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Category: Communication

Description: Raceme blights also known as flower blights are used to describe diseases and disorders of macadamia inflorescence worldwide. Flower blights reduce fruit set and control measures are limited. Knowledge of the disease cycle and epidemiological parameters is required. Therefore, the potential sources of inoculum for the three forms of flower blights of macadamia in Australia were investigated. Relative abundance of the inoculum (Ri) in remnant racemes and yellow halo leaf spot in macadamia canopy was quantified and the pathogenicity of the fungal isolates obtained from the plant materials was assessed on developing flowers. Ri >90% was recorded for Neopestalotiopsis species from both the remnant racemes and leaf spot, which indicates the materials are a source of inoculum for dry flower disease. Whereas, Ri <40% was recorded for Botrytis species, the causal agent of grey mould, and Ri = 70% for Cladosporium species, the causal agent of green mould, only from remnant racemes. Conidial suspensions and direct incubation with the plant materials resulted in severe flower blights on developing macadamia flowers. Disease severity using inocula from remnant racemes was significantly (P > 0.001) higher than inocula from leaf spot. This information is critical for flower blights control in macadamia orchards.