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Submitted to: Southern Nursery Association Research Conference
Publication Type: Proceedings Publication Acceptance Date: 10/1/2015 Publication Date: N/A Citation: N/A Interpretive Summary: The U.S. National Arboretum has an ongoing Hydrangea breeding program at its McMinnville, TN research site aimed at developing plants with improved bloom traits, frost tolerance, disease and pest resistance, and superior habit. One breeding method to discover novel combinations of traits is to look for offspring that fall outside the range of values of the parents, a phenomenon known as transgressive segregation. In order to find hydrangea plants with novel plant habit, we looked at transgressive segregation in three families of crosses that we made in 2010. All inflorescence and plant size traits showed some level of transgressive segregation. However, our results indicate that predicting transgressive segregation for specific traits is impractical; any trait may display transgressive segregation and the level of transgressive segregation is unrelated to heritability. Instead, certain crosses may be identified that increase the probability of seeing extreme traits in the offspring. These results will guide parental choice in experimental crosses with Hydrangea and provide germplasm for continued species improvement. Technical Abstract: Transgressive segregation occurs when trait values for offspring in experimental crosses fall outside (either above or below) the range of values recorded for the parents. Transgressive segregation is important to plant breeders as a source of novel or extreme traits. While widespread, it is difficult to predict which traits or parental combinations may be the most suitable for producing transgressive segregants. We have an ongoing hydrangea breeding program aimed at developing plants with improved bloom traits, frost tolerance, disease and pest resistance, and superior habit. The objective of this research is to evaluate the inheritance of inflorescence characteristics and plant size in related full-sibling families, determine the level of transgressive segregation present, and select full-sibling families for further species improvement. Controlled pollinations in 2010 produced a series of three Hydrangea macrophylla full-sibling families with similar genetic backgrounds, where each family had at least one parent in common. The Hydrangea macrophylla varieties ‘Princess Juliana’, ‘Trophee’, and ‘Zaunkoenig’ were used in the following crosses: ‘Princess Juliana’ x ‘Trophee’, ‘Zaunkoenig’ x ‘Princess Juliana’, and ‘Trophee’ x ‘Zaunkoenig’. In this study, the percentage of offspring with values more extreme than their parents ranged between 7% for height and 42% for stem width. An analysis of variance was performed to partition variation in transgressive segregation to sources attributable to trait and full-sibling family. While trait was not a significant source of variation (F = 1.3, p = 0.35), family did explain a significant portion of the variation in transgressive segregation (F = 3.5, p = 0.051). These results indicate that predicting transgressive segregation for specific traits is impractical; any trait may display transgressive segregation and the level of transgressive segregation is unrelated to heritability. Instead, certain crosses may be identified that increase the probability of seeing extreme traits in the offspring. |
