S.L. Jackson

PCR-identification of Mycosphaerella species associated with leaf diseases of Eucalyptus

A PCR-based technique based on the ITS1-5.8s-ITS2 domain of the rRNA gene for identifying five species associated with Mycosphaerella leaf disease (MLD) of eucalypts was developed. Primer pairs MC2F and MC2R; ML1F and ML1R; MM1F and MM1R; MN1F and MN1R; and MP1F and MP1R amplified a product for DNA extracted from their single target species, those being M. cryptica, M. lateralis, M. marksii, M. nubilosa and M. parva, respectively. The possibility of false positive amplification by each primer pair was tested in reactions with DNA extracts from 16 other Mycosphaerella species associated with eucalypts and against non-infected Eucalyptus globulus leaves. Under the PCR conditions used, there were no false positive amplifications of the 16 non-target Mycosphaerella species, or from non-symptomatic E. globulus leaves for the primer pairs ML1F and ML1R; MM1F and MM1R; MN1F and MN1R; and MP1F and MP1R. The primer pair MC2F and MC2R amplified a 402 nt product from both the target M. crvptica and non-target M. nubilosa. However, these two species were differentiated by digesting the product with the restriction enzyme Sacc II which resulted in a single 402 nt product for M. cryptica, and two products of 78 and 324 nt for M. nubilosa. All of the primers were able to detect their target Mycosphaerella species from Eucalyptus globulus lesions. PCR reactions with these primers on DNA extracted from Mycosphaerella lesions confirmed the presence of all five species from leaf material collected from three plantations in Western Australia.

Infection, hyperparasitism and conidiogenesis of Mycosphaerella lateralis on Eucalyptus globulus in Western Australia

Mycosphaerella lateralis has been isolated from diseased eucalypt foliage in conjunction with the known pathogens M. cryptica and M. nubilosa. This study sought to determine whether Dissoconium dekkeri, the anamorph state of M. lateralis, infects healthy eucalypt leaves or is a hyperparasite of M. cryptica or M. nubilosa. Detached Eucalyptus globulus leaves were inoculated with conidial suspensions of M. lateralis and the progress of leaf infection studied over 6 days. Clearing and staining of the leaves showed that infection occurred via stomata after 3 days. In order to determine whether M. lateralis is a hyperparasite of M. cryptica or M. nubilosa, colonies of these species were grown adjacent to one another on either water agar, 0.2% malt-extract agar (MEA) or 2% MEA. No evidence of M. lateralis parasitising M. cryptica or M. nubilosa was found. This indicates that M. lateralis may be a foliar pathogen, rather than a hyperparasite as was previously suggested. Scanning electron microscopy was used to show that conidiogenesis of M. lateralis is both percurrent and sympodial.

New records of Mycosphaerella leaf disease from Eucalypts in Western Australia

Eight new host records of Mycosphaerella leaf disease (MLD) are described from plantation and endemic eucalypts in Western Australia, extending the host range of Mycosphaerella nubilosa, M. marksii and M. parva.

New records of Mycosphaerella species from Eucalypts in Queensland

Recent surveys of the Eucalyptus plantation estate in Queensland for Mycosphaerella leaf disease found five new host records and three new records for Queensland.