Acharya Balkrishna and team identify new fungal family in global study

In a major milestone in mycology, a team of scientists led by Acharya Balkrishna has presented a thorough review of the rust genus Skierka, leading to its official classification under a new family, Skierkaceae.

This comprehensive review, published in the Journal of Fungi, presents new knowledge on the taxonomy, distribution, and ecological functions of Skierka, a genus that has hitherto defied definitive classification.

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The genus Skierka was originally described in 1900 by the Polish mycologist Mieczysław Raciborski, when it was named with the type species Skierka canarii. Throughout the subsequent decades, the genus has been affected by numerous taxonomic revisions.

In early classifications, Skierka was placed in the family Pucciniaceae, due to its morphological features.

These have, however, been followed by other studies indicating alignments with other families, such as Melampsoraceae and Pileolariaceae, based on shared characteristics like sessile and adhering teliospores.

Despite this, a general agreement on the genus’ accurate taxonomic position continued to elude scientists. This is because of its distinctive morphological characteristics that in the earlier studies did not fit well within recognised families.

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This has made it difficult to gain a full understanding of its evolutionary connections, as well as its ecological functions.

The new research by Balkrishna et al uses multidisciplinary approach. This approach goes on to combine morphological analysis with molecular phylogenetic methods. And, it further helps to clarify the taxonomic uncertainties in Skierka.

The scientists used extensive studies of spore morphology, host specificity, and ecological relationships, combined with molecular sequencing of ribosomal DNA regions like ITS, LSU, and SSU.

Phylogenetic studies showed that Skierka constitutes a monophyletic clade in the order Pucciniales. This is distinct from other genera of rust fungi. This result led in the creation of the new family Skierkaceae and suborder Skierkineae. This happens after relegating Skierka to an independent evolutionary lineage among the rust fungi.

Skierka species have a broad geographical range, with records from Asia, Africa, the Americas, and Oceania. The genus shows a significant host specificity in that they infect mainly members of the families Sapindaceae, Burseraceae, and Euphorbiaceae.

Interestingly, hosts like Skierka canarii and Skierka diploglottidis have been found on Canarium and Diploglottis species, respectively.

The study emphasizes the ecological importance of Skierka as a sole host-dependent biotroph, completing its life cycle on one host plant. This host-specific dependence of Skierka indicates the complex co-evolutionary interactions of Skierka and its host plants, providing important information on the mechanisms of plant-pathogen interaction.

The morphological characteristics of the Skierka species are crucial to their identification and classification. The researchers carefully recorded the spore morphology, indicating the occurrence of subepidermal, densified uredinia and fusoid teliospores with sharp apices.

They are uniform across the species. This serves as a valid basis for distinguishing between species within the genus.

Further, the research highlights the morphological variation in spores within various species, which, as a combination with host plant connections, allows for proper identification and differentiation of Skierka species.

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The recognition of Skierkaceae as a separate family of Pucciniales has a very significant implications for rust fungi evolution. The distinct morphological and molecular features of Skierka indicate an evolutionary divergence pathway. This possibly provides clues to the adaptive tactics used by rust fungi. The mechanism helps them cope with environmental stresses and host plant defense.

In addition, the findings of this particular study add to the larger body of work in fungal diversity. This happens by pointing to the need to combine molecular analysis and classical morphological investigations. As a result, it provides an in-depth understanding of the taxonomy and ecology of fungi.

With this research, the authors promote more molecular research to investigate the genetic diversity of the genus. This turns out crucial to determine the evolutionary relationships between Skierka species.