Perennial ryegrass is naturally colonized by the endophyte fungus Neotyphodium
lolii. Spread of the fungus is achieved by vegetative growth of hyphae into the ovules of the host
so that dispersed seeds are already infected by the fungus. Studies on the anatomy of vegetative
organs of perennial ryegrass showed no influence of this fungus on plant anatomy. The aim of this
work was to compare the anatomy of the reproductive structures of Lolium perenne infected (E+)
and free (E-) of N. lolii. Seeds of L. perenne cv. Grassland Nui were sown in laboratory and
seedlings were checked for endophyte fungal infection. Inflorescences were harvested in different
flowering developmental stages and chemically fixed. The material was processed for light
microscopy study, stained with safranine-fast green and mounted in synthetic resin. Results suggest
that floral stem anatomy of infected plants and free of N. lolii were similar. Cross sections of Eand
E+ floral stems showed groups of chlorenchyma cells alternating with sclerenchyma in
subepidermal position and vascular bundles orderly located surrounding the central parenchyma.
Floret development was not affected by the fungus colonization. Endophyte was not observed in
stamens. Hyphae progressed from floral stem via rachilla to the base of gynoecium and invaded
ovary wall, ovule and nucellus. Hyphae were observed very close the embryo sac. Longitudinal
sections of endophyte free gynoecium showed numerous starch grains in the ovary cells, which
were not observed in the infected ovaries. In relation to seed formation, no anatomical differences
were found between caryopsis infected and free of endophyte contamination.