Seasonal availability of water is a major consideration in the management a
nd selection of plant materials for irrigated pastures in the Intermountain
West, USA. Objectives were to evaluate the forage field of 10 tall fescue
(Festuca arundinacea Schreb.) strains and cultivars across five irrigation
levels and fo elucidate the effects of the endophytic fungus Neotyphodium c
oenophialum (Morgan-Jones & Gems) Glenn, Bacon & Hanlin an productivity and
trends. a differ-source irrigation system was used in a 2-yr study, Signif
icant differences were detected among the fan fescue entries for dry matter
yield (DMY), and differences were relatively consistent across wafer level
s (WL) as indicated by the nonsignificant cultivar x WL interaction and sig
nificant correlations among WL. Trends in DMY across WL were largely curvil
inear; however, linear bends were much more predominant during the late sum
mer and fall. Stability parameters, based on regression of cultivar x WL X
year means on their respective WL x gear means, differed among cultivars in
analyses including all harvests but were relatively uniform (b approximate
to 1.0) for most cultivars later in the season. Differentes in DMY between
'Ky 31' tall fescue infected with the Neotyphodium endophyte and its endop
hyte-free counterpart confirms earlier reports of the positive effect of th
is fungal organism on forage yield in fall fescue, particularly in water-li
mited environments. Seasonal distribution of yield was primarily determined
by water availability during the late summer and fall. The relative consis
tency in DMY of the cultivars across WL indicates that annual yield average
d across levels of wafer stress mould be a logical criterion for selection
of germplasm for irrigated pastures in the Intermountain Region.