Degree Type


Date of Award


Degree Name

Doctor of Philosophy




Four experiments were grown to evaluate competitive abilities of plant genotypes. The materials consisted of a set of early and a set of midseason oat (Avena sativa L.) isolines, a set of oat varieties, and a set with two barley (Hordeum vulgare L.) and three oat varieties. Plants of one genotype were sown in the center of each of paired hexagon plots with the tester plant which was grown in the center being surrounded by two rows of plants consisting of its own genotype in one plot and of another genotype in the paired plot;The oat isolines showed some evidence for overcompensation, whereas the oat varieties and oat and barley varieties were neutral with respect to competitive ability. Entries within a set were highly variable with respect to mean competitive reactions. The effects of competition were even more variable when individual pairs were compared. In the sets where isolines were grown, a large mean deviation for one entry most often was caused by an exceptionally large competitive advantage or disadvantage that occurred for only one paired comparison. When barley and oats were grown together in competitive stands, the competitive advantage or disadvantage shown by an entry tended to be consistent across all competitors;Competitive advantages or disadvantages displayed by oat and barley genotypes for biomass and grain yield were related to biomass or grain yield components. Increases in biomass and grain yield were reflected in significant increases in numbers of spikelets, primary and secondary florets, and tillers per plant. Competitive advantages and disadvantages were greatest in the interspecific comparisons.



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Bruce David McBratney



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97 pages