A new species of Periglandula symbiotic with the morning glory Ipomoea tricolor.

Abstract

Many morning glories (family Convolvulaceae) contain ergot alkaloids-important bioactive compounds produced exclusively by fungi. The ergot alkaloids of the few investigated morning glories are associated with the presence of a symbiotic Clavicipitaceous fungus. The genus Periglandula (Clavicipitaceae) was erected recently for two epibiotic species of morning glory symbionts. Biochemical and limited sequence data indicate that Ipomoea tricolor, a commonly cultivated morning glory from Mexico, contains a Periglandula species, but no signs of the fungus have ever been detected. Our goal was to isolate and describe this fungus, which we hypothesize represents a new species. Observation of fungal hyphae in evacuated seed coats of I. tricolor and subsequent transfer onto malt extract agar resulted in cultures of the symbiont isolated from the plant. The fungus grew slowly as white hyphae and sometimes aggregated into synnema-like structures, both of which lacked spores. We isolated sufficient DNA to sequence the genome with Illumina technology. Phylogenetic analyses based on multiple genes indicated that the symbiont of I. tricolor was distinct from, but related to, the two described species of Periglandula previously observed in other species of morning glories. Using quantitative polymerase chain reaction (qPCR), the fungus was quantified most abundantly in hypocotyls of I. tricolor, with lesser quantities in stems, cotyledons, and leaves. The fungus was not detected in roots, although ergot alkaloids were abundant in all tissues including roots. We conclude that the symbiotic fungus of I. tricolor is a distinct species of Periglandula and propose the name Periglandula clandestina, sp. nov.