Mycologia 91: 776-782.
Genome sizes of Epichloë species and anamorphic hybrids.
Kuldau GA, Tsai H-F, Schardl CL (1999)
Several Neotyphodium species (asexual fungal symbionts of grasses) have been
characterized genetically as heteroploids (nonhaploids) derived by interspecific
hybridization involving sexual Epichlo?/i> species (Clavicipitaceae, Hypocreales).
Examples include Neotyphodium coenophialum with at least three ancestral Epichlo?/i>
species, and a rare endophyte of perennial ryegrass that appears to be a hybrid
of Epichlo?typhina with the common perennial ryegrass endophyte, Neotyphodium
lolii. In contrast, N. lolii appears to be haploid and closely related to Epichlo?festucae.
Hypothesizing that hybrid origins should result in larger genome sizes, we estimated
genome sizes for two Epichlo?/i> 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 Epichlo?/i> 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.