160 million years ago, this fungus pierced trees like a microscopic spear

Molecular phylogenetic analyses suggest that blue-stain fungi should be an old fungal group, which might originate during the Late Paleozoic or early Mesozoic. However, hardly anything is known about the geological occurrences of blue-stain fungi. "Not until 2022, the first credible fossil record of blue-stain fungi was reported from the Cretaceous in South Africa with an age of approximately 80 million years," says Dr. Ning Tian from Shenyang Normal University in Shenyang, China.

A Chinese research team led by Dr. Ning Tian and Dr. Yongdong Wang (Nanjing Institute of Geology and Palaenology, CAS) found well-preserved fossil fungal hyphae preserved within a Jurassic petrified wood from northeastern China, dated 160 million years ago. Microscopic examination reveals the fossil hyphae are dark in color, which is indicative of pigmentation, a hallmark of contemporary blue-stain fungi which results in the discoloration of woods. Of interest, when penetrating the wood cell wall, the hyphae commonly form a very specialized structure called "penetration peg" (Fig. 1). That is to say when pushing through the wood's cell walls, the hyphae commonly slim down in size, making it easier to pierce through the tough barrier. The discovery of the penetration peg enables the team to ensure that the fossil fungus that they found belongs to the blue-stain fungi. "Unlike wood-decay fungi, which degrade wood cell walls through enzymatic secretion, the blue-stain fungi lack the enzymatic capacity to decompose wood structures. Instead, their hyphae mechanically breach wood cell walls via the penetration pegs. " Dr. Tian says.

"The finding of Jurassic blue-stain fungi from China, represents the second report of the blue-stain fangi and the earliest fossil record of this fungal group in the world, pushes back the earliest known fossil record of this fungal group by approximately 80 million years, providing crucial fossil evidence for further understanding the origin and early evolution of blue-stain fungi. Additionally, it offers fresh insights into understanding the ecological relationships between the blue-stain fungi, plants, and insects during the Jurassic period," says Dr. Wang. The bark beetle subfamily Scolytinae is considered as one of the major spore dispersal agents for extant blue-stain. However, both molecular biological and fossil evidence proposed that the origin time of Scolytinae dates back no earlier than the Early Cretaceous. Given the Jurassic age of present fossil fungus, it is hypothesized that its spore dispersal vector was not Scolytinae but rather other wood-colonizing insects prevalent during that period.