Population Differentiation, Spatial Variation, and Sampling of Tall Fescue under Grazing

Abstract

Tall fescue [Festuca arundinacea Schreb.] is the most important cool‐season perennial forage grass in Alabama and the southeastern USA. Genetic variation is essential for breeding improved cultivars, and understanding factors influencing genetic variability in pastures is important if material from existing pastures is to be used in a breeding program. This study was conducted to determine the extent of differentiation for agronomic traits in pastures grazed long‐term and to investigate possible spatial variation and its effect on sampling. Three populations from permanent pasture treatments of the USDA SARE cropping system trial in Virginia were sampled: (i) pure tall fescue fertilized with N, stocked continuously (Fescue + N); (ii) tall fescue–alfalfa (Medicago sativa L.) mixture used as hay and pasture (Fescue + alfalfa); and (iii) tall fescue–red clover (Trifolium pratense L.) mixture used as hay and pasture (Fescue + red clover). The tall fescue cultivar was endophyte‐free Ky 31 [fescue endophyte: Neotyphodium coenophialum; syn. Acremonium coenophialum]. Plants from these paddocks were established in central Alabama in 1995. Original seed from the SARE trial were also germinated for establishing the original population. Ex situ evaluation was conducted in Alabama (1995–1997). Compared with plants derived from the original seed lot, plants derived from pastures under grazing had significantly earlier maturity, higher dry matter (DM) yield per plant, and larger plant diameter, indicating population differentiation in response to grazing. No significant differences were observed among populations with different pasture management treatments. Statistical and graphical analysis of spatial variation of agronomic traits showed no spatial relationships in any of the six sampled paddocks. Bootstrap estimates of minimum and maximum values indicated that 25 individuals per paddock captured most of the phenotypic variation within each paddock. A random walk approach covering the entire unit being sampled seems therefore to be an appropriate strategy for sampling similar pastures to obtain base material for a breeding program.