Influence of Water Deficits on the Water Relations and Growth of Echinochloa turneriana, Echinochloa crus-galli, and Pennisetum americanum

Abstract

Echinochloa turneriana (Domin) J. M. Black (Channel millet) is a wild grass native to the arid Channel Country of inland Australia, where it is used as forage and hay. In its native habitat flooding induces germination, and the plant can complete its life cycle with this single watering. The present study was conducted to gain a better understanding of the mechanisms which allow Channel millet to develop from germination to harvest with a single watering. Channel millet's drought resistance was compared with that of Pennisetum americanum (L.) Leeke (pearl millet), an important drought-resistant crop, and Echinochloa crus-galli (L.) Beauv. var. oryzicola (Vasinger) Ohwi (oryzicola), an obligate rice field weed. Plants of each species were grown under well-watered (control) and droughted conditions under long days in a greenhouse and under long and short days ifi a growth cabinet. Under long days, control and droughted Channel millet plants flowered before controls of pearl millet and oryzicola. Under long days and droughted conditions in the greenhouse flowering was delayed, and plant height, shoot dry weight, panicle number and tiller number were decreased in each species. Active osmotic adjustment under drought was detected in pearl millet by the pressure-volume and expressed sap methods, but was not observed in the other two species. The bulk modulus of elasticity decreased (cell wall elasticity increased) significantly under drought in Channel millet, but not in pearl millet or oryzicola. The apoplastic water volume was about 20% for all species and treatments. This study suggests that Channel millet's rapid development is important in helping the plant to complete its life cycle before the onset of a severe water deficit. Once severe water deficits develop, no osmotic adjustment occurs in Channel millet, and turgor is significantly decreased despite a decrease in the bulk modulus of elasticity.