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Oat (Avena sativa L.) production has increased dramatically in the eastern Canadian prairies. The introduction of semidwarf oat cultivars to this region has resulted in the need for research regarding how a semidwarf oat performs relative to conventional tall oat cultivars. Split-split plot experiments were conducted at three site-years during 1999 and 2000 in Manitoba to examine cultivar responses of 'AC Ronald', a short-stature oat, and 'Triple Crown', a tall oat, under different crop rotations (grain legume or oilseed as a previous crop) and N fertilizer rates. Triple Crown had greater (P < 0.05) dry matter production than AC Ronald at anthesis (two of three sites) and maturity (one of three sites). At two of three sites, Triple Crown also displayed higher (P < 0.05) early season plant N uptake than AC Ronald, and Triple Crown always had higher (P < 0.05) kernel weight. However, averaged across sites, AC Ronald yielded 433 kg ha -1 greater (P < 0.05) than Triple Crown. Higher yield for the short-statured cultivar was attributed to greater (P < 0.05) panicle and kernel densities, and better assimilate partitioning (i.e., higher harvest index). Both cultivars were susceptible to lodging; however, Ha significant cultivar x site interaction indicated that under some conditions, AC Ronald experienced less lodging than Triple Crown. No significant cultivar effect was observed for evapotranspiration (ET) or water use efficiency (WUE). Both oat cultivars responded similarly to crop rotation and N fertilizer rate. While the grain yield advantage of AC Ronald appeared stable across treatment environments tested here, some differential cultivar responses for kernels per panicle and lodging resistance across sites were observed. This research supports an expansion of semidwarf oat production in the eastern Canadian prairies.

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.

Winter wheat (Triticum aestivum L.) cultivars produced in the semiarid environment of the Candian prairies are subjected to variable water stresses. Therefore, successful cultivars in this region require both a high production potential and yield stability. This study was initiated to compare the agronomic performance of two winter wheat cultivars that had demonstrated a differential response to the often high drought stress environment of Saskatchewan. Eleven field trials were conducted at seven locations in Saskatchewan from 1984 to 1987. Measurements included dry matter production, yield components, grain yield, harvest index, water use, and water use efficiency (...)