|Welty Ronand E,|
Submitted to: Mycologia
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: January 23, 1995
Publication Date: N/A
Interpretive Summary: Tall fescue is a temperate-zone perennial tufted bunch grass which tolerates poor soils, temperature extremes and poor management practices. In the United States, it is grown on about 35 million acres for pasture, turf, and erosion control. In Oregon, tall fescue is intensely managed for seed production. The 1991 seed crop had a value of $54 million. The endophyte is a fungal symbiont of tall fescue. During drought-stress conditions, endophyte-infected plants can have increased growth and survival when compared to endophyte-free plants. Although this endophyte has been extensively studied, little is known about the fungus in the roots of its host. The purpose of this research was to determine: 1) if endophyte hyphae could be consistently recovered from the roots of endophyte-infected seedlings; 2) what effect does root growth media have on frequency of recovery and distribution of fungus in roots; and 3) what can be learned by observing fungal-root ultrastructure. Overall, 67% of all seedlings studied contained endophyte-infected roots. The rate of recovery was influenced by seedling age, growth medium used, and root type. In general endophyte was recovered from actively growing lateral roots. Electron microscopy revealed that the fungus grew throughout the epidermal region of the root but did not penetrate intact cells. Electron dense granules within the fungus contained high levels of phosphorus. These structures may act as phosphate reserves for use by the plant during nutrient stress. This is the first report on the presence of endophyte hyphae associated with the roots of tall fescue. This study provides a basic understanding of the frequency, distribution, and ultrastructural detail of endophyte in tall fescue roots.
Technical Abstract: Tall fescue has formed a mutualistic relationship with the fungal endophyte Acremonium coenophialum. Endophyte-infected (EI) plants can have increased growth and survival when compared with endophyte-free (EF) plants. Responses to endophyte infection vary and may be host-genotype and fungal-biotype specific. The mechanism(s) by which endophyte infection confers increased growth and survival is not understood. This research determined the occurrence, distribution, and ultrastructure of endophyte hyphae in the roots of axenically grown tall fescue seedlings. Acremonium coenophialum was recovered from excised roots of El seedlings grown on diverse agar media and from sterile coarse sand. Successful recovery of the isolate varied with seedling age, root type, and growth medium. Overall, sixty-seven percent of 218 EI seedlings contained endophyte in their roots. Root-fungal ultrastructure of agar-grown seedlings revealed epiphytic hyphae-bearing conidiophores with typical conidia and an electron-dense matrix that adhered hyphae to each other and to the root epidermal cell wall. Hyphae were found in regions previously occupied by root epidermal cells, but no direct penetration of intact cells was observed. Electron-dense granules within the fungal cytoplasm contained high amounts of phosphorous relative to adjacent tissues. This may benefit EI plants in low soil-phosphate conditions.