Biological Control Breakthrough

Embrapa, Unesp, and QueenNut Identify Native Bacteria to Control Macadamia Diseases

Serratia and Bacillus Strains Target Raceme Blight and Stem Rot in Expanding Brazilian Orchards

What is the core discovery regarding the macadamia crop protection research?
Joint research conducted by Unesp, QueenNut, and Embrapa Meio Ambiente has identified that two bacteria naturally associated with macadamia plants—Serratia ureilytica and Bacillus subtilis—show high efficiency in managing shoot and canopy diseases. These native microorganisms offer a sustainable biological tool against raceme blight and trunk rot, two major threats limiting the longevity and profitability of orchards in Brazil.

How does the control of shoot diseases impact macadamia cultivation?
According to researchers, the control of shoot diseases represents one of the main challenges for the sanitary management of macadamia. While conventional chemical methods face rising resistance and consumer pushback, leveraging indigenous bacteria ensures higher field survival rates, limits fungal sporulation, and preserves flower structures necessary for high fruit yield.

What are the next developmental milestones for this biological technology?
While greenhouse and nursery trials successfully validated that Bacillus velezensis and Bacillus subtilis reduce stem lesions across various scion-rootstock combinations, large-scale commercial adoption requires further engineering. The scientific team is currently focusing on developing stable bio-input formulations, evaluating compatibility with non-copper chemical controls, and confirming the economic viability of the solutions.

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Research led by São Paulo State University (Unesp), QueenNut, and Embrapa Meio Ambiente (SP) has identified that two bacteria naturally associated with macadamia—Serratia ureilytica and Bacillus subtilis—are highly promising for controlling shoot diseases. Pathogens affecting flowers and stems compromise productivity, orchard longevity, and crop profitability in a market that is rapidly expanding across Brazil. Studies are now advancing toward developing commercial bio-inputs based on these microorganisms.

The isolation of these native bacteria marks an important milestone in the biological control of two primary phytosanitary issues in Brazil: raceme blight (which destroys flower clusters) and stem rot/trunk rot. The findings are part of Marcos Abreu’s doctoral thesis at Unesp, advised by Embrapa Meio Ambiente researcher Bernardo Halfeld. The research built upon an epidemiological survey initiated in 2018 and published by Embrapa in 2024, which systematically mapped major pathogens in commercial macadamia regions.

“The control of shoot diseases represents one of the main challenges for the sanitary management of macadamia,” notes Bernardo Halfeld. “The results demonstrate that microorganisms naturally associated with the crop can significantly mitigate damage from critical diseases, contributing to a more profitable, resilient, and sustainable production system.”

Native Microorganisms Combating Raceme Blight

Raceme blight, caused by the fungus Cladosporium xanthochromaticum, attacks floral structures and severely limits fruit formation. Researchers screened 104 bacterial isolates extracted directly from macadamia flowers. Serratia ureilytica and Bacillus subtilis stood out for their ability to restrict both disease incidence and fungal sporulation.

Reducing spore production is an essential epidemiological strategy as it curbs the secondary spread of the pathogen through the orchard. The bacteria employ multiple simultaneous mechanisms, including the production of volatile and non-volatile antifungal compounds alongside direct nutrient competition. Because these strains are indigenous to the plant, they possess a pre-established physiological adaptation to survive real-world field conditions. In compatibility testing, the strains proved resilient alongside common agricultural inputs, showing sensitivity only to copper-based compounds.

Advancing Biocontrol Against Stem Rot

The second branch of the study targeted stem blight and trunk rot, induced by Lasiodiplodia pseudotheobromae. This aggressive disease causes woody tissue lesions, branch dieback, and tree mortality, particularly in young grafted plants. Greenhouse evaluations using Bacillus velezensis and Bacillus subtilis demonstrated significant reductions in lesion severity through the secretion of specialized antifungal metabolites.

The study clarified that the specific cultivar and rootstock combination heavily influences biocontrol efficacy. Certain genetic matches showed lower initial susceptibility and allowed the beneficial bacteria to operate more effectively, underscoring the need to pair biological inputs with proper agronomic material selection.

About the Published Research:

The scientific findings have been peer-reviewed and published in two distinct papers: “Efficacy of indigenous bacterial antagonists from the anthosphere of Macadamia integrifolia in controlling Cladosporium raceme blight” and “Biocontrol potential of stem blight in macadamia by Bacillus spp. in plantlets with different scion-rootstock combinations,” co-authored by researchers from Unesp, QueenNut Macadâmia, and Embrapa Meio Ambiente.

Embrapa Meio Ambiente & Unesp – Phytosanitary Research Update

Dois Córregos, SP, Brazil | May 2026 | embrapa.br/meio-ambiente