Genetic parameters of Abies alba progenies from seed orchards and natural populations in Romania

Abstract

A total of 204 silver fir open-pollinated families from four first-generation seed orchards and 12 natural stands were tested in a nursery experiment. The performances and genetic parameters of the seed orchards (SO) and natural populations progenies (NP) were determined and compared at ages from 3 to 6 years old. Several traits were assessed such as: the total height, the annual height increment, the root collar diameter, the branch length, the number of branches, and the bud burst evaluated during spring 2015-2016.
On average, progenies derived from seed orchards outperformed those from natural stands, exhibiting 8–14% greater height and 4–6% greater diameter. Estimates of genetic variance components indicated that most of the variation was attributable to additive genetic effects. Total height and annual height increment showed the highest proportions of additive variance, ranging from 42 to 91% in NP progenies and from 41 to 78% in SO progenies.
Narrow-sense individual heritability estimates were generally higher than those previously reported for silver fir, ranging from 0.12 to 0.83 for SO progenies and from 0.23 to 0.91 for NP progenies. Family heritability exceeded individual heritability in both progeny types investigated. Among the studied traits, total height exhibited the highest heritability for both progenies. Heritability of total height increased moderately from ages 3 to 6, whereas heritability for root collar diameter declined and remained relatively stable for branch-related traits.
Phenotypic and genetic correlations between growth traits were relatively high, while those between bud burst and growth traits were positive and weak for both progenies. The correlations between growth traits and branch traits were positive but nonsignificant. A significant correlation was obtained between bud burst in 2016 and elevation of populations. The phenotypic correlations were higher than the genetic ones for both progenies.
Genetic gain differed depending on the selection method, intensity, and traits examined. Across all selection methods, total height showed greater genetic gain than root collar diameter. Recurrent selections based on the parental genetic values will bring the greatest genetic gain in the next breeding generation. The genetic gains that could be achieved if the backwards selection will be used at the level of the first-generation seed orchards are between 19–27% for total height, 9–27% for diameter and 40–48% for current height increment. If the backward selection is used in natural populations, a genetic gain of 21–32% for total height, 13–22% for diameter and 42–55% for current height increment could be obtained. The results are discussed linking them to their implications for the development of a silver fir breeding strategy and also for the second-generation seed orchards establishment.