Banana fungus renamed. Or not?

The causal agent of black leaf streak (also known as black Sigatoka) in bananas was a fungus called Mycosphaerella fijiensis. The species has recently been renamed to Pseudocercospora fijiensis. Those familiar with the pathogen will recognize the new name as the (old) name of its asexual form (Mycosphaerella fijiensis was the name of its sexual form). What changed is that the nomenclature system has finally caught up with biology and no longer allows the coexistence of separate names for the sexual and asexual forms[1].

[Spore-producing hyphea of Pseudocercospora fijiensis]

Like many of the fungi that cause disease in plants, the causal agent of black leaf streak is a pleomorphic fungus, meaning that it occurs in various distinct forms. In this case, the fungus has both a sexual state (teleomorph) and an asexual one (anamorph).

The practice of giving separate names to the different forms of pleomorphic fungi has been debated since the middle of the 19th century. In 2011, the Amsterdam Declaration on Fungal Nomenclature made the case for an orderly transition to a single-name nomenclature system. Soon after, the one fungus, one name principle was codified in the International Code of Nomenclature for algae, fungi, and plants (Melbourne code).

One consequence of the unravelling of the Mycosphaerella genus is that Pseudocercospora is now recognized as a genus in its own right. In addition to Pseudocercospora fijiensis, the genus also includes the other primary causal agents in the so-called Sigatoka disease complex. These species changed genus because they have Mycosphaerella-like teleomorphs. The Mycosphaerella genus is now restricted to species that have real Mycosphaerella teleomorphs and its name will be changed to Ramularia.

Nothing is ever easy in the world of fungi.

[1] Crous: Global food and fibre security threatened by current inefficiencies in fungal identification in Philosophical Transactions of the Royal Society of London - 2016