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Breeding for Rust Resistance in Orchardgrass by Phenotypic and Phenotypic-Genotypic Selection¹

Effectiveness of alternative selection methods is an important consideration in any plant breeding program. The purpose of this research was to evaluate recurrent phenotypic selection and selection based on both phenotypic performance and a polycross progeny test (phenotypic-genotypic method) for resistance to rust (Puccinia graminis Pers.) in ‘Sterling’ orchardgrass (Dactylis glomerata L.). Rust resistance was improved by each of three cycles of phenotypic selection. One cycle of phenotypic-genotypic selection (Cl-PG) achieved the same level of rust resistance and required the same length of time as did two cycles of phenotypic selection (C2-P). The mean rust rating of C1-PG and C2-P did not change with advancement from the first to the second generation; however, plant to plant phenotypic variation increased. Smaller phenotypic variances in both generations of C1-PG and C2-P than in Sterling suggested a decrease in genetic variance with selection; however, significant genetic variation was found in all derived populations. High parent clone-topcross progeny correlations indicated that progeny testing for rust resistance is unnecessary. The recurrent phenotypic selection method would favor maintenance of greater genetic diversity for resistance than the phenotypic-genotypic method because more plants could be selected in each cycle.

Key Words: Dactylis glomerata L. • Recurrent phenotypic selection • Phenotypic and genetic variance • Parent-progeny correlations

² Plant breeder, Cargill, Inc., Belmond, Iowa and professor of agronomy, Iowa State Univ., Ames IA 50011, respectively

Received for publication November 23, 1981.