Investigating the heritability of figure in poplar
by Youran Fan, FNR Graduate Research Assistant
Figure, as a wood characteristic, can be used in wood identification and can add extra value to wood products. Understanding the heritability is important to the reliable production of figure-wood products that can meet industrial standards. With this in mind, colleagues and I have used microsatellites to identify a 25-yearold male hybrid aspen named “Grober,” as a Populus x canescens (P. alba x P. tremula). More than 80 “Grober” propagules from the original parent tree were sampled at various times (7, 11, 12, and 60 months) after growth under two environmental regimes (field vs. greenhouse) and following two treatments (pruned vs. unpruned).
All “Grober” propagules exhibited figure in all woody parts. By splitting the wood longitudinally, the figure was identified as an undulating pattern on the radial surface. These results were not observed in the control group, which included two P. alba genotypes (A502 and 4877), a second P. x. canescens clone (Ca-2- 75), “Crandon” (P. alba x P. gradidentata), and “Sherrill” (P. alba x P. grandidentata). The control group showed only smooth radial surfaces with straight grain. Unlike the control group, “Grober” propagules clearly exhibited a constant spirality (2.62 ± 0.12 degrees/cm) to axial growth in 11-month-old plantlets. However, this spiral growth pattern was not apparent in wood produced by the mature, parent tree from which the plantlets were derived. In addition, veneers cut from the same 25-year-old “Grober” tree appeared to produce a type of figure that had not yet been named. Based on its appearance, we decided to call it Scatter Moiré.
To investigate chemical signals that may be involved in figure formation, 160 grafts were made between “Grober” and various non-figured aspens. After sampling this population, we concluded that graft-transmissible signals are not involved in figure formation in “Grober.” Additionally, “Grober” was crossed to A502 to test the inheritance of the gene responsible for figure formation. More than 2,000 seedlings were obtained. A sub-sample of this population revealed that 79 out of 377 seedlings exhibited figure. A Chi-square test led to the rejection of a 1:1 segregation ratio between figure and non-figure phenotypes, but not a 1:3 segregation ratio. Overall, these analyses showed that figure in “Grober” is under genetic control, but the inheritance pattern may not be simple.