. For this reason it appears that there must be considerable doubt whether H. micropus is a good species.
Cross inoculation studies with isolates of Helminthosporium from a number of Queensland grasses have shown that a single host species may be parasitized by isolates obtained from eleven other grasses. It has also been demonstrated that conidial characters of a given isolate can vary according to the
host on which the fungus developed. The changes in conidial characters may be so great that a given Isolate might be referred to two different species when obtained either from different hosts or from the same host obtained at different times of the year.
The present studies on isolates of Helminthosporium with the projectum type hilum have shown that the species H. halodes, H. rostratum and H. holmii are not reasily distinguishable. For a given collection of Helminthosporium, tentative identification as one of these species, based on the characters of conidia developed on the host in nature may be upset by the development by that fungus, in culture or on the leaves of a host grass, of characteristics by which it could be assigned to another species. This situation implies that there are no
real differences between the three species that have been described. The proposed nomenclature of the species is therefore as follows:
Helminthosporium halodes Drechaler
syn. H. rostratum Drechsler
H. holmii Luttrell