No abstract

The cold resistance of 18 varieties of winter wheat hardened in a growth chamber was studied at various stages of development and the tesults were compared with the field survival of these varieties.In the Ero',vth chamber two maxima of cold resistance vrere found, the first for the?ry or freshly moistened seed and the second rvhen plants had.approxi--mately 4 to 6 leaves. Varietal difercnces v'ere found in thc exact timing of this second maximum and in its duration. As a result, some varieties changed their rank for cold resistance as they developed.Partial asreement was observed betrveen the field survival of varieties sown at difierenidates and the changes in cold resistancc of these varieties as thcy developed in the growth chamber.

The relationship between plant height, competitive ability and yield performance was examined for six cultivars of winter wheat (Triticum aestivum L. era. Thell.) in southern Alberta. Competition significantly reduced grain yield, heads.m -2 and kernels.m -2. Competition also reduced heads.plant-1 and kernels.heM-[ but did not affect plants.m -2 or kernel weight. For yield and other area-based yield components, multiple regression showed that interference by competitors was increased by reducing the height of the neighbouring cultivar and by increasing both competitor height and the ratio of competitor height to cultivar height. Intensities of yield interference in pure stands of the six cultivars were predicted by substituting their height into this multiple regression model. These predictions showed a one-to-one relationship (b = 1.01; p < 0.01; R 2 = 0.85) with pure stand grain yields, indicating that reduced inter-plant interference is a yield-positive trait that is inevitably present in high yielding cultivars. For plant-based yield components (heads.plant-i, kernels.head-1 and kernel weight), cultivar-specific compensation between traits maintained a balance between the number and the size of heads and kept kernel weight constant. These responses to optimize the development of viable kernels modified or obscured the effect of competition.

Significant levels of heterosis were demon-sis resulting from hybridization of genetically strated in F yield trials from crosses between diverse spiing anci winter types." To ouithree spring_and three win_ter wheats (7. aesti-knowledg6 thii is the f,rst pubdJhed repo.roi yym -L.): -Thatcher X Winalta, Cypress y heterosis" for yield in f'. fryUriO, tii*."n Slrq*ou 22 MC, and Lee X Cheyenne. spring and winter wheat cultivars. This in_ Yrelcls up to 4O7o higher than those of the formation has significance in both hybrid spring wheat parent were attributed to hetero-wheat and convenlional breeding ptog.u-..

Yield and protein content of 100 random selections from single crosses of wheat and barley were determined for three years. Results of each test showed highly significant differences in yield and protein content of selections. There was a highly significant negative correlation between yield and protein content in each test, the values for rpy varying from −.483 to −.806. In general, the relationship was improved when mean values from several tests were correlated. The behavior of individual selections under a wide range of environmental conditions was relatively constant even though wide differences occurred in both yield and protein content of individual selections.