Genetic Variances for Forage Yield in Crested Wheatgrass at Six Levels of Irrigation

Abstract

Rangelands in the western USA are characterized by extreme seasonal and site variations in soil moisture and extended periods of severe water deficit. Development of improved germplasm that is productive over a wide range of soil moisture conditions is a major objective of forage breeding programs in this region. Ample levels of heritable genetic variation are prerequisites for genetic progress in any breeding program. Although expression of genetic variability among breeding lines is known to decrease in some species as water becomes limited, neither this relationship nor the stability of genetic responses at different water levels have been studied in crested wheatgrass, Agropyron desertorum (Fisch. ex Link) Schult. A linesource sprinkler system was used under a field rainout shelter to evaluate the dry matter yield of 29 clonal lines of crested wheatgrass at six levels of water application. Forage yield declined linearly from optimum water levels to levels representative of severe drought. Broad‐sense heritability values along with the range and genetic variance among clonal lines also declined markedly as water application decreased. Experimental error, as reflected by the coefficient of variation, was substantially larger under drought than at higher water applications. Although the clone ✕ water level interaction was significant (P < 0.01), positive and significant (P < 0.01) Spearman correlation coefficients indicated a relatively high degree of consistency among clones at different water application levels. Results indicate that this tetraploid population of crested wheatgrass has sufficient genetic stability to permit selection for forage dry matter yield at water levels substantially above the target level.