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Comparison of Inbred vs. Single-cross Testers and Estimation of Genetic Effects in Sunflower¹

The objectives of this study were to determine relative effectiveness of inbred versus single-cross testers in identifying combining ability of inbred sunflower (Helianthus annuus L.) lines; to determine whether epistasis was significant in the genetic systems controlling selected traits; and to evaluate the importance of additive and dominance variance for traits not influenced by epistasis. The hybrids evaluated in this study were formed by crossing the inbred lines RHA 274 and RHA 278, and their single-cross, RHA 274/RHA 278, to 10 randomly selected female inbred lines. The design used was a variation of the triple testcross, an extension of the Experiment III design.

The interaction of female x restorer parent was significant, indicating that the three testers did not rank the female lines identically for yield. However, the three testers did identify three of the top four lines when a 40% selection criterion was applied. For oil percentage, the interaction of female x male parents was nonsignificant indicating that the three testers gave very similar rankings. Utilizing any one of the three testers will differentiate or identify high-yielding potential female lines for yield and oil percentage in a population improvement or inbred development program.

Epistasis was a minor factor in the overall genetic variation for all traits studied in these sunflower lines. Additive variances were most important, with dominance variances important only for yield. The estimate for degree of dominance for yield (0.62) indicated that partial dominance predominated, an observation with significant implications for breeders in countries that primarily use open-pollinated cultivars. Improvement by development of high-yielding synthetics or open-pollinated cultivars should be continued. The results also indicate that breeders should develop population improvement schemes that utilize the large additive portion of genetic variance detected in this study.

Key Words: Helianthus annuus L. • Sunflower breeding • Genetic effects

² Research geneticist, USDA-SEA-AR; professor, Dep. of Agronomy; and research geneticist, USDA-SEA, AR, North Dakota State Univ., Fargo, ND 58105.

Received for publication April 21, 1980.

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