First report of apple leaf blotch caused by Alternaria arborescens complex in New Zealand

Apple leaf blotch has been observed in Nelson and Hawke’s Bay regions of New Zealand over recent years. Fungi from the genus Alternaria were consistently obtained from symptomatic leaf material, and morphological and molecular analysis determined that these isolates belong to the Alternaria arborescens complex. Pathogenicity tests were carried out to determine if these fungi were the causal agents of the observed symptoms. Testing was conducted using both orchard and glasshouse grown apple leaves, but symptoms only occurred on young glasshouse grown leaves and only on some of the inoculated leaves. These results confirm that the A. arborescens complex is causing leaf blotch on apple leaves in New Zealand, but also suggest that the fungus is not an aggressive pathogen and disease development is likely dependent on additional factors like leaf age and physiology, climate or growing conditions.