The leaves looked ordinary at first, pale, tired green, edges curling slightly. The kind of damage that could be dismissed as stress or a passing infection. But beneath those blighted patches, something else was unfolding.
Deep within the infected Eucalyptus leaves, a fungus lived quietly, present, active, yet invisible to routine detection methods. It did not behave as expected. In the laboratory, it left no trace.
And so, it remained hidden. It was during investigations into Calonectria leaf blight (CLB) that PhD scholar Sabyasachi Banerjee and his team at the Forest Research Institute, Dehradun, realised something was amiss. Samples collected from infected leaves were brought into controlled lab settings and placed on standard media — where fungi are expected to grow, reproduce, and reveal themselves.
But this one refused. No spores formed. No structures appeared. Even under forced sporulation conditions, techniques routinely used by plant pathologists to coax fungi into revealing themselves, there was only silence.
It was, in every measurable way, absent. And yet, it was not.
Because when those same isolates were placed back onto living leaves, the story changed completely. The fungus came alive in its natural environment, spreading across healthy Eucalyptus clones, producing severe blight symptoms that could not be ignored. The pathogen was real, active, and aggressive.
It simply refused to exist under artificial conditions. Then came the moment of recognition. On the infected leaves, away from petri dishes and controlled environments, the fungus began to reveal its form. It produced its reproductive structures only there — on the host itself — as if the leaf was not just a surface, but a requirement.
Among these structures were something entirely unexpected: vesicles shaped like the caudal fin of a fish. Delicate, distinctive, and unlike anything previously documented within the fungal genus Calonectria.
It was a detail small enough to miss, but significant enough to change everything.
To understand what they were looking at, the researchers turned to genetics. Using multilocus phylogenetic analyses, they examined DNA sequences across multiple gene regions, mapping the organism’s place within the fungal world. The results were clear. The fungus formed a distinct, well-supported lineage — closely related to Calonectria tonkinensis, but separate, unique.
It was something new. It was named Calonectria caudovesiculata — a nod to its defining feature, the fish tail-like vesicles that had first set it apart. But the discovery was not just about naming a species. It was about what had almost been missed.
“The discovery highlights that relying only on culture-based laboratory methods can sometimes cause scientists to miss important plant pathogens. In this case, the fungus would likely have remained unidentified if researchers had not studied its structures directly on infected plant tissue and combined those observations with DNA-based analysis,” Sabyasachi Banerjee told TNIE.
The implications extend far beyond the laboratory. Calonectria leaf blight is not a minor inconvenience. In nurseries and young plantations, where warmth and humidity create ideal conditions, it spreads quickly. Leaves wither. Stems weaken. Entire plants can die. For a species like Eucalyptus widely cultivated for timber, paper, and oil the losses are not just biological, but economic.
Banerjee noted that severe infections can lead to defoliation, stem necrosis, and even plant mortality, affecting plantation productivity and livelihoods tied to it.