Degree Type


Date of Award


Degree Name

Doctor of Philosophy



First Advisor

Irving T. Carlson


Studies by many researchers have shown that orchardgrass has lower dry-matter digestibility than other cool-season perennial grasses at comparable growth stages. Selection for higher digestibility could be done in the greenhouse under more controlled conditions than in the field. The main purpose of this research was to determine direct and correlated field responses to individual plant selection in the greenhouse for high and low in vitro dry-matter digestibility (IVDMD). Three hundred and twenty-five individual plants from a broad-based germplasm source were evaluated for IVDMD in the greenhouse. Twenty-two plants selected for high and 22 for low IVDMD were evaluated clonally in the field. The high IVDMD clones consistently averaged significantly higher in IVDMD than 22 low IVDMD clones. High IVDMD clones averaged significantly lower in dry-matter yield, half a day later in heading date, and they had wider and shorter leaves than low IVDMD clones. The two groups of clones did not differ significantly for plant height, panicle number, and leaf disease incidence;Four populations--High-5, High Cycle-1, Low Cycle-1, and Low-5--were formed from polycross progenies developed by intercrossing separately the high and low IVDMD clones. The High and Low Cycle-1 populations consistently averaged significantly higher and lower in IVDMD, respectively, than the base population. These responses were consistent over two stand densities and six harvests in two years. Responses to further selection on the basis of clonal performance in the field were inconsistent among harvests. Averaged over harvests and years, a significant response was obtained from further selection for low but not for high IVDMD;Derived populations did not show correlated responses for dry-matter yield, plant height, panicle number, and heading date. Consistent correlated responses did occur for leaf width. Both high IVDMD populations had significantly wider leaves than both low populations;This research indicates that significant improvement in IVDMD of orchardgrass can be obtained by selection in the greenhouse without sacrificing dry-matter yield.



Digital Repository @ Iowa State University,

Copyright Owner

Mohammad Jurial Rind Baloch



Proquest ID


File Format


File Size

145 pages