Genome sizes of Epichloe species and anamorphic hybrids

Several Neotyphodium species (asexual fungal symbionts of grasses) have been characterized genetically as heteroploids (nonhaploids) derived by interspecific hybridization involving sexual Epichloe species (Clavicipitaceae, Hypocreales). Examples include Neotyphodium coenophialum with at least three ancestral Epichloe species, and a rare endophyte of perennial ryegrass that appears to be a hybrid of Epichloe typhina with the common perennial ryegrass endophyte, Neotyphodium lolii. In contrast, N. lolii appears to be haploid and closely related to Epichloe festucae. Hypothesizing that hybrid origins should result in larger genome sizes, we estimated genome sizes for two Epichloe and three Neotyphodium spp. Using quantitative Southern blot hybridization we estimated genome sizes of 29 ± 4 Mb for two sexual haploids, E. festucae isolate E189 and E. typhina E8. Estimates for hybrid anamorphs were 57 ± 7 Mb for N. coenophialum e19, and 55 ± 7 Mb for N. lolii X E. typhina Lp1. Electrophoretic karyotyping of these four isolates corroborated the genome size estimates. Also, the electrophoretic karyotype of N. lolii isolate e45 indicated a genome size similar to that of the Epichloe species, in keeping with the apparent nonhybrid nature of N. lolii. Genome size differences were reflected in the variation of conidium lengths and widths suggesting that large conidial size may be an indicator of heteroploidy and, therefore, possible hybrid origin of Neotyphodium species.