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Mycorrhiza News: The Quarterly Newsletter of Mycorrhiza Network (Discontinued from April 2023)
Vol.24(1)  April 2012
Print ISSN : 0970-695X

Centre For Mycorrhizal Culture Collection

Spores: The Solitary Morphotaxonomic signature for Arbuscular Mycorrhizal Fungi

Alok Adholeya: Director, Biotechnology and Bioresources, Centre for Mycorrhizal Research, The Energy and Resources Institute, New Delhi – 110 003 and
Chaitali Bhattacharya: Research Associate, Biotechnology and Bioresources, Centre for Mycorrhizal Research, The Energy and Resources Institute, New Delhi – 110 003
During our last issue in this section we provided our readers with the vital tips of generating and handling monosporal cultures of Arbuscular Mycorrhizal Fungi (AMF). While doing so, we emphatically emphasized that one of the important steps include the scrutinization and isolation of morphologically different spores for which we require the role of an expert researcher. In order to justify our point, we wanted to provide a point of view to our readers as to why do we consider the spores of AMF as its signature and feel that appropriate selection of these miniatures is a knack.

On morphological basis, there are certain important parameters of AMF that can assist us in identifying the organism till the genus level like presence or absence of arbuscule, alignment of intraradicular hyphae, presence of auxiliary cells, etc. But these vegetative structures are not used as bonafide identification feature because of their developmental pliability and variations within different host plants. The only structure which is found to be discrete and stable is our little asexual miniatures, ‘The Spores’. The spores, principally their walls, of a particular genus are found to be very specific in their structural and developmental pattern and hence, they are an important component of taxonomic description and phylogenetic analysis. Unlike other fungi, the spores formed by our AMF’s are found to be very large (up to 500 μm in diameter), they can be easily trapped and the structure can be analyzed using a simple stereo zoom microscope by an amateur. A good morphotaxonomist is one who would be able to analytically evaluate the spore and mark each and every distinct point of the sample under study. As all the spores look alike for a layman, it requires an additional effort to spot the difference and hence the conclusion that the researcher has to have a decisive and critical observatory knack!

Let us share some tips that should be kept in mind while observing these little creatures to help in becoming an expert like us! Do not restrict yourself to just the spore morphology analysis as other parameters like the mode of spore formation, the sub cellular structure of the spores, the germination pattern and the color of the spores do play an important role during the process of morphotaxonomic classification. While observing varied samples, you would appreciate that the spores are present in different patterns. In most cases the spores are present outside the roots, barring a few where the spores could be inside as well. The position and production of spores could be single, in loose aggregation or in a highly organized sporocarp. Our friendly advice to the readers would be to make it a point to tabulate all the characteristic features that are witnessed while observing the spores. You would realize in the end, that the final data created from your observation will invariably assist you in identification, at least till the generic level.

Concomitant morphological and molecular analyses have led to major breakthroughs in the taxonomic organization of the phylum Glomeromycota. As long as the identification was based on spore morphology, spore formation and spore wall structure, the classification was very uncomplicated but filled with enigma. However, as soon as molecular phylogenetic tools became available, they were included in taxonomic analyses and soon became the drivers of the establishment of a new taxonomy with many fanciful ‘new genera’. Although this article does not aim at explaining the taxonomic classification of AMF, which would be considered in our future editions, here we would provide you with the glimpses of some of the genera and its specific spore characteristics which can be noticed easily and assist amateurs in understanding the importance of spore in morphotaxonomic identification.

To begin with, in case of the genus belonging to the Glomeraceae family, it has always been seen that the layer of the spore wall is usually continuous with a wall of the subtending hypha and the surface of spores of Glomus spp. may be smooth (in most species) or differently ornamented. The spores are formed either outside or less frequently within the roots as single or in aggregates, in an unorganized hyphal matrix or in a highly ordered hypha. The presence of the internal spores may be a substitute for the vesicle. The spores are normally partitioned out from the hypha by different mechanisms like amorphous plug, a septum, an inner sub layer of the laminate layer of the spore wall or thickening of all sub layers of the laminate layer of the spore wall. This group has the widest variant of phenotypes and is considered to have numerous fungi among the entire Glomeromycota. Hence, it is considered the most confusing one for an inexperienced person. The spores are produced blastically at the end of a sporogenous hypha although intercalarily spore formation has also been reported

The typical feature of the Acaulosporaceae is the presence of soporiferous saccule seen during the origin of the spore. In this case, spores are formed terminally from the neck of this saccule which ceases to grow once the spore is formed. The spores are normally sessile and mostly produced singly. The two most important genera recognized in this family include Acaulospora and Entrophospora. Spores of fungi of the genus Acaulospora develop laterally from the neck of a sporiferous saccule. After the saccule has become fully expanded, a spore begins to develop from the side of the subtending hypha (termed “saccule neck”). As the spore matures, the saccule loses its contents and eventually degenerates hence it is often not attached to a fully mature spore. In case of Entrophospora, spores develop inside the neck of a sporiferous saccule directly or at a short distance from the saccule unlike Acaulospora.



For amateurs, Gigasporaceae is a delight since the spores are considerably large (>200μm). The most prominent feature is the presence of a bulbous sporogenous cell formed at the end of a fertile hypha connected with mycorrhizal roots, which is partitioned from the spore by means of a plug or, more rarely, by a septum. Two prominent genera include Gigaspora and Scutellospora. Apart from spores they also form clusters of auxiliary cells. They are echinulate with spines in case of Gigaspora but the auxiliary cells produced by Scutellospora spp. are smooth or knobby. One of the unique features of Scutellospora is the persistent germination shield associated with the innermost flexible wall of the spore. The mycorrhizae of Gigasporaceae spp. consist of only arbuscules; no vesicles are produced.





Archaeosporaceae and Paraglomaceae are very similar to the Acaulosporaceae and Glomeraceae. The only way of confirming and determining its identity would be by molecular sequencing of the small subunit 18s ribosomal DNA using specific primers. The genus includes Archaeospora as in Archaeosporaceae and Paraglomus as in Paraglomaceae. Archaeospora is a dimorphic fungus, forming both acaulosporioid and glomoid spores. Spores develop laterally, directly on the neck of a sporiferous saccule, and thus, they are sessile, similarly as most spores of the genus Acaulospora. One of the distinctive features while observing the vegetative characters is that the intraradical hyphae of the above mentioned fungi are with many coils present within and between the cortical cells and the hyphae has a patchy distribution along the roots. Similarly spores of Paraglomus are very similar to Glomus and the only visible difference is that it does not contain vesicles and their intraradical hyphae are frequently coiled within and between cortical cells unlike Glomus where the vesicles are very prominent and the hyphae is rarely coiled.

At the end, we are sure you would all agree to the fact that spores are indeed one of the most important components responsible for the taxonomic identification of Mycorrhiza hence they need to be analyzed with an investigative approach to reach the goal of classifying them.