Critical water potentials for germination of wheat cultivars in the dryland Northwest USA

Low soil water potential limits or prevents germination and emergence of rainfed winter wheat (Triticum aestivum L.). This phenomenon is particularly pronounced in the winter wheat-summer fallow region of the US Inland Pacific Northwest, where wheat is routinely sown deep to reach moisture with 12-15 cm of soil covering the seed. Wide differences in seedling emergence among winter wheat cultivars have been reported, but few previous experiments have examined germination differences among cultivars as a function of water potential. The objective of our laboratory study was to quantify seed germination of five commonly sown winter wheat cultivars (Moro, Xerpha, Eltan, Buchanan and Finley) at seven water potentials, ranging from 0 to -1.5MPa. Germination was measured as a function of time for a period of 30 d. At higher water potentials (0 to -0.5 MPa), all cultivars had germination of more than 90%. At the lowest water potentials (-1.0 to -1.25 MPa), however, Moro consistently exceeded the other cultivars for speed and extent of germination, with total germination of 74% at -1.0 MPa and 43% at -1.25 MPa. Since its release in 1966, Moro has been sown by farmers when seed-zone water conditions are marginal. Scientists have long known that coleoptile length is an important factor controlling winter wheat seedling emergence from deep sowing depths. In addition to having a long coleoptile, our data suggest that Moro's known excellent emergence ability from deep sowing depths in dry soils can also be attributed to the ability to germinate at lower water potentials than other cultivars.