Water Relations of Standard Height and Dwarf Sunflower Cultivars.

Development of early maturing short stature sunflower (Helianthus annuus L.) cultivars followed the success of semi-dwarf cereals. Although a number of breeding programs have recently released dwarf sunflower cultivars for production in western Canada, the drought adaptability of dwarf cultivars has not been studied. Therefore, field studies were conducted under rainfed conditions at two Manitoba locations during 1994 and 1995 to compare seasonal water relations of 'Sunwheat-103' (SW-103), a dwarf hybrid, and 'AC-Aurora' (Aurora), a dwarf open pollinated cultivar, with 'IS-6111', a standard height hybrid. The dwarf hybrid, SW-103, experienced less stress (up to 0.44 MPa higher leaf water potential) than the standard height hybrid, IS-6111. Genotypic variation for osmotic adjustment was observed in both 1994 and 1995. SW-103 and Aurora respectively had up to 0.42 and 0.39 MPa lower osmotic potential at full turgor compared with IS-6111. Aurora displayed greater osmotic adjustment per unit decrease in leaf water potential than other cultivars. All cultivars maintained positive pressure potential during the study and whenever significant differences in pressure potential were observed, SW-103 usually had higher pressure potential than other cultivars. IS-6111 maintained higher photosynthetic rate and stomatal conductance than the dwarf cultivars. These results suggest that under conditions of adequate water supply, the tall hybrid had the highest productivity despite experiencing the lowest leaf water potential and osmotic adjustment. The drought tolerance advantages of shorter statured cultivars identified here may be more important to productivity maintenance under limited soil water conditions.