AN ABSTRACT OF THE THESIS OF MONCEF MOHAMED HARRABI for the degree of MASTER OF SCIENCE

approved: Willis L. McCuistion Four winter and four spring barley cultivars along with their F1 hybrids were grown on the Hyslop Agronomy Farm near Corvallis, Oregon, a high rainfall site (over 1000 mm annually) located in the Willamette Valley. The experiment consisted of four replications. Ten seeds of each F 1 and parents were seeded in a three meter row. Plants were spaced 30 cm between and within the rows. Investigations were made to evaluate the presence of hybrid vigor when hybridizing winter and spring barley. Gene action estimates contributing to yield and its components were obtained. Additional information concerning the inheritance and the association of 12 agronomic traits and yield were also evaluated. The data were analyzed by using the factorial technique, analysis of variance, correlations, path-coefficient, parent-progeny regressions, and by polynominal and multiple regressions. The traits measured were: (1) total yield per plant, (2) kernel weight, (3) tiller number per plant, (4) kernel number per spike, (5) heading date, (6) plant height, (7) flag leaf area, (8) flag leaf width, (9) flag leaf length, (10) culm diameter, (11) head length, and (12) head extrusion. Heterobeltiosis was observed in all of the hybrids except in the cross between Adair and Short Wocus. The absence of hybrid vigor in this cross may be attributed to the fact that these two parents are closely related. Combining ability analysis as well as narrow sense heritability estimates indicated that additive gene action is more predominant in the expression of heading date, plant height, tiller number, head length, culm diameter, flag leaf width and kernel weight. Heterobeltiosis and high SCA estimates were observed in most of the hybrids for yield per plant and kernel number per spike. This implies that most of the genetic variation associated with these two traits resulted from non-additive gene action. The high SCA estimate observed for head extrusion indicates that this trait appeared to be controlled by non-additive gene action. Both additive and nonadditive gene action are important for the expression of flag leaf area and flag leaf length. When the 12 traits were correlated and the r values partitioned into direct and indirect effects it was observed that tiller number, kernel weight and kernel number per spike exerted the highest direct effect on yield. Plant height had a small positive direct effect, but an indirect effect on yield through kernel weight. It was further observed that a negative association exists between tiller number and kernel weight. This indicates that, in this barley population, it would be difficult to select for a plant containing large grain type and short stature, but it may be easy to select short plants with a relatively large number of tillers and high kernel number per spike. Path coefficient analysis indicated further that flag leaf area has a negative direct effect on yield and the remaining six traits have a negligible or no direct effect on yield, indicating that these traits can not be used as selection criteria. More genetic variability for tiller number and kernel number per spike was noted in the winter barley while more genetic variability for kernel weight was found in the spring barley. The results of this study suggest that increases in yield could be achieved by selecting plants with relatively high tiller number and high kernel weight. Selection for a high kernel number per spike can be accomplished by selecting for large culms and longer peduncle. By this procedure the breeder can take advantage of the additive genetic variance associated with tiller number and kernel weight and by the positive correlation that exists between culm size and peduncle length with kernel number per spike. Estimates of genetic variance and heterosis in F 1 winter x spring barley crosses (Hordeum vulgare, L.)