Salmacisia, a new genus of Tilletiales: reclassification of Tilletia buchloeana causing induced hermaphroditism in buffalograss

摘要

For 119 y the fungal parasite Tilletia buchloeana has been known to induce female sex organs (pistils) in male plants of buffalograss, making them hermaphrodite. Here we report the life cycle characteristics and phylogeny for T buchloeana based on morphology and large subunit region of nuclear ribosomal RNA gene (nLSU-rDNA) to accurately place pistil smut within order Tilletiales. We found that T. buchloeana induces hermaphroditism in not only male sex forms of buffalograss by inducing the development of otherwise vestigial pistils but also in female sex forms by inducing hypertrophy of otherwise vestigial stamens (male sex organs). The fungus also induces the development of additional pistillate flowers in both infected male and female plants. Due to its pistil inducing effects we refer to T. buchloeana as pistil smut. Pistil smut exhibits a combination of morphological and life cycle characteristics that are unique among species of order Tilletiales. Phylogenetic analyses of nLSU-rDNA sequences using maximum parsimony, maximum likelihood and genetic distance-based methods show that pistil smut exhibits an elevated rate of nucleotide substitution and is as, or more, distant from Tilletia species than the basal group Erratomyces patelli. As such pistil smut occupies a phylogenetic position outside the current taxonomic circumscription of genus Tilletia. Therefore a new Latin binomial combination Salmacisia buchloeana is proposed as a sister taxon of Tilletia to accurately describe the phylogenetic position of pistil smut.