Seed transmission of an exotic endophyte in tall fescue

Endophyte strains have been identified which may enhance plant growth and resistance to stress but not produce the major alkaloid toxins which impair livestock health and productivity (Fletcher and Easton 1997). Strains identified in exotic germplasm are introduced to adapted grass cultivars by inoculation and seed is taken from infected plants. This seed must be multiplied for at least two more generations for commercial release of the cultivar-endophyte association (Rolston 1993). Efficient transmission of endophyte to seed is essential (Fletcher and Easton 1997). An 85% transmission rate, for example, compounded over three generations, would lead to only 61% infection. Endophyte hyphae extend with the elongating stem and infect the developing inflorescence and the ovules. Philipson and Christey (1986) observed infection of the developing seed of perennial ryegrass as early as the "notch" stage of the embryo; but White et al. (1991) reported that the embryo of Festuca spp was not infected until fully differentiated. Transmission of endophyte to seed of naturally infected perennial ryegrass is usually assumed to be close to 100%. Endophyte-free tillers may occur on infected tall fescue plants (Hinton and Bacon 1985). Percentage infection of tall fescue seed from verified infected plants may vary (Welty and Azevedo 1993), and infected and uninfected maternal half-sibling seedlings occur within a naturally infected tall fescue breeding pool (Easton, unpublished). Synthetic associations, lacking prolonged selection for mutual adaptation, may not necessarily be efficiently transmitted. A synthetic tall fescue association was examined to determine the frequency of transmission.