Reciprocal and advanced generation hybrids between Corymbia citriodora and C. torelliana: forestry breeding and the risk of gene flow Geoffrey Dickinson, Helen Wallace, David Lee To cite this version: Geoffrey Dickinson, Helen Wallace, David Lee. Reciprocal and advanced generation hybrids between Corymbia citriodora and C. torelliana: forestry breeding and the risk of gene flow. Annals of Forest Sci- ence, Springer Nature (since 2011)/EDP Science (until 2010), 2012, 70 (1), pp.1-10. 10.1007/s13595- 012-0231-2. hal-01201452 HAL Id: hal-01201452 https://hal.archives-ouvertes.fr/hal-01201452 Submitted on 17 Sep 2015 HAL is a multi-disciplinary open access L’archive ouverte pluridisciplinaire HAL, est archive for the deposit and dissemination of sci- destinée au dépôt et à la diffusion de documents entific research documents, whether they are pub- scientifiques de niveau recherche, publiés ou non, lished or not. The documents may come from émanant des établissements d’enseignement et de teaching and research institutions in France or recherche français ou étrangers, des laboratoires abroad, or from public or private research centers. publics ou privés. Annals of Forest Science (2013) 70:1–10 DOI 10.1007/s13595-012-0231-2 ORIGINAL PAPER Reciprocal and advanced generation hybrids between Corymbia citriodora and C. torelliana: forestry breeding and the risk of gene flow Geoffrey R. Dickinson & Helen M. Wallace & David J. Lee Received: 16 April 2012 /Accepted: 27 July 2012 /Published online: 17 August 2012 # INRA / Springer-Verlag France 2012 Abstract the style and reduced numbers of ovules penetrated by & Context Corymbia F1 hybrids have high potential for pollen tubes. Reproductive isolation was weakest within plantation forestry; however, little is known of their repro- the C. citriodora subsp. citriodora maternal taxon, with ductive biology and potential for genetic pollution of native two hybrid backcrosses producing equivalent capsule and Corymbia populations. seed yields to the intraspecific cross. & Aims This study aims to quantify the influence of repro- & Conclusions High hybridising potential was identified ductive isolating barriers on the success of novel reciprocal between all Corymbia species and F1 taxa studied. This and advanced generation Corymbia hybrids. provides opportunities for advanced generation hybrid & Methods Two maternal taxa, Corymbia citriodora subsp. breeding, allowing desirable traits to be amplified. It also citriodora and Corymbia torelliana, were pollinated using indicates risks of gene flow between plantation and native five paternal taxa, C. citriodora subsp. citriodora, C. torelli- Corymbia populations. ana,oneC. torelliana × C. citriodora subsp. citriodora hybrid and two C. torelliana × C. citriodora subsp. variegata hybrids. Keywords Corymbia . Hybrid . Backcross . Isolation . Pollen tube, embryo and seed development were assessed. Genetic pollution . Gene flow & Results Reciprocal hybridisation between C. citriodora subsp. citriodora and C. torelliana was successful. Advanced generation hybrids were also created when C. 1 Introduction citriodora subsp. citriodora or C. torelliana females were backcrossed with F1 hybrid taxa. Prezygotic reproductive Corymbia (Myrtaceae), comprising over 113 tree species, is isolation was identified via reduced pollen tube numbers in a sister genus to Eucalyptus and is a major component of tropical and subtropical woodland and forest floras across Handling Editor: Bruno Fady northern Australia (Hill and Johnson 1995). Natural forests Contribution of the co-authors Helen M. Wallace: Primary supervisor dominated by spotted gum species (section Maculatae) oc- of the PhD project this work was included in. cur widely throughout eastern Australia from high rainfall David J. Lee: Supervisor of the PhD project this work was included in. areas on coastal ranges through to drier inland sites (CPBR G. R. Dickinson 2006). Spotted gums are commercially very important and Department of Agriculture Fisheries and Forestry—Queensland, are amongst the most commonly harvested native hardwood P.O. Box 1054, Mareeba, QLD 4880, Australia timbers in the Australian states of Queensland and New South Wales (Lewis et al 2010). Many eucalypt species G. R. Dickinson (*) : H. M. Wallace : D. J. Lee University of the Sunshine Coast, (Corymbia and Eucalyptus) are of global economic signifi- Maroochydore DC, QLD 4558, Australia cance with >19 Mha established as timber plantations e-mail: [email protected] (Iglesias-Trabado and Wilstermann 2008). Corymbia spe- cies and their F1 hybrids are of increasing importance to D. J. Lee Department of Agriculture Fisheries and Forestry—Queensland, eucalypt plantation forestry due to their wide adaptability to P.O. Box 395, Gympie, QLD 4570, Australia marginal tropical and subtropical environments and high 2 G.R. Dickinson et al. quality, durable timber (Lee 2007). Over 20,000 ha of Suitor et al. 2008; Dickinson et al. 2012). Reproductive Corymbia plantations has been established across Australia isolation can continue after seeds are produced, resulting since the late 1990s (Barbour et al. 2008), primarily using in mortality and abnormal growth at germination, during Corymbia citriodora subsp. variegata. Selected Corymbia seedling development and as trees (Lopez et al. 2000; hybrids offer advantages over their parental species, such as Barbour et al. 2006; Volker et al. 2008; Lee et al. 2009; superior growth, disease, insect and frost tolerance, CostaeSilvaetal.2012). The activity of endogenous exhibited across a wide range of environments (Lee 2007; isolating barriers decreases with increasing taxonomic affin- Lee et al. 2009; Verma and Sharma 2011). In Australia, F1 ity between parents (Griffin et al. 1988; Ellis et al. 1991). Corymbia hybrids are derived by controlled pollination Infrageneric Corymbia clades are closely related (Hill and using Corymbia torelliana (section Torellianae)asthe Johnson 1995; Parra-O et al. 2009) and have an unusually maternal taxon and species from the spotted gum group high propensity to form interspecific hybrids across taxo- (section Maculatae); C. citriodora subsp. citriodora, C. nomic groups (Griffin et al. 1988; Dickinson et al. 2012). citriodora subsp. variegata or Corymbia henryi,asthe Hybridisation may also be greater when F1 hybrids are paternal taxon (Lee 2007; Dickinson et al. 2010). Many of backcrossed with either parental species (Potts et al. 2000, the areas in eastern Australia suitable for future Corymbia 2003). A better understanding of the breeding system and species and hybrid plantations are in close proximity to reproductive biology of Corymbia species and their F1 natural spotted gum populations. This raises concerns of hybrids is required to minimise future gene flow risks pollen-mediated gene flow from Corymbia plantations into (Barbour et al. 2008). sympatric native populations. Australian Corymbia hybrid programs have focused on Hybridisation results in gene flow between individuals, the production of F1 hybrids using C. torelliana as the contributing to plant speciation and evolution (Potts et al. maternal parent and a limited number of spotted gum taxa 2003; Arnold and Martin 2010; Costa e Silva et al. 2012). and families as the paternal parents (Lee 2007, Lee et al. Hybridisation can also cause genetic pollution via the 2009). Interspecific F1 hybridisation between C. torelliana pollen-mediated movement and introgression of foreign and other taxa is controlled by prezygotic isolating barriers, genes from exotic populations into sympatric native popu- with reproductive success increasing with increasing taxo- lations (Schierenbeck and Ellstrand 2009; Barbour et al. nomic affinity of parental taxa (Dickinson et al. 2012). 2010). Genetic pollution is an increasing global concern, There has, however, been little investigation of the repro- threatening the genetic purity of some native Populus spe- ductive success of advanced generation C. torelliana cies in Europe (Vanden Broeck et al. 2005; Ziegenhagen et hybrids. Knowledge of the hybridising potential of C. cit- al. 2008) and Eucalyptus (Potts et al. 2003; Barbour et al. riodora as the maternal parent is also poorly known, despite 2006, 2007, 2010)andCorymbia (Barbour et al. 2008) its international importance as a forestry plantation species species in Australia. Gene introgression occurs first by and wide natural distribution across eastern Australia. This hybridisation and then by repeated backcrossing to one or study aims to quantify the reproductive success of reciprocal both parents. This results in the alteration of natural patterns C. citriodora subsp. citriodora and C. torelliana hybrids, of genetic diversity and can potentially threaten the extinc- and advanced generation hybrids where both parental tion of pure species (Vanden Broeck et al. 2005; Barbour et species were backcrossed with C. torelliana × C. citriodora al. 2010). Gene introgression is controlled by ecological and subsp. citriodora or C. torelliana × C. citriodora subsp. genetic factors with hybrid populations often restricted to variegata F1 hybrid taxa. The activity and locations of narrow hybrid zones at native population boundaries reproductive isolation for these novel crosses will be deter- (Vanden Broeck et al. 2005; Barbour et al. 2006, 2010). mined via the assessment of pollen–pistil interactions, embryo Small, fragmented native populations with low genetic di- development and seed germination. Improved knowledge of versity, often of rare and