Among the five major citrus diseases threatening Europe, our primary focus is on:

• Huanglongbing (HLB) or Citrus Greening – Caused by the gram-negative bacteria Candidatus Liberibacter spp. and transmitted by carrying insects(Diaphorina citri and Trioza erytreae) that feed on citrus trees. HLB weakens the plant’s immune system, allowing the infection to spread silently. Therefore, infected trees don’t look sick right away and it can take months before symptoms appear. During this time, the disease can spread silently through an entire orchard, making early detection and control absolutely critical..
• Citrus Black Spot (CBS) – Caused by the fungus Phyllosticta citricarpa, this disease primarily affects the peels and leaves of citrus plants. Unlike HLB, it does not require an insect carrier and spreads via wind from tree to tree. The fungus remains dormant under the fruit’s skin for several months before symptoms become visible.

This is how the fruits of the orange trees look like when they are infected by HLB or CBS.

At Citrusbusters, we collaborate with 11 partners, mainly from Europe, and one important partner in Brazil.. Our contributions focus on microbial community analysis. We study the microorganisms of different parts of citrus plants and its surrounding such as the soil around the roots (rhizosphere), the surface of the leaves (phyllosphere) and the soil. We take samples from both healthy and diseased plants, and plants that may be infected but are not yet showing symptoms.This helps us understand how these microbial communities change when citrus trees are affected by HLB or Citrus Black Spot.

1. Biocontrol strategies – Just like the human gut microbiome helps us stay healthy, citrus trees also rely on their own community of helpful microbes. By studying the microbiome of healthy citrus plants, we aim to identify beneficial microbes that could be used to combat infections. We are exploring the potential of microbial “cocktails” (consortia) and even moving soil from healthy trees to diseased ones, to help citrus trees build natural resistance against HLB and Citrus Black Spot.
2. Early detection and predictive models – We combine microbiome data with partner research on plant signals (such as smells, chemical changes, imaging, and sensor data). Using this information, we build predictive models to spot early microbial “warning signs” of disease. This makes it possible to detect problems before symptoms appear and supports better decisions for protecting citrus trees.