A comparison of genetic information from open-pollinated and control-pollinated progeny tests in two eucalypt species

Abstract

Genetic-parameter estimates and parental breeding-value predictions were compared from open-pollinated and control-pollinated progeny populations of Eucalyptus globulus and two populations of E. nitens. For E. globulus there were two types of open-pollinated populations (native stand open-pollinated and seed orchard open-pollinated) and two types of control-pollinated populations (intra-provenance and interprovenance full-sib families). For E. nitens there were two populations, a seed orchard open-pollinated population and intra-provenance full-sib families. Progeny tests were established across multiple sites and 2-year height and diameter were measured and volume calculated. Genetic parameters from native stand open-pollinated E. globulus were unlike the parameters from the other three E. globulus populations; heritability estimates were severely inflated, presumably due to high levels, and possibly differential levels, of inbreeding depression relative to the other populations. Estimates of dominance variance in the E. globulus full-sib populations were high, but were zero in the E. nitens population. Correlations among parental breeding values, predicted using data from the different populations, were generally low and non-significant, with two exceptions: predictions from the two E. globulus full-sib populations were significantly correlated (r=0.54, P = 0.001), as were predictions from the E. nitens seed orchard OP and full-sib population (r = 0.61, P = 0.08). There was some indication that superior parents of E. globulus native stand open-pollinated families also tended to have above-average breeding values based on the performance of intra-provenance full-sib offspring. The consequences of these results for exploitation of base-population collections from native stands are discussed.

An investigation of assumptions made in estimating genetic parameters and predicting genetic gain in a Eucalyptus nitens breeding programme in South Africa

“…Although a coefficient of relationship of 0.4 has been used for eucalypts (Brawner and Elizaul 2007;Greaves et al 1997;Volker et al 1990;Whiteman et al 1990), this coefficient of relationship supports earlier work by various authors (Griffin and Cotterill 1988;Griffin et al 1987;Hodge et al 1996;Verryn 1993), where it was suggested that seed orchard OP families are not true half-sib families, and may contain Molecular marker studies will further inform the levels of selfing in this population, and whether the levels of inbreeding are variable or more uniform.…”

“…The authors also investigated the effect of provenance in variance component estimation, i.e., families nested within provenance (family (provenance)) and families across provenances (Swain et al 2013b), but as this and other studies have shown that across-provenance estimates result in overestimates of additive genetic variance (Brawner and Elizaul 2007;Johnson 1996;Tibbits and Hodge 1998), this scenario was not included in this report. The scenarios investigated were: 1) Coefficient of relationship and outcrossingFollowing the approach of Squillace (1974), and extending his calculations, it has been shown that 30% selfing gives an average coefficient of relationship among open-pollinated (OP) progeny of 0.4 (Griffin and Cotterill 1988) and 25% selfing gives an average coefficient of relationship of 0.5 (Hodge et al 1996). Snedden et al (2007) assumed a coefficient of relationship of 0.33 in an E. grandis study where approximately 20% inbreeding was found.…”

“…The species demonstrates preferential outcrossing and appears to have a late-acting selfincompatibility system operating to reduce the production of selfed seed (Pound et al 2003;Tibbits 1989). The assumption of > 70% outcrossing made by many authors (Butcher and Williams 2002;Grosser et al 2010;Hodge et al 1996;Moncur et al 1995;Moran et al 1989), may not be true of these F1 E. nitens seed orchards, due to poor flowering.…”

“…However, these flowering windows do overlap (Gardner 2003;Jones 2002), which may allow for panmictic pollination some of the time. In addition to asynchronocity, flowering in E. nitens is subject to seasonal influences (Gardner and Bertling 2005;Jones 2002;Moncur and Hasan 1994;Tibbits 1989) and, as the stability, or greater influence, of female effects in reproductive success in some eucalypts has been noted (Leal and Cotterill 1997;Suitor et al 2009;Tibbits 1989), it is possible that only a few effective males may contribute to pollination of all the other trees in a seed orchard (Hodge et al 1996;Suitor et al 2009;Swain et al 2013a). Conversely, pollen from a few heavy-flowering individuals may have too large a genetic influence on adjacent female trees (Moncur and Boland 2001).…”

“…It has been 1 Gardner RAW. 2012 (Hamilton et al 2008;Hodge et al 1996), but if non-additive effects were playing a role, the predictions of genetic gain would be overestimated due to inflation of narrow-sense heritability estimates (Bush et al 2011;Hodge et al 1996). Therefore, to determine which assumptions best fit the ICFR E. nitens populations for the estimation of genetic parameters in the F1, several scenarios of predicted genetic gain were developed from the F1, and compared with the gains realised from genetic gain trials (F2).…”