Distribution, spore ontogeny and host reactions in Acaulospora scrobiculata (Diversisporales)
Muthukumar, T. Damodaran
Acaulospora scrobiculata is distributed in different vegetation and soil types in Tamil Nadu, India, and proliferates in different plant species, but distribution and abundance of its spores were not influenced by soil properties. A. scrobiculata inhabits different plant species including cowpea [Vigna unguiculata (L.) Walp.], maize (Zea mays L.), sorghum (Sorghum vulgare L.), Tephrosia (Tephrosia purpurea Pers.) and sunnhemp (Crotalaria juncea L.). Spores were produced in a soil-sand mixture five to nine weeks after spore inoculation. Under sorghum spore production was maximal, while minimum sporulation was observed under sunnhemp. Sporogenesis starts with the differentiation of the sporogenous hyphae terminally along thin-walled coenocytic hyphae. The terminal part of the sporogenous hyphae swell as a sporiferous saccule primordium, which matures into a sporiferous saccule delimited by a septum in the lower channel of the stalk. The spore is produced laterally within the stalk of the sporiferous saccule. The cytoplasm in the sporiferous saccule stalk differentiates into regions of high and low density prior to spore primordium initiation. The spore differentiates laterally in the stalk and expands. After complete spore differentiation, a second septum is formed delimiting the terminal portion of the sporiferous saccule, which degenerates leaving a single scar. Direct germination of the sporiferous saccule without spore formation is reported for the first time in the Acaulosporaceae (Diversisporales).