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Grazing Induces a Patterned Selection Response in Tall Fescue

Dep. of Agronomy and Soils, 202 Funchess Hall, Auburn University, AL 36849-5412

^* Corresponding author (evsanten{at}acesag.auburn.edu).

Pastures with perennial grass species are continuous in stands and are subjected to continual and often intensive natural selective forces. The objective of this study was to investigate the characteristics of tall fescue (Festuca arundinacea Schreb.) cultivars in response to natural selective forces. Ungrazed survivors from four cultivars—endophyte free (EF) GA-5, endophyte infected (El) GA-5, Johnstone, and KY-31—were collected randomly from four paddocks. These paddocks were then grazed at 2.50, 3.75, 5.00, and 6.25 animals ha–¹ for 2 yr and grazed survivors collected in similar fashion. These two groups were compared for four whole-plant, four tiller, and three flag leaf traits in a 2-yr study along with plants grown directly from the original seed lots. Each cultivar x age group x paddock combination consisted of 42 spaced plants. Each replicate of the original experiment was represented by seven plants selected at random from among the 10 originally collected from each replicate x paddock x entry combination. A polynomial response in grazed survivors was fitted with coefficients of determination ranging from 0.36 (maturity) to 0.79 (tiller number and dry matter yield). Comparison of GA-5 EF and GA-5 E1 revealed the influence of endophyte removal on host plants, which was more pronounced after grazing of the paddocks. Endophyte-infected grazed survivors were late maturing with longer and increased number of tillers and higher dry matter yields. The implications of this research for forage breeding are that (i) the seeded cultivar evaluated under grazing may be different from the original seed lot, and (ii) cultivars are dynamic entities that change over time.

Received for publication April 29, 1997.

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