Abstract
Mycosphaerella cryptica is one of the most destructive foliar pathogens of eucalypts in plantations in southern Australia. The majority of research on this pathogen has been conducted in plantations, with little focus on its distribution and impact on eucalypts in native forest. Tuart (Eucalyptus gomphocephala) is magnificent woodland tree endemic to Western Australia. With almost 75% of its original area cleared and concerns for the health of those remaining, the recruitment of tuart is highly important. The study of pathogens and pests that pose a threat to seedling survival will contribute to ensuring the regeneration of the remaining woodlands. Mycosphaerella cryptica has been recorded on E.marginata (Jarrah), E. diversicolor (Karri) and E. patens (Blackbutt) in native forests. In the present study we carried out surveys of regenerating stands of tuart between 2003 and 2005, confirming the presence of M. cryptica throughout all stands surveyed, and in some cases contributing to mortality of seedlings. These findings are somewhat surprising given M. cryptica has not previously been recorded from tuart in native forests.
In addition to these surveys, trials were established in Yalgorup N.P. in the native forest to investigate how the presence/absence of ashbeds and competition with midstorey (mainly Agonis flexuosa) affects the survival and growth of planted seedlings. These trials were assessed seasonally over a 14 month period for phytophagous insect attack and fungal pathogen damage. Initial assessments at 12 weeks confirmed the presence of M. cryptica associated with leaf lesions (also known as Crinkle Leaf). Over the subsequent 12 month period the severity of Crinkle Leaf increased across the trial and in some cases resulted in seedling mortality. In comparison to phytophagous insect damage, at the final assessment Crinkle Leaf was by for the most dominant category of damage.
Comparisons were made between the climatic conditions, seasonal growth patterns, and severity of Crinkle Leaf at the study site and in eastern Victoria where previous studies on M. cryptica have been conducted. Seasonal periods of infection by M. cryptica differed between the two sites. We propose that this is due to optimal conditions for spread and infection of the pathogen, and growth of the seedlings occurring in winter in Yalgorup N .P. compared with summer in eastern Victoria.
Knowledge gained in this study provides important information for disease management and will benefit restoration/regeneration initiatives of this threatened species of eucalypt.