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Stability Indexes of Radiated and Nonradiated Oat Genotypes Propagated in Bulk Populations¹

Two lines of descent were established from an F₃ bulk lot of oats (Arena sativa L.) initiated by mixing seeds from 250 crosses. For one line of descent, seeds were radiated with thermal neutrons or X-rays from F₃ through F₆, and these treatments were followed by five generations of bulk propagation with no artificial selection. The other line was propagated for 10 generations with no artificial selection. Twenty random strains from each of four generations from the radiated (F₇, F₈, F₉, and F₁₁) and five from the nonradiated (F₃, F₆, F₇, F₈, and F₁₂) line of descent, and ‘Nodaway’ cultivar were used to measure stability indexes for grain yield, plant weight, harvest index, plant height, 100-seed weight, and seed numbers in the various generations.

Mean regression stability indexes for grain yield decreased from 1.17 to 1.02 in the nonradiated line, and increased from 0.82 to 1.04 in the radiated line of descent over time. Generally, data on oat strains from the radiated line fitted the linear regression model better than those from the nonradiated one. The changes in mean regression stability indexes for plant weight paralleled those for grain yield, but no trends in this statistic occurred for other traits.

Genotypic variances among strains within generations were sporadic for all traits in both lines of descent. for grain yield, seed number, and plant height there were consistent expansions in the genotype x environment interaction variances within generations. This was primarily due to the regression stability indexes among lines becoming more diverse over time. The contributions of deviations from regression to the interaction variance remained relatively constant over generations in both lines of descent.

Means and regression stability indexes for oat strains within generations were highly and positively correlated for grain yield, seed number, bundle weight, and plant height.

Key Words: Avena sativa L. • Fitness traits • Adaptation reaction

² Lecturer in Plant Science, University of Ife, Ife. Nigeria (formerly graduate student, Department of Agronomy, Iowa State University); and Professor of Plant Breeding, Iowa State University.

Received for publication February 20, 1974.