Etiology of rachis tip dieback of macadamia flowers in Australia.
Xu X, Rincon-Florez VA, Carvalhais LC, Akinsanmi OA.
Crop Improvement
Macadamia nuts in your grocery store could become harder to find and more expensive as this newly characterized disease complex quietly destroys the flowers before nuts can even form.
Macadamia trees have been suffering from a condition where the tips of their flower clusters die off, threatening nut production. Scientists studied sick flowers from 20 orchards across Australia and discovered that several types of fungi are the real culprits — not just weather or stress as previously thought. Some of these fungi, including two newly identified ones, had never before been known to attack macadamia flowers.
Key Findings
Three fungal species — Neopestalotiopsis maddoxii, N. macadamiae, and Epicoccum italicum — were confirmed as the primary causes of rachis tip dieback through infection experiments, with Neopestalotiopsis being the most commonly isolated genus (27.5% of samples).
20 different fungal genera were identified from 307 diseased flower samples across 20 commercial orchards in Australia during the 2023 and 2024 flowering seasons.
Two fungal groups, Diaporthe and Epicoccum, are reported for the first time as pathogens of macadamia flower clusters, expanding the known disease complex.
chevron_right Technical Summary
Researchers identified the fungal causes of a damaging macadamia flower disease called rachis tip dieback (RTD), finding that multiple fungal species — not environmental stress alone — are responsible for killing the flower stalks that macadamia nuts grow from.
Abstract Preview
Botrytis blight, Cladosporium blight, Pestalotiopsis blight and Phytophthora blight are distinct diseases of macadamia flowers. Rachis tip dieback (RTD) is part of the symptoms associated with all ...
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Macadamia is a genus of four species of trees in the flowering plant family Proteaceae. They are indigenous to Australia—specifically, northeastern New South Wales and central and southeastern Queensland. Two species of the genus are commercially important for their fruit, the macadamia nut. Glob...