Date of Award


Document Type


Degree Name

Doctor of Philosophy (PhD)

First Advisor

Scott B. Milligan


Progeny testing is practiced to select the best crosses (families) prior to individual plant selection and to guide decisions relative to hybridizing and seedling planting in many crops including sugarcane (Saccharum sp. hyb.). Research to optimize the progeny testing methodology examined its effectiveness relative to family, within family, environment, replication, and intrarow plant spacing. Variance-component analysis indicated that family by environment (locations, years) interaction was a minor inhibitor of selection effectiveness. Within-family variance was the largest source of variation for the five traits considered. For stalk weight, stalk length, and stalk diameter, a small majority of this variance was due to genetic within-family plant-to-plant variation. Partitioning genetic from environmental plant-to-plant variation for plant weight and stalks per plant was not possible. Family by spacing interaction was not important. Genetic correlations of family means of the same trait at different spacings essentially equaled unity. Response to selection estimates indicated family selection among wider spaced families (82 cm between plants) was up to 31% more effective than family selection using narrow plant spacing (41 cm between plants). Since family by environment variances were minor compared to other sources of variation, effectiveness of testing was mostly a function of plant number and spacing. Replication across environments only marginally improved selection effectiveness. Predicted family gain demonstrated a 20 to 31% increase in selection effectiveness by using wider plant spacing. Repeatability values were higher in wide than in narrow spaced families. Stalk number was the least repeatable trait. Genetic mechanisms acting upon plant weight and its components were similar in each of the three environments. Phenotypic and genotypic path analyses direct effect coefficients were all positive and similar in magnitude indicating that selection for any plant weight component would result in an increase in plant weight. The relative efficiency of selection indices was higher when all plant weight contributing traits were included along with plant weight. Results from this study strongly suggest that family selection for plant weight and its components using widely spaced plants would be more accurate than selection using narrowly spaced plants.