DEVELOPMENT OF SPORES AND CHARACTERS OF MYCORRHIZAE
OF THE GENUS KUKLOSPORA
Spores of species of the genus Kuklospora occur singly in the soil (Sieverding and Oehl 2006). They develop inside the neck of a sporiferous saccule at some distance from this saccule and originate from the neck and saccule contents. The sporiferous saccules originate terminally from or intercalary inside mycorrhizal extraradical hyphae by their swelling. Spores of the two species located in this genus, i. e., K. colombiana and K. kentinensis are globose to subglobose and coloured. Their subcellular structure consists of a 3-layered, coloured spore wall and two inner colourless germination walls. The outermost spore wall layer is colourless, sloughs with age, and is continuous with the wall of the sporiferous saccule neck. The second, structural layer of this wall consists of many coloured, tightly adherent, very thin sublayers (laminae). This layer occasionally develops towards the saccule, forming a stalk supporting the wall of the sporiferous saccule neck. The third coloured spore wall layer generally tightly adheres to the inner surface of the second layer of this wall and, hence, is difficult to observe.
The first inner germination wall consists of two adherent flexible to semi-flexible layers. The second germination wall is composed of three layers, of which the outermost one is ornamented with small granules (a beaded layer) and adheres to a plastic layer, highly thickening in lactic acid-based mountants. This layer stains intensively in Melzer's reagent. The innermost layer of this wall is thin and exceptionally difficult to reveal.
The first inner germination wall of spores of Kuklospora spp. starts to synthesize after the full differentiation of the spore wall and the completion of this germination wall precedes the beginning of the formation of the second inner germination wall. None of these walls has a physical contact with each other.
The two opposite pores formed at the beginning of the spore origination inside the neck of the sporiferous saccule are closed by the material building the two permanent spore wall layers after the full differentiation of the spore wall. In spores lacking the sporiferous saccules, two opposite cicatrices resembling small rings with a slightly raised border are visible.
In one-species cultures, both K. colombiana and K. kentinensis formed typical vesicular-arbuscular mycorrhizae intensively staining in trypan blue (Sieverding and Oehl 2006).
Kuklospora colombiana and K. kentinensis have originally been described as Entrophospora colombiana and E. kentinensis. The main arguments used to separate these fungi from Entrophospora and to transfer them to the newly erected Kuklospora, a sister genus of Acaulospora (Sieverding and Oehl 2006), have been (1) the formation of 3-walled spores by Kuklospora spp. as by Acaulospora spp., and not 2-walled ones as by Entrophospora spp., (2) the presence of a beaded layer in their innermost germination wall of spores identical to that synthesized in spores of most known species of Acaulospora in contrast to the relatively thick, coriaceous sensu Walker (1986), layer occurring in the inner germination wall of spores of Entrophospora spp., and (3) their higher phylogenetic relationship with members of Acaulospora than with E. infrequens, the only species of this genus of known molecular properties (Sieverding and Oehl 2006).
REFERENCES
Schenck N. C., Spain J. L., Howeler R. H. 1984. Several new and unreported vesicular-arbuscular mycorrhizal fungi (Endogonaceae) from Colombia. Mycologia 76, 685-699.
Sieverding E., Oehl F. 2006. Revision of Entrophospora and description of Kuklospora and Intraspora, two new genera in the arbuscular mycorrhizal Glomeromycetes. J. Appl. Bot. Food Qual. 80, 69-81.
Walker C. 1986. Taxonomic concepts in the Endogonaceae. II. A fifth morphological wall type in endogonaceous spores. Mycotaxon 25, 95-99.
Wu C.-G., Liu Y.-S., Hwuang Y.-L., Wang Y.-P., Chao C.-C. 1995. Glomales of Taiwan: V. Glomus chimnobambusae and Entrophospora kentinensis, spp. nov. Mycotaxon 53, 283-294.