In Trieste, researchers just unveiled how one of agriculture's most destructive fungi pulls off an astonishing feat of invasion: it shrinks itself to microscopic proportions and slips into the tiniest spaces inside tomato roots. Fusarium oxysporum, a soil-borne pathogen that has devastated tomato crops worldwide, has long been known as a vicious killer—it clogs the vascular system and starves plants of water, causing wilt that can wipe out entire harvests. But how exactly this fungus sneaks inside and spreads through plant tissue at such a fine scale has remained largely invisible to science, until now.
Researchers at Elettra Sincrotrone Trieste used an extraordinary imaging technique called synchrotron radiation phase-contrast X-ray microtomography (SR PC-microCT) to watch the infection unfold in three dimensions, with resolution fine enough to see nanoscale spaces. The experiments, conducted at the SYRMEP beamline, revealed something remarkable: Fusarium oxysporum doesn't just push its way into roots—it fundamentally transforms its own body to slip through them. The fungus can reduce its hyphal diameter by more than twenty-fold, allowing it to colonize spaces so small they're barely visible even under conventional microscopes. Once inside, it spreads through the xylem and apoplastic compartments, progressively disrupting the root's architecture from within.
What makes this discovery particularly significant is the imaging method itself. Unlike traditional optical microscopy, which requires slicing samples into fragments and loses the full three-dimensional context, synchrotron-based phase-contrast imaging allows researchers to peer inside intact roots without destroying them. The technique preserves the native organization of tissues while simultaneously showing fungal distribution, the formation of air-filled blockages called embolisms that form along the root axis, and the progressive damage to the plant's internal structures. The images reveal dense structures of fungal biomass colonizing the vascular system, alongside elongated embolisms aligned with the root axis—the very mechanism that chokes off water transport and kills the plant.
The research, led by Valentino Maria Guastaferro and colleagues and published in Nature Communications, combined the synchrotron imaging with fluorescence microscopy and advanced image analysis to paint the fullest picture yet of how a vascular pathogen conquers a plant from the inside. This matters because understanding precisely how pathogens invade and spread—down to their mechanical strategies and structural transformations—opens the door to new defensive approaches. Rather than guessing at what happens inside intact roots, scientists can now watch it happen, step by step.
As soil-borne fungal pathogens continue to cause major agricultural losses worldwide, this window into their colonization strategies represents a crucial shift. The findings demonstrate that synchrotron-based phase-contrast microtomography could become a powerful tool for studying plant-pathogen interactions in other crops and fungal species. The more we can see, the better we can fight back.