Biodiversity, phylogeny and evolution of fungi

Abstract

India is rich in biodiversity. One-third of fungal diversity of the globe exists in India. The early fossil record of the fungi is poor, as unlike other organisms, fungal structures do not fossilize well. Thus, theories on phylogeny of fungi are based on the morphological features of the extant fungi. From the beginning of the 20th century fungi were proposed to be monophyletic, assuming that all the fungi were derived from an algal ancestor that lost its ability to photosynthesize. This gave rise to the flagellate fungi, from which rest of the fungi evolved. The loss of flagella and the evolution of zygospore gave rise to the Zygomycotina. The uninucleate zygospores of the Edogonales gave rise to the Ascomycota. The link between them being a fungus resembling Dipodascopsis (Ascomycota). The unicellular yeasts and complex filamentous Ascomycota members having extended dikaryotic stage evolved from it, believed to be similar to modern day Taphrina. This Taphrina-like ancestor was believed to have given rise to the ancestral Basidiomycota. Monophyletic origin of fungi was followed by most of the mycologists till 1960s. But, some mycologists proposed polyphyletic origin, with red algae as origin of Ascomycota. In late 1960s Oomycota was separated from the fungi. Slime molds were also separated into a different kingdom as well. Fungi were separated into two kingdoms: All the flagellate fungi were placed in kingdom Protista (including Chytridiomycota and slime molds) and the remainder in kingdom Myceteae. Hypothesis of phylogeny of fungi has changed radically with the advent of molecular techniques, ultrastructural and biochemical studies. On the basis of these studies in the late 1980s chytridiomycetes, zygomycetes, ascomycetes and basidiomycetes were included in kingdom Fungi. Oomycota, hyphochytrids, labyrinthulids, thraustochytrids and slime molds were accommodated in pseudo fungi. In 2007 a new classification of kingdom fungi-based on recent molecular phylogenetic analysis and morphotaxonomy was proposed, having one subkingdom – Dikarya and seven phyla. Recently in the 10th edition of Dictionary of the Fungi (2008) three kingdoms are accepted viz. Chromista, Fungi and Protozoa. True fungi belong to kingdom fungi having six phyla – Ascomycota, Basidiomycota, Chytridiomycota, Glomeromycota, Microsporidia and Zygomycota. The review contributes to the understanding of phylogenetic hypotheses, evolutionary relationships and circumscription of the fungi.