Abstract
Extensive leaf spot was observed on all leaves of young macadamia trees planted in new orchards in Queensland, Australia. The loss in photosynthetic ability of these trees may contribute to their demise and poor establishment compared to trees without symptoms. A survey of fungal leaf spots on macadamia trees in 20 commercial orchards in Queensland revealed two distinctive types of symptoms. Leaves showing circular dark brown spots with yellow halos (Type 1) and irregular dark brown spots (Type 2) were collected. Fungal isolates associated with the infected leaves were identified by morphological characteristics and DNA sequencing as Neopestalotiopsis clavispora for Type 1 spots and Colletotrichum siamense for Type 2 spots. Koch’s postulates were fulfilled for N. clavispora and C. siamense. Pathogenicity assays showed that both fungi caused severe leaf spots, which are identical to the respective field disease symptoms. In order to clearly characterise them, the two leaf spots were named as Pestalotiopsis leaf spot (Type 1 spots) and Colletotrichum leaf spot (Type 2 spots). This is the first report of N. clavispora and C. siamense causing leaf spots in macadamia in Australia.
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